Pacemaker 1.1

Clusters from Scratch

Step-by-Step Instructions for Building Your First High-Availability Cluster

Edition 9

Andrew Beekhof

Primary author

Red Hat

andrew@beekhof.net

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Abstract

This document provides a step-by-step guide to building a simple high-availability cluster using Pacemaker.

The example cluster will use:

CentOS 7.5 as the host operating system
Corosync to provide messaging and membership services,
Pacemaker 1.1.18
DRBD as a cost-effective alternative to shared storage,
GFS2 as the cluster filesystem (in active/active mode)

Given the graphical nature of the install process, a number of screenshots are included. However the guide is primarily composed of commands, the reasons for executing them and their expected outputs.

Table of Contents

Preface

1. Document Conventions

1.1. Typographic Conventions
1.2. Pull-quote Conventions
1.3. Notes and Warnings

2. We Need Feedback!

1. Read-Me-First

1.1. The Scope of this Document

1.2. What Is Pacemaker?

1.3. Pacemaker Architecture

1.3.1. Internal Components

1.4. Types of Pacemaker Clusters

2. Installation

2.1. Install CentOS 7.5

2.1.1. Boot the Install Image
2.1.2. Installation Options
2.1.3. Configure Network
2.1.4. Configure Disk
2.1.5. Configure Time Synchronization
2.1.6. Finish Install

2.2. Configure the OS

2.2.1. Verify Networking
2.2.2. Login Remotely
2.2.3. Apply Updates
2.2.4. Use Short Node Names

2.3. Repeat for Second Node

2.4. Configure Communication Between Nodes

2.4.1. Configure Host Name Resolution
2.4.2. Configure SSH

2.5. Install the Cluster Software

2.6. Configure the Cluster Software

2.6.1. Allow cluster services through firewall
2.6.2. Enable pcs Daemon
2.6.3. Configure Corosync

3. Pacemaker Tools

3.1. Simplify administration using a cluster shell
3.2. Explore pcs

4. Start and Verify Cluster

4.1. Start the Cluster
4.2. Verify Corosync Installation
4.3. Verify Pacemaker Installation

5. Create an Active/Passive Cluster

5.1. Explore the Existing Configuration
5.2. Add a Resource
5.3. Perform a Failover
5.4. Prevent Resources from Moving after Recovery

6. Add Apache HTTP Server as a Cluster Service

6.1. Install Apache
6.2. Create Website Documents
6.3. Enable the Apache status URL
6.4. Configure the Cluster
6.5. Ensure Resources Run on the Same Host
6.6. Ensure Resources Start and Stop in Order
6.7. Prefer One Node Over Another
6.8. Move Resources Manually

7. Replicate Storage Using DRBD

7.1. Install the DRBD Packages
7.2. Allocate a Disk Volume for DRBD
7.3. Configure DRBD
7.4. Initialize DRBD
7.5. Populate the DRBD Disk
7.6. Configure the Cluster for the DRBD device
7.7. Configure the Cluster for the Filesystem
7.8. Test Cluster Failover

8. Configure STONITH

8.1. What is STONITH?
8.2. Choose a STONITH Device
8.3. Configure the Cluster for STONITH
8.4. Example

9. Convert Cluster to Active/Active

9.1. Install Cluster Filesystem Software
9.2. Configure the Cluster for the DLM
9.3. Create and Populate GFS2 Filesystem
9.4. Reconfigure the Cluster for GFS2
9.5. Clone the IP address
9.6. Clone the Filesystem and Apache Resources
9.7. Test Failover

A. Configuration Recap

A.1. Final Cluster Configuration

A.2. Node List

A.3. Cluster Options

A.4. Resources

A.4.1. Default Options
A.4.2. Fencing
A.4.3. Service Address
A.4.4. DRBD - Shared Storage
A.4.5. Cluster Filesystem
A.4.6. Apache

B. Sample Corosync Configuration

C. Further Reading

D. Revision History

Index

List of Figures

1.1. The Pacemaker Stack
1.2. Internal Components
1.3. Active/Passive Redundancy
1.4. Shared Failover
1.5. N to N Redundancy
2.1. CentOS 7.5 Installation Welcome Screen
2.2. CentOS 7.5 Installation Summary Screen
2.3. CentOS 7.5 Network Interface Screen
2.4. CentOS 7.5 Manual Partitioning Screen
2.5. CentOS 7.5 Console Prompt

List of Examples

5.1. The last XML you’ll see in this document

Preface

Table of Contents

1. Document Conventions

1.1. Typographic Conventions
1.2. Pull-quote Conventions
1.3. Notes and Warnings

2. We Need Feedback!

1. Document Conventions

This manual uses several conventions to highlight certain words and phrases and draw attention to specific pieces of information.

In PDF and paper editions, this manual uses typefaces drawn from the Liberation Fonts set. The Liberation Fonts set is also used in HTML editions if the set is installed on your system. If not, alternative but equivalent typefaces are displayed. Note: Red Hat Enterprise Linux 5 and later include the Liberation Fonts set by default.

1.1. Typographic Conventions

Four typographic conventions are used to call attention to specific words and phrases. These conventions, and the circumstances they apply to, are as follows.

Mono-spaced Bold

Used to highlight system input, including shell commands, file names and paths. Also used to highlight keys and key combinations. For example:

To see the contents of the file my_next_bestselling_novel in your current working directory, enter the cat my_next_bestselling_novel command at the shell prompt and press Enter to execute the command.

The above includes a file name, a shell command and a key, all presented in mono-spaced bold and all distinguishable thanks to context.

Key combinations can be distinguished from an individual key by the plus sign that connects each part of a key combination. For example:

Press Enter to execute the command.
Press Ctrl+Alt+F2 to switch to a virtual terminal.

The first example highlights a particular key to press. The second example highlights a key combination: a set of three keys pressed simultaneously.

If source code is discussed, class names, methods, functions, variable names and returned values mentioned within a paragraph will be presented as above, in mono-spaced bold. For example:

File-related classes include filesystem for file systems, file for files, and dir for directories. Each class has its own associated set of permissions.

Proportional Bold

This denotes words or phrases encountered on a system, including application names; dialog box text; labeled buttons; check-box and radio button labels; menu titles and sub-menu titles. For example:

Choose System → Preferences → Mouse from the main menu bar to launch Mouse Preferences. In the Buttons tab, select the Left-handed mouse check box and click Close to switch the primary mouse button from the left to the right (making the mouse suitable for use in the left hand).
To insert a special character into a gedit file, choose Applications → Accessories → Character Map from the main menu bar. Next, choose Search → Find… from the Character Map menu bar, type the name of the character in the Search field and click Next. The character you sought will be highlighted in the Character Table. Double-click this highlighted character to place it in the Text to copy field and then click the Copy button. Now switch back to your document and choose Edit → Paste from the gedit menu bar.

The above text includes application names; system-wide menu names and items; application-specific menu names; and buttons and text found within a GUI interface, all presented in proportional bold and all distinguishable by context.

Mono-spaced Bold Italic or Proportional Bold Italic

Whether mono-spaced bold or proportional bold, the addition of italics indicates replaceable or variable text. Italics denotes text you do not input literally or displayed text that changes depending on circumstance. For example:

To connect to a remote machine using ssh, type ssh username@domain.name at a shell prompt. If the remote machine is example.com and your username on that machine is john, type ssh john@example.com.
The mount -o remount file-system command remounts the named file system. For example, to remount the /home file system, the command is mount -o remount /home.
To see the version of a currently installed package, use the rpm -q package command. It will return a result as follows: package-version-release.

Note the words in bold italics above — username, domain.name, file-system, package, version and release. Each word is a placeholder, either for text you enter when issuing a command or for text displayed by the system.

Aside from standard usage for presenting the title of a work, italics denotes the first use of a new and important term. For example:

Publican is a DocBook publishing system.

1.2. Pull-quote Conventions

Terminal output and source code listings are set off visually from the surrounding text.

Output sent to a terminal is set in mono-spaced roman and presented thus:

books        Desktop   documentation  drafts  mss    photos   stuff  svn
books_tests  Desktop1  downloads      images  notes  scripts  svgs

Source-code listings are also set in mono-spaced roman but add syntax highlighting as follows:

package org.jboss.book.jca.ex1;

import javax.naming.InitialContext;

public class ExClient
{
   public static void main(String args[]) 
       throws Exception
   {
      InitialContext iniCtx = new InitialContext();
      Object         ref    = iniCtx.lookup("EchoBean");
      EchoHome       home   = (EchoHome) ref;
      Echo           echo   = home.create();

      System.out.println("Created Echo");

      System.out.println("Echo.echo('Hello') = " + echo.echo("Hello"));
   }
}

1.3. Notes and Warnings

Finally, we use three visual styles to draw attention to information that might otherwise be overlooked.

Note

Notes are tips, shortcuts or alternative approaches to the task at hand. Ignoring a note should have no negative consequences, but you might miss out on a trick that makes your life easier.

Important

Important boxes detail things that are easily missed: configuration changes that only apply to the current session, or services that need restarting before an update will apply. Ignoring a box labeled 'Important' will not cause data loss but may cause irritation and frustration.

Warning

Warnings should not be ignored. Ignoring warnings will most likely cause data loss.

2. We Need Feedback!

If you find a typographical error in this manual, or if you have thought of a way to make this manual better, we would love to hear from you! Please submit a report in Bugzilla ^[2] against the product Pacemaker.

When submitting a bug report, be sure to mention the manual's identifier: Clusters_from_Scratch

If you have a suggestion for improving the documentation, try to be as specific as possible when describing it. If you have found an error, please include the section number and some of the surrounding text so we can find it easily.

^[2] http://bugs.clusterlabs.org

Chapter 1. Read-Me-First

Table of Contents

1.1. The Scope of this Document

1.2. What Is Pacemaker?

1.3. Pacemaker Architecture

1.3.1. Internal Components

1.4. Types of Pacemaker Clusters

1.1. The Scope of this Document

Computer clusters can be used to provide highly available services or resources. The redundancy of multiple machines is used to guard against failures of many types.

This document will walk through the installation and setup of simple clusters using the CentOS distribution, version 7.5.

The clusters described here will use Pacemaker and Corosync to provide resource management and messaging. Required packages and modifications to their configuration files are described along with the use of the Pacemaker command line tool for generating the XML used for cluster control.

Pacemaker is a central component and provides the resource management required in these systems. This management includes detecting and recovering from the failure of various nodes, resources and services under its control.

When more in-depth information is required, and for real-world usage, please refer to the Pacemaker Explained manual.

1.2. What Is Pacemaker?

Pacemaker is a cluster resource manager, that is, a logic responsible for a life-cycle of deployed software — indirectly perhaps even whole systems or their interconnections — under its control within a set of computers (a.k.a. nodes) and driven by prescribed rules.

It achieves maximum availability for your cluster services (a.k.a. resources) by detecting and recovering from node- and resource-level failures by making use of the messaging and membership capabilities provided by your preferred cluster infrastructure (either Corosync or Heartbeat), and possibly by utilizing other parts of the overall cluster stack.

Note

For the goal of minimal downtime a term high availability was coined and together with its acronym, HA, is well-established in the sector. To differentiate this sort of clusters from high performance computing (HPC) ones, should a context require it (apparently, not the case in this document), using HA cluster is an option.

Pacemaker’s key features include:

Detection and recovery of node and service-level failures
Storage agnostic, no requirement for shared storage
Resource agnostic, anything that can be scripted can be clustered
Supports fencing (also referred to as the STONITH acronym, deciphered later on) for ensuring data integrity
Supports large and small clusters
Supports both quorate and resource-driven clusters
Supports practically any redundancy configuration
Automatically replicated configuration that can be updated from any node
Ability to specify cluster-wide service ordering, colocation and anti-colocation
Support for advanced service types
- Clones: for services which need to be active on multiple nodes
- Multi-state: for services with multiple modes (e.g. master/slave, primary/secondary)
Unified, scriptable cluster management tools

1.3. Pacemaker Architecture

At the highest level, the cluster is made up of three pieces:

Non-cluster-aware components. These pieces include the resources themselves; scripts that start, stop and monitor them; and a local daemon that masks the differences between the different standards these scripts implement. Even though interactions of these resources when run as multiple instances can resemble a distributed system, they still lack the proper HA mechanisms and/or autonomous cluster-wide governance as subsumed in the following item.
Resource management. Pacemaker provides the brain that processes and reacts to events regarding the cluster. These events include nodes joining or leaving the cluster; resource events caused by failures, maintenance and scheduled activities; and other administrative actions. Pacemaker will compute the ideal state of the cluster and plot a path to achieve it after any of these events. This may include moving resources, stopping nodes and even forcing them offline with remote power switches.
Low-level infrastructure. Projects like Corosync, CMAN and Heartbeat provide reliable messaging, membership and quorum information about the cluster.

When combined with Corosync, Pacemaker also supports popular open source cluster filesystems.^[3]

Due to past standardization within the cluster filesystem community, cluster filesystems make use of a common distributed lock manager, which makes use of Corosync for its messaging and membership capabilities (which nodes are up/down) and Pacemaker for fencing services.

Figure 1.1. The Pacemaker Stack

1.3.1. Internal Components

Pacemaker itself is composed of five key components:

Cluster Information Base (CIB)
Cluster Resource Management daemon (CRMd)
Local Resource Management daemon (LRMd)
Policy Engine (PEngine or PE)
Fencing daemon (STONITHd)

Figure 1.2. Internal Components

The CIB uses XML to represent both the cluster’s configuration and current state of all resources in the cluster. The contents of the CIB are automatically kept in sync across the entire cluster and are used by the PEngine to compute the ideal state of the cluster and how it should be achieved.

This list of instructions is then fed to the Designated Controller (DC). Pacemaker centralizes all cluster decision making by electing one of the CRMd instances to act as a master. Should the elected CRMd process (or the node it is on) fail, a new one is quickly established.

The DC carries out the PEngine’s instructions in the required order by passing them to either the Local Resource Management daemon (LRMd) or CRMd peers on other nodes via the cluster messaging infrastructure (which in turn passes them on to their LRMd process).

The peer nodes all report the results of their operations back to the DC and, based on the expected and actual results, will either execute any actions that needed to wait for the previous one to complete, or abort processing and ask the PEngine to recalculate the ideal cluster state based on the unexpected results.

In some cases, it may be necessary to power off nodes in order to protect shared data or complete resource recovery. For this, Pacemaker comes with STONITHd.

Note

STONITH is an acronym for Shoot-The-Other-Node-In-The-Head, a recommended practice that misbehaving node is best to be promptly fenced (shut off, cut from shared resources or otherwise immobilized), and is usually implemented with a remote power switch.

In Pacemaker, STONITH devices are modeled as resources (and configured in the CIB) to enable them to be easily monitored for failure, however STONITHd takes care of understanding the STONITH topology such that its clients simply request a node be fenced, and it does the rest.

1.4. Types of Pacemaker Clusters

Pacemaker makes no assumptions about your environment. This allows it to support practically any redundancy configuration including Active/Active, Active/Passive, N+1, N+M, N-to-1 and N-to-N.

Figure 1.3. Active/Passive Redundancy

Two-node Active/Passive clusters using Pacemaker and DRBD are a cost-effective solution for many High Availability situations.

Figure 1.4. Shared Failover

By supporting many nodes, Pacemaker can dramatically reduce hardware costs by allowing several active/passive clusters to be combined and share a common backup node.

Figure 1.5. N to N Redundancy

When shared storage is available, every node can potentially be used for failover. Pacemaker can even run multiple copies of services to spread out the workload.

^[3] Even though Pacemaker also supports Heartbeat, the filesystems need to use the stack for messaging and membership, and Corosync seems to be what they’re standardizing on. Technically, it would be possible for them to support Heartbeat as well, but there seems little interest in this.

Chapter 2. Installation

2.1. Install CentOS 7.5

2.1.1. Boot the Install Image

Download the 4GB CentOS 7.5 DVD ISO. Use the image to boot a virtual machine, or burn it to a DVD or USB drive and boot a physical server from that.

After starting the installation, select your language and keyboard layout at the welcome screen.

Figure 2.1. CentOS 7.5 Installation Welcome Screen

2.1.2. Installation Options

At this point, you get a chance to tweak the default installation options.

Figure 2.2. CentOS 7.5 Installation Summary Screen

Ignore the SOFTWARE SELECTION section (try saying that 10 times quickly). The Infrastructure Server environment does have add-ons with much of the software we need, but we will leave it as a Minimal Install here, so that we can see exactly what software is required later.

2.1.3. Configure Network

In the NETWORK & HOSTNAME section:

Edit Host Name: as desired. For this example, we will use pcmk-1.localdomain.
Select your network device, press Configure…, and manually assign a fixed IP address. For this example, we’ll use 192.168.122.101 under IPv4 Settings (with an appropriate netmask, gateway and DNS server).
Flip the switch to turn your network device on, and press Done.

Figure 2.3. CentOS 7.5 Network Interface Screen

Important

Do not accept the default network settings. Cluster machines should never obtain an IP address via DHCP, because DHCP’s periodic address renewal will interfere with corosync.

2.1.4. Configure Disk

By default, the installer’s automatic partitioning will use LVM (which allows us to dynamically change the amount of space allocated to a given partition). However, it allocates all free space to the / (aka. root) partition, which cannot be reduced in size later (dynamic increases are fine).

In order to follow the DRBD and GFS2 portions of this guide, we need to reserve space on each machine for a replicated volume.

Enter the INSTALLATION DESTINATION section, ensure the hard drive you want to install to is selected, select I will configure partitioning, and press Done.

In the MANUAL PARTITIONING screen that comes next, click the option to create mountpoints automatically. Select the / mountpoint, and reduce the desired capacity by 1GiB or so. Select Modify… by the volume group name, and change the Size policy: to As large as possible, to make the reclaimed space available inside the LVM volume group. We’ll add the additional volume later.

Figure 2.4. CentOS 7.5 Manual Partitioning Screen

Press Done, then Accept changes.

2.1.5. Configure Time Synchronization

It is highly recommended to enable NTP on your cluster nodes. Doing so ensures all nodes agree on the current time and makes reading log files significantly easier.

CentOS will enable NTP automatically. If you want to change any time-related settings (such as time zone or NTP server), you can do this in the TIME & DATE section.

2.1.6. Finish Install

Select Begin Installation. Once it completes, set a root password, and reboot as instructed. For the purposes of this document, it is not necessary to create any additional users. After the node reboots, you’ll see a login prompt on the console. Login using root and the password you created earlier.

Figure 2.5. CentOS 7.5 Console Prompt

Note

From here on, we’re going to be working exclusively from the terminal.

2.2. Configure the OS

2.2.1. Verify Networking

Ensure that the machine has the static IP address you configured earlier.

[root@pcmk-1 ~]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 52:54:00:8e:eb:41 brd ff:ff:ff:ff:ff:ff
    inet 192.168.122.101/24 brd 192.168.122.255 scope global noprefixroute eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::e45:c99b:34c0:c657/64 scope link noprefixroute
       valid_lft forever preferred_lft forever

Note

If you ever need to change the node’s IP address from the command line, follow

[root@pcmk-1 ~]# vi /etc/sysconfig/network-scripts/ifcfg-${device} # manually edit as desired
[root@pcmk-1 ~]# nmcli dev disconnect ${device}
[root@pcmk-1 ~]# nmcli con reload ${device}
[root@pcmk-1 ~]# nmcli con up ${device}

This makes NetworkManager aware that a change was made on the config file.

Next, ensure that the routes are as expected:

[root@pcmk-1 ~]# ip route
default via 192.168.122.1 dev eth0 proto static metric 100
192.168.122.0/24 dev eth0 proto kernel scope link src 192.168.122.101 metric 100

If there is no line beginning with default via, then you may need to add a line such as

GATEWAY="192.168.122.1"

to the device configuration using the same process as described above for changing the IP address.

Now, check for connectivity to the outside world. Start small by testing whether we can reach the gateway we configured.

[root@pcmk-1 ~]# ping -c 1 192.168.122.1
PING 192.168.122.1 (192.168.122.1) 56(84) bytes of data.
64 bytes from 192.168.122.1: icmp_seq=1 ttl=64 time=0.254 ms

--- 192.168.122.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.254/0.254/0.254/0.000 ms

Now try something external; choose a location you know should be available.

[root@pcmk-1 ~]# ping -c 1 www.clusterlabs.org
PING oss-uk-1.clusterlabs.org (109.74.197.241) 56(84) bytes of data.
64 bytes from oss-uk-1.clusterlabs.org (109.74.197.241): icmp_seq=1 ttl=49 time=333 ms

--- oss-uk-1.clusterlabs.org ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 333.204/333.204/333.204/0.000 ms

2.2.2. Login Remotely

The console isn’t a very friendly place to work from, so we will now switch to accessing the machine remotely via SSH where we can use copy and paste, etc.

From another host, check whether we can see the new host at all:

beekhof@f16 ~ # ping -c 1 192.168.122.101
PING 192.168.122.101 (192.168.122.101) 56(84) bytes of data.
64 bytes from 192.168.122.101: icmp_req=1 ttl=64 time=1.01 ms

--- 192.168.122.101 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 1.012/1.012/1.012/0.000 ms

Next, login as root via SSH.

beekhof@f16 ~ # ssh -l root 192.168.122.101
The authenticity of host '192.168.122.101 (192.168.122.101)' can't be established.
ECDSA key fingerprint is 6e:b7:8f:e2:4c:94:43:54:a8:53:cc:20:0f:29:a4:e0.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.122.101' (ECDSA) to the list of known hosts.
root@192.168.122.101's password:
Last login: Tue Aug 11 13:14:39 2015
[root@pcmk-1 ~]#

2.2.3. Apply Updates

Apply any package updates released since your installation image was created:

[root@pcmk-1 ~]# yum update

2.2.4. Use Short Node Names

During installation, we filled in the machine’s fully qualified domain name (FQDN), which can be rather long when it appears in cluster logs and status output. See for yourself how the machine identifies itself:

[root@pcmk-1 ~]# uname -n
pcmk-1.localdomain

We can use the hostnamectl tool to strip off the domain name:

[root@pcmk-1 ~]# hostnamectl set-hostname $(uname -n | sed s/\\..*//)

Now, check that the machine is using the correct name:

[root@pcmk-1 ~]# uname -n
pcmk-1

You may want to reboot to ensure all updates take effect.

2.3. Repeat for Second Node

Repeat the Installation steps so far, so that you have two nodes ready to have the cluster software installed.

For the purposes of this document, the additional node is called pcmk-2 with address 192.168.122.102.

2.4. Configure Communication Between Nodes

2.4.1. Configure Host Name Resolution

Confirm that you can communicate between the two new nodes:

[root@pcmk-1 ~]# ping -c 3 192.168.122.102
PING 192.168.122.102 (192.168.122.102) 56(84) bytes of data.
64 bytes from 192.168.122.102: icmp_seq=1 ttl=64 time=0.343 ms
64 bytes from 192.168.122.102: icmp_seq=2 ttl=64 time=0.402 ms
64 bytes from 192.168.122.102: icmp_seq=3 ttl=64 time=0.558 ms

--- 192.168.122.102 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2000ms
rtt min/avg/max/mdev = 0.343/0.434/0.558/0.092 ms

Now we need to make sure we can communicate with the machines by their name. If you have a DNS server, add additional entries for the two machines. Otherwise, you’ll need to add the machines to /etc/hosts on both nodes. Below are the entries for my cluster nodes:

[root@pcmk-1 ~]# grep pcmk /etc/hosts
192.168.122.101 pcmk-1.clusterlabs.org pcmk-1
192.168.122.102 pcmk-2.clusterlabs.org pcmk-2

We can now verify the setup by again using ping:

[root@pcmk-1 ~]# ping -c 3 pcmk-2
PING pcmk-2.clusterlabs.org (192.168.122.101) 56(84) bytes of data.
64 bytes from pcmk-1.clusterlabs.org (192.168.122.101): icmp_seq=1 ttl=64 time=0.164 ms
64 bytes from pcmk-1.clusterlabs.org (192.168.122.101): icmp_seq=2 ttl=64 time=0.475 ms
64 bytes from pcmk-1.clusterlabs.org (192.168.122.101): icmp_seq=3 ttl=64 time=0.186 ms

--- pcmk-2.clusterlabs.org ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2001ms
rtt min/avg/max/mdev = 0.164/0.275/0.475/0.141 ms

2.4.2. Configure SSH

SSH is a convenient and secure way to copy files and perform commands remotely. For the purposes of this guide, we will create a key without a password (using the -N option) so that we can perform remote actions without being prompted.

Warning

Unprotected SSH keys (those without a password) are not recommended for servers exposed to the outside world. We use them here only to simplify the demo.

Create a new key and allow anyone with that key to log in:

Creating and Activating a new SSH Key

[root@pcmk-1 ~]# ssh-keygen -t dsa -f ~/.ssh/id_dsa -N ""
Generating public/private dsa key pair.
Your identification has been saved in /root/.ssh/id_dsa.
Your public key has been saved in /root/.ssh/id_dsa.pub.
The key fingerprint is:
91:09:5c:82:5a:6a:50:08:4e:b2:0c:62:de:cc:74:44 root@pcmk-1.clusterlabs.org
The key's randomart image is:
+--[ DSA 1024]----+
|==.ooEo..        |
|X O + .o o       |
| * A    +        |
|  +      .       |
| .      S        |
|                 |
|                 |
|                 |
|                 |
+-----------------+
[root@pcmk-1 ~]# cp ~/.ssh/id_dsa.pub ~/.ssh/authorized_keys

Install the key on the other node:

[root@pcmk-1 ~]# scp -r ~/.ssh pcmk-2:
The authenticity of host 'pcmk-2 (192.168.122.102)' can't be established.
ECDSA key fingerprint is SHA256:63xNPkPYq98rYznf3T9QYJAzlaGiAsSgFVNHOZjPWqc.
ECDSA key fingerprint is MD5:d9:bf:6e:32:88:be:47:3d:96:f1:96:27:65:05:0b:c3.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'pcmk-2,192.168.122.102' (ECDSA) to the list of known hosts.
root@pcmk-2's password:
id_dsa
id_dsa.pub
authorized_keys
known_hosts

Test that you can now run commands remotely, without being prompted:

[root@pcmk-1 ~]# ssh pcmk-2 -- uname -n
pcmk-2

2.5. Install the Cluster Software

Fire up a shell on both nodes and run the following to install pacemaker, and while we’re at it, some command-line tools to make our lives easier:

# yum install -y pacemaker pcs psmisc policycoreutils-python

Important

This document will show commands that need to be executed on both nodes with a simple # prompt. Be sure to run them on each node individually.

Note

This document uses pcs for cluster management. Other alternatives, such as crmsh, are available, but their syntax will differ from the examples used here.

2.6. Configure the Cluster Software

2.6.1. Allow cluster services through firewall

On each node, allow cluster-related services through the local firewall:

# firewall-cmd --permanent --add-service=high-availability
success
# firewall-cmd --reload
success

Note

If you are using iptables directly, or some other firewall solution besides firewalld, simply open the following ports, which can be used by various clustering components: TCP ports 2224, 3121, and 21064, and UDP port 5405.

If you run into any problems during testing, you might want to disable the firewall and SELinux entirely until you have everything working. This may create significant security issues and should not be performed on machines that will be exposed to the outside world, but may be appropriate during development and testing on a protected host.

To disable security measures:

[root@pcmk-1 ~]# setenforce 0
[root@pcmk-1 ~]# sed -i.bak "s/SELINUX=enforcing/SELINUX=permissive/g" /etc/selinux/config
[root@pcmk-1 ~]# systemctl mask firewalld.service
[root@pcmk-1 ~]# systemctl stop firewalld.service
[root@pcmk-1 ~]# iptables --flush

2.6.2. Enable pcs Daemon

Before the cluster can be configured, the pcs daemon must be started and enabled to start at boot time on each node. This daemon works with the pcs command-line interface to manage synchronizing the corosync configuration across all nodes in the cluster.

Start and enable the daemon by issuing the following commands on each node:

# systemctl start pcsd.service
# systemctl enable pcsd.service
Created symlink from /etc/systemd/system/multi-user.target.wants/pcsd.service to /usr/lib/systemd/system/pcsd.service.

The installed packages will create a hacluster user with a disabled password. While this is fine for running pcs commands locally, the account needs a login password in order to perform such tasks as syncing the corosync configuration, or starting and stopping the cluster on other nodes.

This tutorial will make use of such commands, so now we will set a password for the hacluster user, using the same password on both nodes:

# passwd hacluster
Changing password for user hacluster.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.

Note

Alternatively, to script this process or set the password on a different machine from the one you’re logged into, you can use the --stdin option for passwd:

[root@pcmk-1 ~]# ssh pcmk-2 -- 'echo mysupersecretpassword | passwd --stdin hacluster'

2.6.3. Configure Corosync

On either node, use pcs cluster auth to authenticate as the hacluster user:

[root@pcmk-1 ~]# pcs cluster auth pcmk-1 pcmk-2
Username: hacluster
Password:
pcmk-2: Authorized
pcmk-1: Authorized

Next, use pcs cluster setup on the same node to generate and synchronize the corosync configuration:

[root@pcmk-1 ~]# pcs cluster setup --name mycluster pcmk-1 pcmk-2
Destroying cluster on nodes: pcmk-1, pcmk-2...
pcmk-2: Stopping Cluster (pacemaker)...
pcmk-1: Stopping Cluster (pacemaker)...
pcmk-1: Successfully destroyed cluster
pcmk-2: Successfully destroyed cluster

Sending 'pacemaker_remote authkey' to 'pcmk-1', 'pcmk-2'
pcmk-2: successful distribution of the file 'pacemaker_remote authkey'
pcmk-1: successful distribution of the file 'pacemaker_remote authkey'
Sending cluster config files to the nodes...
pcmk-1: Succeeded
pcmk-2: Succeeded

Synchronizing pcsd certificates on nodes pcmk-1, pcmk-2...
pcmk-2: Success
pcmk-1: Success
Restarting pcsd on the nodes in order to reload the certificates...
pcmk-2: Success
pcmk-1: Success

If you received an authorization error for either of those commands, make sure you configured the hacluster user account on each node with the same password.

Note

If you are not using pcs for cluster administration, follow whatever procedures are appropriate for your tools to create a corosync.conf and copy it to all nodes.

The pcs command will configure corosync to use UDP unicast transport; if you choose to use multicast instead, choose a multicast address carefully. ^[4]

The final corosync.conf configuration on each node should look something like the sample in Appendix B, Sample Corosync Configuration.

^[4] For some subtle issues, see Topics in High-Performance Messaging: Multicast Address Assignment or the more detailed treatment in Cisco’s Guidelines for Enterprise IP Multicast Address Allocation.

Chapter 3. Pacemaker Tools

Table of Contents

3.1. Simplify administration using a cluster shell
3.2. Explore pcs

3.1. Simplify administration using a cluster shell

In the dark past, configuring Pacemaker required the administrator to read and write XML. In true UNIX style, there were also a number of different commands that specialized in different aspects of querying and updating the cluster.

All of that has been greatly simplified with the creation of unified command-line shells (and GUIs) that hide all the messy XML scaffolding.

These shells take all the individual aspects required for managing and configuring a cluster, and pack them into one simple-to-use command line tool.

They even allow you to queue up several changes at once and commit them all at once.

Two popular command-line shells are pcs and crmsh. Clusters from Scratch is based on pcs because it comes with CentOS, but both have similar functionality. Choosing a shell or GUI is a matter of personal preference and what comes with (and perhaps is supported by) your choice of operating system.

3.2. Explore pcs

Start by taking some time to familiarize yourself with what pcs can do.

[root@pcmk-1 ~]# pcs

Usage: pcs [-f file] [-h] [commands]...
Control and configure pacemaker and corosync.

Options:
    -h, --help         Display usage and exit.
    -f file            Perform actions on file instead of active CIB.
    --debug            Print all network traffic and external commands run.
    --version          Print pcs version information. List pcs capabilities if
                       --full is specified.
    --request-timeout  Timeout for each outgoing request to another node in
                       seconds. Default is 60s.
    --force            Override checks and errors, the exact behavior depends on
                       the command. WARNING: Using the --force option is
                       strongly discouraged unless you know what you are doing.

Commands:
    cluster     Configure cluster options and nodes.
    resource    Manage cluster resources.
    stonith     Manage fence devices.
    constraint  Manage resource constraints.
    property    Manage pacemaker properties.
    acl         Manage pacemaker access control lists.
    qdevice     Manage quorum device provider on the local host.
    quorum      Manage cluster quorum settings.
    booth       Manage booth (cluster ticket manager).
    status      View cluster status.
    config      View and manage cluster configuration.
    pcsd        Manage pcs daemon.
    node        Manage cluster nodes.
    alert       Manage pacemaker alerts.

As you can see, the different aspects of cluster management are separated into categories. To discover the functionality available in each of these categories, one can issue the command pcs category help. Below is an example of all the options available under the status category.

[root@pcmk-1 ~]# pcs status help

Usage: pcs status [commands]...
View current cluster and resource status
Commands:
    [status] [--full | --hide-inactive]
        View all information about the cluster and resources (--full provides
        more details, --hide-inactive hides inactive resources).

    resources [<resource id> | --full | --groups | --hide-inactive]
        Show all currently configured resources or if a resource is specified
        show the options for the configured resource.  If --full is specified,
        all configured resource options will be displayed.  If --groups is
        specified, only show groups (and their resources).  If --hide-inactive
        is specified, only show active resources.

    groups
        View currently configured groups and their resources.

    cluster
        View current cluster status.

    corosync
        View current membership information as seen by corosync.

    quorum
        View current quorum status.

    qdevice <device model> [--full] [<cluster name>]
        Show runtime status of specified model of quorum device provider.  Using
        --full will give more detailed output.  If <cluster name> is specified,
        only information about the specified cluster will be displayed.

    nodes [corosync | both | config]
        View current status of nodes from pacemaker. If 'corosync' is
        specified, view current status of nodes from corosync instead. If
        'both' is specified, view current status of nodes from both corosync &
        pacemaker. If 'config' is specified, print nodes from corosync &
        pacemaker configuration.

    pcsd [<node>]...
        Show current status of pcsd on nodes specified, or on all nodes
        configured in the local cluster if no nodes are specified.

    xml
        View xml version of status (output from crm_mon -r -1 -X).

Additionally, if you are interested in the version and supported cluster stack(s) available with your Pacemaker installation, run:

[root@pcmk-1 ~]# pacemakerd --features
Pacemaker 1.1.18-11.el7_5.3 (Build: 2b07d5c5a9)
 Supporting v3.0.14:  generated-manpages agent-manpages ncurses libqb-logging libqb-ipc systemd nagios  corosync-native atomic-attrd acls

Note

If the SNMP and/or email options are not listed, then Pacemaker was not built to support them. This may be by the choice of your distribution, or the required libraries may not have been available. Please contact whoever supplied you with the packages for more details.

Chapter 4. Start and Verify Cluster

Table of Contents

4.1. Start the Cluster
4.2. Verify Corosync Installation
4.3. Verify Pacemaker Installation

4.1. Start the Cluster

Now that corosync is configured, it is time to start the cluster. The command below will start corosync and pacemaker on both nodes in the cluster. If you are issuing the start command from a different node than the one you ran the pcs cluster auth command on earlier, you must authenticate on the current node you are logged into before you will be allowed to start the cluster.

[root@pcmk-1 ~]# pcs cluster start --all
pcmk-1: Starting Cluster...
pcmk-2: Starting Cluster...

Note

An alternative to using the pcs cluster start --all command is to issue either of the below command sequences on each node in the cluster separately:

# pcs cluster start
Starting Cluster...

# systemctl start corosync.service
# systemctl start pacemaker.service

Important

In this example, we are not enabling the corosync and pacemaker services to start at boot. If a cluster node fails or is rebooted, you will need to run pcs cluster start nodename (or --all) to start the cluster on it. While you could enable the services to start at boot, requiring a manual start of cluster services gives you the opportunity to do a post-mortem investigation of a node failure before returning it to the cluster.

4.2. Verify Corosync Installation

First, use corosync-cfgtool to check whether cluster communication is happy:

[root@pcmk-1 ~]# corosync-cfgtool -s
Printing ring status.
Local node ID 1
RING ID 0
        id      = 192.168.122.101
        status  = ring 0 active with no faults

We can see here that everything appears normal with our fixed IP address (not a 127.0.0.x loopback address) listed as the id, and no faults for the status.

If you see something different, you might want to start by checking the node’s network, firewall and SELinux configurations.

Next, check the membership and quorum APIs:

[root@pcmk-1 ~]# corosync-cmapctl | grep members
runtime.totem.pg.mrp.srp.members.1.config_version (u64) = 0
runtime.totem.pg.mrp.srp.members.1.ip (str) = r(0) ip(192.168.122.101)
runtime.totem.pg.mrp.srp.members.1.join_count (u32) = 1
runtime.totem.pg.mrp.srp.members.1.status (str) = joined
runtime.totem.pg.mrp.srp.members.2.config_version (u64) = 0
runtime.totem.pg.mrp.srp.members.2.ip (str) = r(0) ip(192.168.122.102)
runtime.totem.pg.mrp.srp.members.2.join_count (u32) = 1
runtime.totem.pg.mrp.srp.members.2.status (str) = joined

[root@pcmk-1 ~]# pcs status corosync

Membership information
\----------------------
    Nodeid      Votes Name
         1          1 pcmk-1 (local)
         2          1 pcmk-2

You should see both nodes have joined the cluster.

4.3. Verify Pacemaker Installation

Now that we have confirmed that Corosync is functional, we can check the rest of the stack. Pacemaker has already been started, so verify the necessary processes are running:

[root@pcmk-1 ~]# ps axf
  PID TTY      STAT   TIME COMMAND
    2 ?        S      0:00 [kthreadd]
...lots of processes...
 1362 ?        Ssl    0:35 corosync
 1379 ?        Ss     0:00 /usr/sbin/pacemakerd -f
 1380 ?        Ss     0:00  \_ /usr/libexec/pacemaker/cib
 1381 ?        Ss     0:00  \_ /usr/libexec/pacemaker/stonithd
 1382 ?        Ss     0:00  \_ /usr/libexec/pacemaker/lrmd
 1383 ?        Ss     0:00  \_ /usr/libexec/pacemaker/attrd
 1384 ?        Ss     0:00  \_ /usr/libexec/pacemaker/pengine
 1385 ?        Ss     0:00  \_ /usr/libexec/pacemaker/crmd

If that looks OK, check the pcs status output:

[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
WARNING: no stonith devices and stonith-enabled is not false
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 16:37:34 2018
Last change: Mon Sep 10 16:30:53 2018 by hacluster via crmd on pcmk-2

2 nodes configured
0 resources configured

Online: [ pcmk-1 pcmk-2 ]

No resources


Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

Finally, ensure there are no start-up errors from corosync or pacemaker (aside from messages relating to not having STONITH configured, which are OK at this point):

[root@pcmk-1 ~]# journalctl -b | grep -i error

Note

Other operating systems may report startup errors in other locations, for example /var/log/messages.

Repeat these checks on the other node. The results should be the same.

Chapter 5. Create an Active/Passive Cluster

Table of Contents

5.1. Explore the Existing Configuration
5.2. Add a Resource
5.3. Perform a Failover
5.4. Prevent Resources from Moving after Recovery

5.1. Explore the Existing Configuration

When Pacemaker starts up, it automatically records the number and details of the nodes in the cluster, as well as which stack is being used and the version of Pacemaker being used.

The first few lines of output should look like this:

[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
WARNING: no stonith devices and stonith-enabled is not false
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 16:41:46 2018
Last change: Mon Sep 10 16:30:53 2018 by hacluster via crmd on pcmk-2

2 nodes configured
0 resources configured

Online: [ pcmk-1 pcmk-2 ]

For those who are not of afraid of XML, you can see the raw cluster configuration and status by using the pcs cluster cib command.

Example 5.1. The last XML you’ll see in this document

[root@pcmk-1 ~]# pcs cluster cib

<cib crm_feature_set="3.0.14" validate-with="pacemaker-2.10" epoch="5" num_updates="4" admin_epoch="0" cib-last-written="Mon Sep 10 16:30:53 2018" update-origin="pcmk-2" update-client="crmd" update-user="hacluster" have-quorum="1" dc-uuid="2">
  <configuration>
    <crm_config>
      <cluster_property_set id="cib-bootstrap-options">
        <nvpair id="cib-bootstrap-options-have-watchdog" name="have-watchdog" value="false"/>
        <nvpair id="cib-bootstrap-options-dc-version" name="dc-version" value="1.1.18-11.el7_5.3-2b07d5c5a9"/>
        <nvpair id="cib-bootstrap-options-cluster-infrastructure" name="cluster-infrastructure" value="corosync"/>
        <nvpair id="cib-bootstrap-options-cluster-name" name="cluster-name" value="mycluster"/>
      </cluster_property_set>
    </crm_config>
    <nodes>
      <node id="1" uname="pcmk-1"/>
      <node id="2" uname="pcmk-2"/>
    </nodes>
    <resources/>
    <constraints/>
  </configuration>
  <status>
    <node_state id="1" uname="pcmk-1" in_ccm="true" crmd="online" crm-debug-origin="do_state_transition" join="member" expected="member">
      <lrm id="1">
        <lrm_resources/>
      </lrm>
    </node_state>
    <node_state id="2" uname="pcmk-2" in_ccm="true" crmd="online" crm-debug-origin="do_state_transition" join="member" expected="member">
      <lrm id="2">
        <lrm_resources/>
      </lrm>
    </node_state>
  </status>
</cib>

Before we make any changes, it’s a good idea to check the validity of the configuration.

[root@pcmk-1 ~]# crm_verify -L -V
   error: unpack_resources: Resource start-up disabled since no STONITH resources have been defined
   error: unpack_resources: Either configure some or disable STONITH with the stonith-enabled option
   error: unpack_resources: NOTE: Clusters with shared data need STONITH to ensure data integrity
Errors found during check: config not valid

As you can see, the tool has found some errors.

In order to guarantee the safety of your data, ^[5] fencing (also called STONITH) is enabled by default. However, it also knows when no STONITH configuration has been supplied and reports this as a problem (since the cluster will not be able to make progress if a situation requiring node fencing arises).

We will disable this feature for now and configure it later.

To disable STONITH, set the stonith-enabled cluster option to false:

[root@pcmk-1 ~]# pcs property set stonith-enabled=false
[root@pcmk-1 ~]# crm_verify -L

With the new cluster option set, the configuration is now valid.

Warning

The use of stonith-enabled=false is completely inappropriate for a production cluster. It tells the cluster to simply pretend that failed nodes are safely powered off. Some vendors will refuse to support clusters that have STONITH disabled. We disable STONITH here only to defer the discussion of its configuration, which can differ widely from one installation to the next. See Section 8.1, “What is STONITH?” for information on why STONITH is important and details on how to configure it.

5.2. Add a Resource

Our first resource will be a unique IP address that the cluster can bring up on either node. Regardless of where any cluster service(s) are running, end users need a consistent address to contact them on. Here, I will choose 192.168.122.120 as the floating address, give it the imaginative name ClusterIP and tell the cluster to check whether it is running every 30 seconds.

Warning

The chosen address must not already be in use on the network. Do not reuse an IP address one of the nodes already has configured.

[root@pcmk-1 ~]# pcs resource create ClusterIP ocf:heartbeat:IPaddr2 \
    ip=192.168.122.120 cidr_netmask=32 op monitor interval=30s

Another important piece of information here is ocf:heartbeat:IPaddr2. This tells Pacemaker three things about the resource you want to add:

The first field (ocf in this case) is the standard to which the resource script conforms and where to find it.
The second field (heartbeat in this case) is standard-specific; for OCF resources, it tells the cluster which OCF namespace the resource script is in.
The third field (IPaddr2 in this case) is the name of the resource script.

To obtain a list of the available resource standards (the ocf part of ocf:heartbeat:IPaddr2), run:

[root@pcmk-1 ~]# pcs resource standards
lsb
ocf
service
systemd

To obtain a list of the available OCF resource providers (the heartbeat part of ocf:heartbeat:IPaddr2), run:

[root@pcmk-1 ~]# pcs resource providers
heartbeat
openstack
pacemaker

Finally, if you want to see all the resource agents available for a specific OCF provider (the IPaddr2 part of ocf:heartbeat:IPaddr2), run:

[root@pcmk-1 ~]# pcs resource agents ocf:heartbeat
apache
aws-vpc-move-ip
awseip
awsvip
azure-lb
clvm
.
. (skipping lots of resources to save space)
.
symlink
tomcat
VirtualDomain
Xinetd

Now, verify that the IP resource has been added, and display the cluster’s status to see that it is now active:

[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 16:55:26 2018
Last change: Mon Sep 10 16:53:42 2018 by root via cibadmin on pcmk-1

2 nodes configured
1 resource configured

Online: [ pcmk-1 pcmk-2 ]

Full list of resources:

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-1

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

5.3. Perform a Failover

Since our ultimate goal is high availability, we should test failover of our new resource before moving on.

First, find the node on which the IP address is running.

[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 16:55:26 2018
Last change: Mon Sep 10 16:53:42 2018 by root via cibadmin on pcmk-1

2 nodes configured
1 resource configured

Online: [ pcmk-1 pcmk-2 ]

Full list of resources:

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-1

You can see that the status of the ClusterIP resource is Started on a particular node (in this example, pcmk-1). Shut down Pacemaker and Corosync on that machine to trigger a failover.

[root@pcmk-1 ~]# pcs cluster stop pcmk-1
Stopping Cluster (pacemaker)...
Stopping Cluster (corosync)...

Note

A cluster command such as pcs cluster stop nodename can be run from any node in the cluster, not just the affected node.

Verify that pacemaker and corosync are no longer running:

[root@pcmk-1 ~]# pcs status
Error: cluster is not currently running on this node

Go to the other node, and check the cluster status.

[root@pcmk-2 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 16:57:22 2018
Last change: Mon Sep 10 16:53:42 2018 by root via cibadmin on pcmk-1

2 nodes configured
1 resource configured

Online: [ pcmk-2 ]
OFFLINE: [ pcmk-1 ]

Full list of resources:

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-2

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

Notice that pcmk-1 is OFFLINE for cluster purposes (its pcsd is still active, allowing it to receive pcs commands, but it is not participating in the cluster).

Also notice that ClusterIP is now running on pcmk-2 — failover happened automatically, and no errors are reported.

Quorum

If a cluster splits into two (or more) groups of nodes that can no longer communicate with each other (aka. partitions), quorum is used to prevent resources from starting on more nodes than desired, which would risk data corruption.

A cluster has quorum when more than half of all known nodes are online in the same partition, or for the mathematically inclined, whenever the following equation is true:

total_nodes < 2 * active_nodes

For example, if a 5-node cluster split into 3- and 2-node paritions, the 3-node partition would have quorum and could continue serving resources. If a 6-node cluster split into two 3-node partitions, neither partition would have quorum; pacemaker’s default behavior in such cases is to stop all resources, in order to prevent data corruption.

Two-node clusters are a special case. By the above definition, a two-node cluster would only have quorum when both nodes are running. This would make the creation of a two-node cluster pointless, but corosync has the ability to treat two-node clusters as if only one node is required for quorum.

The pcs cluster setup command will automatically configure two_node: 1 in corosync.conf, so a two-node cluster will "just work".

If you are using a different cluster shell, you will have to configure corosync.conf appropriately yourself.

Now, simulate node recovery by restarting the cluster stack on pcmk-1, and check the cluster’s status. (It may take a little while before the cluster gets going on the node, but it eventually will look like the below.)

[root@pcmk-1 ~]# pcs cluster start pcmk-1
pcmk-1: Starting Cluster...
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 17:00:04 2018
Last change: Mon Sep 10 16:53:42 2018 by root via cibadmin on pcmk-1

2 nodes configured
1 resource configured

Online: [ pcmk-1 pcmk-2 ]

Full list of resources:

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-2

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

5.4. Prevent Resources from Moving after Recovery

In most circumstances, it is highly desirable to prevent healthy resources from being moved around the cluster. Moving resources almost always requires a period of downtime. For complex services such as databases, this period can be quite long.

To address this, Pacemaker has the concept of resource stickiness, which controls how strongly a service prefers to stay running where it is. You may like to think of it as the "cost" of any downtime. By default, Pacemaker assumes there is zero cost associated with moving resources and will do so to achieve "optimal" ^[6] resource placement. We can specify a different stickiness for every resource, but it is often sufficient to change the default.

[root@pcmk-1 ~]# pcs resource defaults resource-stickiness=100
Warning: Defaults do not apply to resources which override them with their own defined values
[root@pcmk-1 ~]# pcs resource defaults
resource-stickiness: 100

^[5] If the data is corrupt, there is little point in continuing to make it available

^[6] Pacemaker’s definition of optimal may not always agree with that of a human’s. The order in which Pacemaker processes lists of resources and nodes creates implicit preferences in situations where the administrator has not explicitly specified them.

Chapter 6. Add Apache HTTP Server as a Cluster Service

Table of Contents

6.1. Install Apache
6.2. Create Website Documents
6.3. Enable the Apache status URL
6.4. Configure the Cluster
6.5. Ensure Resources Run on the Same Host
6.6. Ensure Resources Start and Stop in Order
6.7. Prefer One Node Over Another
6.8. Move Resources Manually

Now that we have a basic but functional active/passive two-node cluster, we’re ready to add some real services. We’re going to start with Apache HTTP Server because it is a feature of many clusters and relatively simple to configure.

6.1. Install Apache

Before continuing, we need to make sure Apache is installed on both hosts. We also need the wget tool in order for the cluster to be able to check the status of the Apache server.

# yum install -y httpd wget
# firewall-cmd --permanent --add-service=http
# firewall-cmd --reload

Important

Do not enable the httpd service. Services that are intended to be managed via the cluster software should never be managed by the OS. It is often useful, however, to manually start the service, verify that it works, then stop it again, before adding it to the cluster. This allows you to resolve any non-cluster-related problems before continuing. Since this is a simple example, we’ll skip that step here.

6.2. Create Website Documents

We need to create a page for Apache to serve. On CentOS 7.5, the default Apache document root is /var/www/html, so we’ll create an index file there. For the moment, we will simplify things by serving a static site and manually synchronizing the data between the two nodes, so run this command on both nodes:

# cat <<-END >/var/www/html/index.html
 <html>
 <body>My Test Site - $(hostname)</body>
 </html>
END

6.3. Enable the Apache status URL

In order to monitor the health of your Apache instance, and recover it if it fails, the resource agent used by Pacemaker assumes the server-status URL is available. On both nodes, enable the URL with:

# cat <<-END >/etc/httpd/conf.d/status.conf
 <Location /server-status>
    SetHandler server-status
    Require local
 </Location>
END

Note

If you are using a different operating system, server-status may already be enabled or may be configurable in a different location. If you are using a version of Apache HTTP Server less than 2.4, the syntax will be different.

6.4. Configure the Cluster

At this point, Apache is ready to go, and all that needs to be done is to add it to the cluster. Let’s call the resource WebSite. We need to use an OCF resource script called apache in the heartbeat namespace. ^[7] The script’s only required parameter is the path to the main Apache configuration file, and we’ll tell the cluster to check once a minute that Apache is still running.

[root@pcmk-1 ~]# pcs resource create WebSite ocf:heartbeat:apache  \
      configfile=/etc/httpd/conf/httpd.conf \
      statusurl="http://localhost/server-status" \
      op monitor interval=1min

By default, the operation timeout for all resources' start, stop, and monitor operations is 20 seconds. In many cases, this timeout period is less than a particular resource’s advised timeout period. For the purposes of this tutorial, we will adjust the global operation timeout default to 240 seconds.

[root@pcmk-1 ~]# pcs resource op defaults timeout=240s
Warning: Defaults do not apply to resources which override them with their own defined values
[root@pcmk-1 ~]# pcs resource op defaults
timeout: 240s

Note

In a production cluster, it is usually better to adjust each resource’s start, stop, and monitor timeouts to values that are appropriate to the behavior observed in your environment, rather than adjust the global default.

After a short delay, we should see the cluster start Apache.

[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 17:06:22 2018
Last change: Mon Sep 10 17:05:41 2018 by root via cibadmin on pcmk-1

2 nodes configured
2 resources configured

Online: [ pcmk-1 pcmk-2 ]

Full list of resources:

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-2
 WebSite        (ocf::heartbeat:apache):        Started pcmk-1

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

Wait a moment, the WebSite resource isn’t running on the same host as our IP address!

Note

If, in the pcs status output, you see the WebSite resource has failed to start, then you’ve likely not enabled the status URL correctly. You can check whether this is the problem by running:

wget -O - http://localhost/server-status

If you see Not Found or Forbidden in the output, then this is likely the problem. Ensure that the <Location /server-status> block is correct.

6.5. Ensure Resources Run on the Same Host

To reduce the load on any one machine, Pacemaker will generally try to spread the configured resources across the cluster nodes. However, we can tell the cluster that two resources are related and need to run on the same host (or not at all). Here, we instruct the cluster that WebSite can only run on the host that ClusterIP is active on.

To achieve this, we use a colocation constraint that indicates it is mandatory for WebSite to run on the same node as ClusterIP. The "mandatory" part of the colocation constraint is indicated by using a score of INFINITY. The INFINITY score also means that if ClusterIP is not active anywhere, WebSite will not be permitted to run.

Note

If ClusterIP is not active anywhere, WebSite will not be permitted to run anywhere.

Important

Colocation constraints are "directional", in that they imply certain things about the order in which the two resources will have a location chosen. In this case, we’re saying that WebSite needs to be placed on the same machine as ClusterIP, which implies that the cluster must know the location of ClusterIP before choosing a location for WebSite.

[root@pcmk-1 ~]# pcs constraint colocation add WebSite with ClusterIP INFINITY
[root@pcmk-1 ~]# pcs constraint
Location Constraints:
Ordering Constraints:
Colocation Constraints:
  WebSite with ClusterIP (score:INFINITY)
Ticket Constraints:
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 17:08:54 2018
Last change: Mon Sep 10 17:08:27 2018 by root via cibadmin on pcmk-1

2 nodes configured
2 resources configured

Online: [ pcmk-1 pcmk-2 ]

Full list of resources:

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-2
 WebSite        (ocf::heartbeat:apache):        Started pcmk-2

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

6.6. Ensure Resources Start and Stop in Order

Like many services, Apache can be configured to bind to specific IP addresses on a host or to the wildcard IP address. If Apache binds to the wildcard, it doesn’t matter whether an IP address is added before or after Apache starts; Apache will respond on that IP just the same. However, if Apache binds only to certain IP address(es), the order matters: If the address is added after Apache starts, Apache won’t respond on that address.

To be sure our WebSite responds regardless of Apache’s address configuration, we need to make sure ClusterIP not only runs on the same node, but starts before WebSite. A colocation constraint only ensures the resources run together, not the order in which they are started and stopped.

We do this by adding an ordering constraint. By default, all order constraints are mandatory, which means that the recovery of ClusterIP will also trigger the recovery of WebSite.

[root@pcmk-1 ~]# pcs constraint order ClusterIP then WebSite
Adding ClusterIP WebSite (kind: Mandatory) (Options: first-action=start then-action=start)
[root@pcmk-1 ~]# pcs constraint
Location Constraints:
Ordering Constraints:
  start ClusterIP then start WebSite (kind:Mandatory)
Colocation Constraints:
  WebSite with ClusterIP (score:INFINITY)
Ticket Constraints:

6.7. Prefer One Node Over Another

Pacemaker does not rely on any sort of hardware symmetry between nodes, so it may well be that one machine is more powerful than the other.

In such cases, you may want to host the resources on the more powerful node when it is available, to have the best performance — or you may want to host the resources on the less powerful node when it’s available, so you don’t have to worry about whether you can handle the load after a failover.

To do this, we create a location constraint.

In the location constraint below, we are saying the WebSite resource prefers the node pcmk-1 with a score of 50. Here, the score indicates how strongly we’d like the resource to run at this location.

[root@pcmk-1 ~]# pcs constraint location WebSite prefers pcmk-1=50
[root@pcmk-1 ~]# pcs constraint
Location Constraints:
  Resource: WebSite
    Enabled on: pcmk-1 (score:50)
Ordering Constraints:
  start ClusterIP then start WebSite (kind:Mandatory)
Colocation Constraints:
  WebSite with ClusterIP (score:INFINITY)
Ticket Constraints:
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 17:21:41 2018
Last change: Mon Sep 10 17:21:14 2018 by root via cibadmin on pcmk-1

2 nodes configured
2 resources configured

Online: [ pcmk-1 pcmk-2 ]

Full list of resources:

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-2
 WebSite        (ocf::heartbeat:apache):        Started pcmk-2

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

Wait a minute, the resources are still on pcmk-2!

Even though WebSite now prefers to run on pcmk-1, that preference is (intentionally) less than the resource stickiness (how much we preferred not to have unnecessary downtime).

To see the current placement scores, you can use a tool called crm_simulate.

[root@pcmk-1 ~]# crm_simulate -sL

Current cluster status:
Online: [ pcmk-1 pcmk-2 ]

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-2
 WebSite        (ocf::heartbeat:apache):        Started pcmk-2

Allocation scores:
native_color: ClusterIP allocation score on pcmk-1: 50
native_color: ClusterIP allocation score on pcmk-2: 200
native_color: WebSite allocation score on pcmk-1: -INFINITY
native_color: WebSite allocation score on pcmk-2: 100

Transition Summary:

6.8. Move Resources Manually

There are always times when an administrator needs to override the cluster and force resources to move to a specific location. In this example, we will force the WebSite to move to pcmk-1.

We will use the pcs resource move command to create a temporary constraint with a score of INFINITY. While we could update our existing constraint, using move allows to easily get rid of the temporary constraint later. If desired, we could even give a lifetime for the constraint, so it would expire automatically — but we don’t that in this example.

[root@pcmk-1 ~]# pcs resource move WebSite pcmk-1
[root@pcmk-1 ~]# pcs constraint
Location Constraints:
  Resource: WebSite
    Enabled on: pcmk-1 (score:50)
    Enabled on: pcmk-1 (score:INFINITY) (role: Started)
Ordering Constraints:
  start ClusterIP then start WebSite (kind:Mandatory)
Colocation Constraints:
  WebSite with ClusterIP (score:INFINITY)
Ticket Constraints:
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 17:28:55 2018
Last change: Mon Sep 10 17:28:27 2018 by root via crm_resource on pcmk-1

2 nodes configured
2 resources configured

Online: [ pcmk-1 pcmk-2 ]

Full list of resources:

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-1
 WebSite        (ocf::heartbeat:apache):        Started pcmk-1

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

Once we’ve finished whatever activity required us to move the resources to pcmk-1 (in our case nothing), we can then allow the cluster to resume normal operation by removing the new constraint. Due to our first location constraint and our default stickiness, the resources will remain on pcmk-1.

We will use the pcs resource clear command, which removes all temporary constraints previously created by pcs resource move or pcs resource ban.

[root@pcmk-1 ~]# pcs resource clear WebSite
[root@pcmk-1 ~]# pcs constraint
Location Constraints:
  Resource: WebSite
    Enabled on: pcmk-1 (score:50)
Ordering Constraints:
  start ClusterIP then start WebSite (kind:Mandatory)
Colocation Constraints:
  WebSite with ClusterIP (score:INFINITY)
Ticket Constraints:

Note that the INFINITY location constraint is now gone. If we check the cluster status, we can also see that (as expected) the resources are still active on pcmk-1.

[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 17:31:47 2018
Last change: Mon Sep 10 17:31:04 2018 by root via crm_resource on pcmk-1

2 nodes configured
2 resources configured

Online: [ pcmk-1 pcmk-2 ]

Full list of resources:

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-1
 WebSite        (ocf::heartbeat:apache):        Started pcmk-1

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

To remove the constraint with the score of 50, we would first get the constraint’s ID using pcs constraint --full, then remove it with pcs constraint remove and the ID. We won’t show those steps here, but feel free to try it on your own, with the help of the pcs man page if necessary.

^[7] Compare the key used here, ocf:heartbeat:apache, with the one we used earlier for the IP address, ocf:heartbeat:IPaddr2

Chapter 7. Replicate Storage Using DRBD

Table of Contents

7.1. Install the DRBD Packages
7.2. Allocate a Disk Volume for DRBD
7.3. Configure DRBD
7.4. Initialize DRBD
7.5. Populate the DRBD Disk
7.6. Configure the Cluster for the DRBD device
7.7. Configure the Cluster for the Filesystem
7.8. Test Cluster Failover

Even if you’re serving up static websites, having to manually synchronize the contents of that website to all the machines in the cluster is not ideal. For dynamic websites, such as a wiki, it’s not even an option. Not everyone care afford network-attached storage, but somehow the data needs to be kept in sync.

Enter DRBD, which can be thought of as network-based RAID-1. ^[8]

7.1. Install the DRBD Packages

DRBD itself is included in the upstream kernel,^[9] but we do need some utilities to use it effectively.

CentOS does not ship these utilities, so we need to enable a third-party repository to get them. Supported packages for many OSes are available from DRBD’s maker LINBIT, but here we’ll use the free ELRepo repository.

On both nodes, import the ELRepo package signing key, and enable the repository:

# rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
# rpm -Uvh http://www.elrepo.org/elrepo-release-7.0-3.el7.elrepo.noarch.rpm
Retrieving http://www.elrepo.org/elrepo-release-7.0-3.el7.elrepo.noarch.rpm
Preparing...                          ################################# [100%]
Updating / installing...
   1:elrepo-release-7.0-3.el7.elrepo  ################################# [100%]

Now, we can install the DRBD kernel module and utilities:

# yum install -y kmod-drbd84 drbd84-utils

DRBD will not be able to run under the default SELinux security policies. If you are familiar with SELinux, you can modify the policies in a more fine-grained manner, but here we will simply exempt DRBD processes from SELinux control:

# semanage permissive -a drbd_t

We will configure DRBD to use port 7789, so allow that port from each host to the other:

[root@pcmk-1 ~]# firewall-cmd --permanent --add-rich-rule='rule family="ipv4" \
    source address="192.168.122.102" port port="7789" protocol="tcp" accept'
success
[root@pcmk-1 ~]# firewall-cmd --reload
success

[root@pcmk-2 ~]# firewall-cmd --permanent --add-rich-rule='rule family="ipv4" \
    source address="192.168.122.101" port port="7789" protocol="tcp" accept'
success
[root@pcmk-2 ~]# firewall-cmd --reload
success

Note

In this example, we have only two nodes, and all network traffic is on the same LAN. In production, it is recommended to use a dedicated, isolated network for cluster-related traffic, so the firewall configuration would likely be different; one approach would be to add the dedicated network interfaces to the trusted zone.

7.2. Allocate a Disk Volume for DRBD

DRBD will need its own block device on each node. This can be a physical disk partition or logical volume, of whatever size you need for your data. For this document, we will use a 512MiB logical volume, which is more than sufficient for a single HTML file and (later) GFS2 metadata.

[root@pcmk-1 ~]# vgdisplay | grep -e Name -e Free
  VG Name               centos_pcmk-1
  Free  PE / Size       255 / 1020.00 MiB
[root@pcmk-1 ~]# lvcreate --name drbd-demo --size 512M centos_pcmk-1
 Logical volume "drbd-demo" created.
[root@pcmk-1 ~]# lvs
  LV        VG            Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  drbd-demo centos_pcmk-1 -wi-a----- 512.00m
  root      centos_pcmk-1 -wi-ao----   3.00g
  swap      centos_pcmk-1 -wi-ao----   1.00g

Repeat for the second node, making sure to use the same size:

[root@pcmk-1 ~]# ssh pcmk-2 -- lvcreate --name drbd-demo --size 512M centos_pcmk-2
 Logical volume "drbd-demo" created.

7.3. Configure DRBD

There is no series of commands for building a DRBD configuration, so simply run this on both nodes to use this sample configuration:

# cat <<END >/etc/drbd.d/wwwdata.res
resource wwwdata {
 protocol C;
 meta-disk internal;
 device /dev/drbd1;
 syncer {
  verify-alg sha1;
 }
 net {
  allow-two-primaries;
 }
 on pcmk-1 {
  disk   /dev/centos_pcmk-1/drbd-demo;
  address  192.168.122.101:7789;
 }
 on pcmk-2 {
  disk   /dev/centos_pcmk-2/drbd-demo;
  address  192.168.122.102:7789;
 }
}
END

Important

Edit the file to use the hostnames, IP addresses and logical volume paths of your nodes if they differ from the ones used in this guide.

Note

Detailed information on the directives used in this configuration (and other alternatives) is available in the DRBD User’s Guide. The allow-two-primaries option would not normally be used in an active/passive cluster. We are adding it here for the convenience of changing to an active/active cluster later.

7.4. Initialize DRBD

With the configuration in place, we can now get DRBD running.

These commands create the local metadata for the DRBD resource, ensure the DRBD kernel module is loaded, and bring up the DRBD resource. Run them on one node:

[root@pcmk-1 ~]# drbdadm create-md wwwdata



















  --==  Thank you for participating in the global usage survey  ==--
The server's response is:

you are the 2147th user to install this version
initializing activity log
initializing bitmap (16 KB) to all zero
Writing meta data...
New drbd meta data block successfully created.
success
[root@pcmk-1 ~]# modprobe drbd
[root@pcmk-1 ~]# drbdadm up wwwdata


















  --==  Thank you for participating in the global usage survey  ==--
The server's response is:

We can confirm DRBD’s status on this node:

[root@pcmk-1 ~]# cat /proc/drbd
version: 8.4.11-1 (api:1/proto:86-101)
GIT-hash: 66145a308421e9c124ec391a7848ac20203bb03c build by mockbuild@, 2018-04-26 12:10:42

 1: cs:WFConnection ro:Secondary/Unknown ds:Inconsistent/DUnknown C r----s
    ns:0 nr:0 dw:0 dr:0 al:8 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:524236

Because we have not yet initialized the data, this node’s data is marked as Inconsistent. Because we have not yet initialized the second node, the local state is WFConnection (waiting for connection), and the partner node’s status is marked as Unknown.

Now, repeat the above commands on the second node, starting with creating wwwdata.res. After giving it time to connect, when we check the status, it shows:

[root@pcmk-2 ~]# cat /proc/drbd
version: 8.4.11-1 (api:1/proto:86-101)
GIT-hash: 66145a308421e9c124ec391a7848ac20203bb03c build by mockbuild@, 2018-04-26 12:10:42

 1: cs:Connected ro:Secondary/Secondary ds:Inconsistent/Inconsistent C r-----
    ns:0 nr:0 dw:0 dr:0 al:8 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:524236

You can see the state has changed to Connected, meaning the two DRBD nodes are communicating properly, and both nodes are in Secondary role with Inconsistent data.

To make the data consistent, we need to tell DRBD which node should be considered to have the correct data. In this case, since we are creating a new resource, both have garbage, so we’ll just pick pcmk-1 and run this command on it:

[root@pcmk-1 ~]# drbdadm primary --force wwwdata

Note

If you are using a different version of DRBD, the required syntax may be different. See the documentation for your version for how to perform these commands.

If we check the status immediately, we’ll see something like this:

[root@pcmk-1 ~]# cat /proc/drbd
version: 8.4.11-1 (api:1/proto:86-101)
GIT-hash: 66145a308421e9c124ec391a7848ac20203bb03c build by mockbuild@, 2018-04-26 12:10:42

 1: cs:SyncSource ro:Primary/Secondary ds:UpToDate/Inconsistent C r-----
    ns:43184 nr:0 dw:0 dr:45312 al:8 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:481052
        [>...................] sync'ed:  8.6% (481052/524236)K
        finish: 0:01:51 speed: 4,316 (4,316) K/sec

We can see that this node has the Primary role, the partner node has the Secondary role, this node’s data is now considered UpToDate, the partner node’s data is still Inconsistent, and a progress bar shows how far along the partner node is in synchronizing the data.

After a while, the sync should finish, and you’ll see something like:

[root@pcmk-1 ~]# cat /proc/drbd
version: 8.4.11-1 (api:1/proto:86-101)
GIT-hash: 66145a308421e9c124ec391a7848ac20203bb03c build by mockbuild@, 2018-04-26 12:10:42

 1: cs:Connected ro:Primary/Secondary ds:UpToDate/UpToDate C r-----
    ns:524236 nr:0 dw:0 dr:526364 al:8 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0

Both sets of data are now UpToDate, and we can proceed to creating and populating a filesystem for our WebSite resource’s documents.

7.5. Populate the DRBD Disk

On the node with the primary role (pcmk-1 in this example), create a filesystem on the DRBD device:

[root@pcmk-1 ~]# mkfs.xfs /dev/drbd1
meta-data=/dev/drbd1             isize=512    agcount=4, agsize=32765 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=131059, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=855, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0

Note

In this example, we create an xfs filesystem with no special options. In a production environment, you should choose a filesystem type and options that are suitable for your application.

Mount the newly created filesystem, populate it with our web document, give it the same SELinux policy as the web document root, then unmount it (the cluster will handle mounting and unmounting it later):

[root@pcmk-1 ~]# mount /dev/drbd1 /mnt
[root@pcmk-1 ~]# cat <<-END >/mnt/index.html
 <html>
  <body>My Test Site - DRBD</body>
 </html>
END
[root@pcmk-1 ~]# chcon -R --reference=/var/www/html /mnt
[root@pcmk-1 ~]# umount /dev/drbd1

7.6. Configure the Cluster for the DRBD device

One handy feature pcs has is the ability to queue up several changes into a file and commit those changes all at once. To do this, start by populating the file with the current raw XML config from the CIB.

[root@pcmk-1 ~]# pcs cluster cib drbd_cfg

Using pcs’s -f option, make changes to the configuration saved in the drbd_cfg file. These changes will not be seen by the cluster until the drbd_cfg file is pushed into the live cluster’s CIB later.

Here, we create a cluster resource for the DRBD device, and an additional clone resource to allow the resource to run on both nodes at the same time.

[root@pcmk-1 ~]# pcs -f drbd_cfg resource create WebData ocf:linbit:drbd \
         drbd_resource=wwwdata op monitor interval=60s
[root@pcmk-1 ~]# pcs -f drbd_cfg resource master WebDataClone WebData \
         master-max=1 master-node-max=1 clone-max=2 clone-node-max=1 \
         notify=true
[root@pcmk-1 ~]# pcs -f drbd_cfg resource show
 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-1
 WebSite        (ocf::heartbeat:apache):        Started pcmk-1
 Master/Slave Set: WebDataClone [WebData]
     Stopped: [ pcmk-1 pcmk-2 ]

After you are satisfied with all the changes, you can commit them all at once by pushing the drbd_cfg file into the live CIB.

[root@pcmk-1 ~]# pcs cluster cib-push drbd_cfg --config
CIB updated

Let’s see what the cluster did with the new configuration:

[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 17:58:07 2018
Last change: Mon Sep 10 17:57:53 2018 by root via cibadmin on pcmk-1

2 nodes configured
4 resources configured

Online: [ pcmk-1 pcmk-2 ]

Full list of resources:

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-1
 WebSite        (ocf::heartbeat:apache):        Started pcmk-1
 Master/Slave Set: WebDataClone [WebData]
     Masters: [ pcmk-1 ]
     Slaves: [ pcmk-2 ]

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

We can see that WebDataClone (our DRBD device) is running as master (DRBD’s primary role) on pcmk-1 and slave (DRBD’s secondary role) on pcmk-2.

Important

The resource agent should load the DRBD module when needed if it’s not already loaded. If that does not happen, configure your operating system to load the module at boot time. For CentOS 7.5, you would run this on both nodes:

# echo drbd >/etc/modules-load.d/drbd.conf

7.7. Configure the Cluster for the Filesystem

Now that we have a working DRBD device, we need to mount its filesystem.

In addition to defining the filesystem, we also need to tell the cluster where it can be located (only on the DRBD Primary) and when it is allowed to start (after the Primary was promoted).

We are going to take a shortcut when creating the resource this time. Instead of explicitly saying we want the ocf:heartbeat:Filesystem script, we are only going to ask for Filesystem. We can do this because we know there is only one resource script named Filesystem available to pacemaker, and that pcs is smart enough to fill in the ocf:heartbeat: portion for us correctly in the configuration. If there were multiple Filesystem scripts from different OCF providers, we would need to specify the exact one we wanted.

Once again, we will queue our changes to a file and then push the new configuration to the cluster as the final step.

[root@pcmk-1 ~]# pcs cluster cib fs_cfg
[root@pcmk-1 ~]# pcs -f fs_cfg resource create WebFS Filesystem \
        device="/dev/drbd1" directory="/var/www/html" fstype="xfs"
Assumed agent name 'ocf:heartbeat:Filesystem' (deduced from 'Filesystem')
[root@pcmk-1 ~]# pcs -f fs_cfg constraint colocation add \
        WebFS with WebDataClone INFINITY with-rsc-role=Master
[root@pcmk-1 ~]# pcs -f fs_cfg constraint order \
        promote WebDataClone then start WebFS
Adding WebDataClone WebFS (kind: Mandatory) (Options: first-action=promote then-action=start)

We also need to tell the cluster that Apache needs to run on the same machine as the filesystem and that it must be active before Apache can start.

[root@pcmk-1 ~]# pcs -f fs_cfg constraint colocation add WebSite with WebFS INFINITY
[root@pcmk-1 ~]# pcs -f fs_cfg constraint order WebFS then WebSite
Adding WebFS WebSite (kind: Mandatory) (Options: first-action=start then-action=start)

Review the updated configuration.

[root@pcmk-1 ~]# pcs -f fs_cfg constraint
Location Constraints:
  Resource: WebSite
    Enabled on: pcmk-1 (score:50)
Ordering Constraints:
  start ClusterIP then start WebSite (kind:Mandatory)
  promote WebDataClone then start WebFS (kind:Mandatory)
  start WebFS then start WebSite (kind:Mandatory)
Colocation Constraints:
  WebSite with ClusterIP (score:INFINITY)
  WebFS with WebDataClone (score:INFINITY) (with-rsc-role:Master)
  WebSite with WebFS (score:INFINITY)
Ticket Constraints:
[root@pcmk-1 ~]# pcs -f fs_cfg resource show
 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-1
 WebSite        (ocf::heartbeat:apache):        Started pcmk-1
 Master/Slave Set: WebDataClone [WebData]
     Masters: [ pcmk-1 ]
     Slaves: [ pcmk-2 ]
 WebFS  (ocf::heartbeat:Filesystem):    Stopped

After reviewing the new configuration, upload it and watch the cluster put it into effect.

[root@pcmk-1 ~]# pcs cluster cib-push fs_cfg --config
CIB updated
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 18:02:24 2018
Last change: Mon Sep 10 18:02:14 2018 by root via cibadmin on pcmk-1

2 nodes configured
5 resources configured

Online: [ pcmk-1 pcmk-2 ]

Full list of resources:

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-1
 WebSite        (ocf::heartbeat:apache):        Started pcmk-1
 Master/Slave Set: WebDataClone [WebData]
     Masters: [ pcmk-1 ]
     Slaves: [ pcmk-2 ]
 WebFS  (ocf::heartbeat:Filesystem):    Started pcmk-1

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

7.8. Test Cluster Failover

Previously, we used pcs cluster stop pcmk-1 to stop all cluster services on pcmk-1, failing over the cluster resources, but there is another way to safely simulate node failure.

We can put the node into standby mode. Nodes in this state continue to run corosync and pacemaker but are not allowed to run resources. Any resources found active there will be moved elsewhere. This feature can be particularly useful when performing system administration tasks such as updating packages used by cluster resources.

Put the active node into standby mode, and observe the cluster move all the resources to the other node. The node’s status will change to indicate that it can no longer host resources, and eventually all the resources will move.

[root@pcmk-1 ~]# pcs cluster standby pcmk-1
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 18:04:22 2018
Last change: Mon Sep 10 18:03:43 2018 by root via cibadmin on pcmk-1

2 nodes configured
5 resources configured

Node pcmk-1: standby
Online: [ pcmk-2 ]

Full list of resources:

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-2
 WebSite        (ocf::heartbeat:apache):        Started pcmk-2
 Master/Slave Set: WebDataClone [WebData]
     Masters: [ pcmk-2 ]
     Stopped: [ pcmk-1 ]
 WebFS  (ocf::heartbeat:Filesystem):    Started pcmk-2

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

Once we’ve done everything we needed to on pcmk-1 (in this case nothing, we just wanted to see the resources move), we can allow the node to be a full cluster member again.

[root@pcmk-1 ~]# pcs cluster unstandby pcmk-1
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-2 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Mon Sep 10 18:05:22 2018
Last change: Mon Sep 10 18:05:21 2018 by root via cibadmin on pcmk-1

2 nodes configured
5 resources configured

Online: [ pcmk-1 pcmk-2 ]

Full list of resources:

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-2
 WebSite        (ocf::heartbeat:apache):        Started pcmk-2
 Master/Slave Set: WebDataClone [WebData]
     Masters: [ pcmk-2 ]
     Slaves: [ pcmk-1 ]
 WebFS  (ocf::heartbeat:Filesystem):    Started pcmk-2

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

Notice that pcmk-1 is back to the Online state, and that the cluster resources stay where they are due to our resource stickiness settings configured earlier.

^[8] See http://www.drbd.org/ for details.

^[9] Since version 2.6.33

Chapter 8. Configure STONITH

Table of Contents

8.1. What is STONITH?
8.2. Choose a STONITH Device
8.3. Configure the Cluster for STONITH
8.4. Example

8.1. What is STONITH?

STONITH (Shoot The Other Node In The Head aka. fencing) protects your data from being corrupted by rogue nodes or unintended concurrent access.

Just because a node is unresponsive doesn’t mean it has stopped accessing your data. The only way to be 100% sure that your data is safe, is to use STONITH to ensure that the node is truly offline before allowing the data to be accessed from another node.

STONITH also has a role to play in the event that a clustered service cannot be stopped. In this case, the cluster uses STONITH to force the whole node offline, thereby making it safe to start the service elsewhere.

8.2. Choose a STONITH Device

It is crucial that your STONITH device can allow the cluster to differentiate between a node failure and a network failure.

A common mistake people make when choosing a STONITH device is to use a remote power switch (such as many on-board IPMI controllers) that shares power with the node it controls. If the power fails in such a case, the cluster cannot be sure whether the node is really offline, or active and suffering from a network fault, so the cluster will stop all resources to avoid a possible split-brain situation.

Likewise, any device that relies on the machine being active (such as SSH-based "devices" sometimes used during testing) is inappropriate.

8.3. Configure the Cluster for STONITH

Install the STONITH agent(s). To see what packages are available, run yum search fence-. Be sure to install the package(s) on all cluster nodes.
Configure the STONITH device itself to be able to fence your nodes and accept fencing requests. This includes any necessary configuration on the device and on the nodes, and any firewall or SELinux changes needed. Test the communication between the device and your nodes.
Find the correct STONITH agent script: pcs stonith list
Find the parameters associated with the device: pcs stonith describe agent_name
Create a local copy of the CIB: pcs cluster cib stonith_cfg
Create the fencing resource: pcs -f stonith_cfg stonith create stonith_id stonith_device_type [stonith_device_options]
Any flags that do not take arguments, such as --ssl, should be passed as ssl=1.
Enable STONITH in the cluster: pcs -f stonith_cfg property set stonith-enabled=true
If the device does not know how to fence nodes based on their uname, you may also need to set the special pcmk_host_map parameter. See man stonithd for details.
If the device does not support the list command, you may also need to set the special pcmk_host_list and/or pcmk_host_check parameters. See man stonithd for details.
If the device does not expect the victim to be specified with the port parameter, you may also need to set the special pcmk_host_argument parameter. See man stonithd for details.
Commit the new configuration: pcs cluster cib-push stonith_cfg
Once the STONITH resource is running, test it (you might want to stop the cluster on that machine first): stonith_admin --reboot nodename

8.4. Example

For this example, assume we have a chassis containing four nodes and an IPMI device active on 10.0.0.1. Following the steps above would go something like this:

Step 1: Install the fence-agents-ipmilan package on both nodes.

Step 2: Configure the IP address, authentication credentials, etc. in the IPMI device itself.

Step 3: Choose the fence_ipmilan STONITH agent.

Step 4: Obtain the agent’s possible parameters:

[root@pcmk-1 ~]# pcs stonith describe fence_ipmilan
fence_ipmilan - Fence agent for IPMI

fence_ipmilan is an I/O Fencing agentwhich can be used with machines controlled by IPMI.This agent calls support software ipmitool (http://ipmitool.sf.net/). WARNING! This fence agent might report success before the node is powered off. You should use -m/method onoff if your fence device works correctly with that option.

Stonith options:
ipport: TCP/UDP port to use for connection with device
hexadecimal_kg: Hexadecimal-encoded Kg key for IPMIv2 authentication
port: IP address or hostname of fencing device (together with --port-as-ip)
inet6_only: Forces agent to use IPv6 addresses only
ipaddr: IP Address or Hostname
passwd_script: Script to retrieve password
method: Method to fence (onoff|cycle)
inet4_only: Forces agent to use IPv4 addresses only
passwd: Login password or passphrase
lanplus: Use Lanplus to improve security of connection
auth: IPMI Lan Auth type.
cipher: Ciphersuite to use (same as ipmitool -C parameter)
target: Bridge IPMI requests to the remote target address
privlvl: Privilege level on IPMI device
timeout: Timeout (sec) for IPMI operation
login: Login Name
verbose: Verbose mode
debug: Write debug information to given file
power_wait: Wait X seconds after issuing ON/OFF
login_timeout: Wait X seconds for cmd prompt after login
delay: Wait X seconds before fencing is started
power_timeout: Test X seconds for status change after ON/OFF
ipmitool_path: Path to ipmitool binary
shell_timeout: Wait X seconds for cmd prompt after issuing command
port_as_ip: Make "port/plug" to be an alias to IP address
retry_on: Count of attempts to retry power on
sudo: Use sudo (without password) when calling 3rd party sotfware.
priority: The priority of the stonith resource. Devices are tried in order of highest priority to lowest.
pcmk_host_map: A mapping of host names to ports numbers for devices that do not support host names. Eg. node1:1;node2:2,3 would tell the cluster to use port 1 for node1 and ports 2 and
3 for node2
pcmk_host_list: A list of machines controlled by this device (Optional unless pcmk_host_check=static-list).
pcmk_host_check: How to determine which machines are controlled by the device. Allowed values: dynamic-list (query the device), static-list (check the pcmk_host_list attribute), none
(assume every device can fence every machine)
pcmk_delay_max: Enable a random delay for stonith actions and specify the maximum of random delay. This prevents double fencing when using slow devices such as sbd. Use this to enable a
random delay for stonith actions. The overall delay is derived from this random delay value adding a static delay so that the sum is kept below the maximum delay.
pcmk_delay_base: Enable a base delay for stonith actions and specify base delay value. This prevents double fencing when different delays are configured on the nodes. Use this to enable
a static delay for stonith actions. The overall delay is derived from a random delay value adding this static delay so that the sum is kept below the maximum delay.
pcmk_action_limit: The maximum number of actions can be performed in parallel on this device Pengine property concurrent-fencing=true needs to be configured first. Then use this to
specify the maximum number of actions can be performed in parallel on this device. -1 is unlimited.

Default operations:
monitor: interval=60s

Step 5: pcs cluster cib stonith_cfg

Step 6: Here are example parameters for creating our STONITH resource:

[root@pcmk-1 ~]# pcs -f stonith_cfg stonith create ipmi-fencing fence_ipmilan \
      pcmk_host_list="pcmk-1 pcmk-2" ipaddr=10.0.0.1 login=testuser \
      passwd=acd123 op monitor interval=60s
[root@pcmk-1 ~]# pcs -f stonith_cfg stonith
 ipmi-fencing   (stonith:fence_ipmilan):        Stopped

Steps 7-10: Enable STONITH in the cluster:

[root@pcmk-1 ~]# pcs -f stonith_cfg property set stonith-enabled=true
[root@pcmk-1 ~]# pcs -f stonith_cfg property
Cluster Properties:
 cluster-infrastructure: corosync
 cluster-name: mycluster
 dc-version: 1.1.18-11.el7_5.3-2b07d5c5a9
 have-watchdog: false
 stonith-enabled: true

Step 11: pcs cluster cib-push stonith_cfg --config

Step 12: Test:

[root@pcmk-1 ~]# pcs cluster stop pcmk-2
[root@pcmk-1 ~]# stonith_admin --reboot pcmk-2

After a successful test, login to any rebooted nodes, and start the cluster (with pcs cluster start).

Chapter 9. Convert Cluster to Active/Active

Table of Contents

9.1. Install Cluster Filesystem Software
9.2. Configure the Cluster for the DLM
9.3. Create and Populate GFS2 Filesystem
9.4. Reconfigure the Cluster for GFS2
9.5. Clone the IP address
9.6. Clone the Filesystem and Apache Resources
9.7. Test Failover

The primary requirement for an Active/Active cluster is that the data required for your services is available, simultaneously, on both machines. Pacemaker makes no requirement on how this is achieved; you could use a SAN if you had one available, but since DRBD supports multiple Primaries, we can continue to use it here.

9.1. Install Cluster Filesystem Software

The only hitch is that we need to use a cluster-aware filesystem. The one we used earlier with DRBD, xfs, is not one of those. Both OCFS2 and GFS2 are supported; here, we will use GFS2.

On both nodes, install the GFS2 command-line utilities and the Distributed Lock Manager (DLM) required by cluster filesystems:

# yum install -y gfs2-utils dlm

9.2. Configure the Cluster for the DLM

The DLM needs to run on both nodes, so we’ll start by creating a resource for it (using the ocf:pacemaker:controld resource script), and clone it:

[root@pcmk-1 ~]# pcs cluster cib dlm_cfg
[root@pcmk-1 ~]# pcs -f dlm_cfg resource create dlm \
        ocf:pacemaker:controld op monitor interval=60s
[root@pcmk-1 ~]# pcs -f dlm_cfg resource clone dlm clone-max=2 clone-node-max=1
[root@pcmk-1 ~]# pcs -f dlm_cfg resource show
 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-1
 WebSite        (ocf::heartbeat:apache):        Started pcmk-1
 Master/Slave Set: WebDataClone [WebData]
     Masters: [ pcmk-1 ]
     Slaves: [ pcmk-2 ]
 WebFS  (ocf::heartbeat:Filesystem):    Started pcmk-1
 Clone Set: dlm-clone [dlm]
     Stopped: [ pcmk-1 pcmk-2 ]

Activate our new configuration, and see how the cluster responds:

[root@pcmk-1 ~]# pcs cluster cib-push dlm_cfg --config
CIB updated
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-1 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Tue Sep 11 10:18:30 2018
Last change: Tue Sep 11 10:16:49 2018 by hacluster via crmd on pcmk-2

2 nodes configured
8 resources configured

Online: [ pcmk-1 pcmk-2 ]

Full list of resources:

 ipmi-fencing   (stonith:fence_ipmilan):        Started pcmk-1
 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-1
 WebSite        (ocf::heartbeat:apache):        Started pcmk-1
 Master/Slave Set: WebDataClone [WebData]
     Masters: [ pcmk-1 ]
     Slaves: [ pcmk-2 ]
 WebFS  (ocf::heartbeat:Filesystem):    Started pcmk-1
 Clone Set: dlm-clone [dlm]
     Started: [ pcmk-1 pcmk-2 ]

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

9.3. Create and Populate GFS2 Filesystem

Before we do anything to the existing partition, we need to make sure it is unmounted. We do this by telling the cluster to stop the WebFS resource. This will ensure that other resources (in our case, Apache) using WebFS are not only stopped, but stopped in the correct order.

[root@pcmk-1 ~]# pcs resource disable WebFS
[root@pcmk-1 ~]# pcs resource
 ClusterIP      (ocf::heartbeat:IPaddr2):       Started pcmk-1
 WebSite        (ocf::heartbeat:apache):        Stopped
 Master/Slave Set: WebDataClone [WebData]
     Masters: [ pcmk-1 ]
     Slaves: [ pcmk-2 ]
 WebFS  (ocf::heartbeat:Filesystem):    Stopped (disabled)
 Clone Set: dlm-clone [dlm]
     Started: [ pcmk-1 pcmk-2 ]

You can see that both Apache and WebFS have been stopped, and that pcmk-1 is the current master for the DRBD device.

Now we can create a new GFS2 filesystem on the DRBD device.

Warning

This will erase all previous content stored on the DRBD device. Ensure you have a copy of any important data.

Important

Run the next command on whichever node has the DRBD Primary role. Otherwise, you will receive the message:

/dev/drbd1: Read-only file system

[root@pcmk-1 ~]# mkfs.gfs2 -p lock_dlm -j 2 -t mycluster:web /dev/drbd1
It appears to contain an existing filesystem (xfs)
This will destroy any data on /dev/drbd1
Are you sure you want to proceed? [y/n] y
Discarding device contents (may take a while on large devices): Done
Adding journals: Done
Building resource groups: Done
Creating quota file: Done
Writing superblock and syncing: Done
Device:                    /dev/drbd1
Block size:                4096
Device size:               0.50 GB (131059 blocks)
Filesystem size:           0.50 GB (131056 blocks)
Journals:                  2
Resource groups:           3
Locking protocol:          "lock_dlm"
Lock table:                "mycluster:web"
UUID:                      0bcbffab-cada-4105-94d1-be8a26669ee0

The mkfs.gfs2 command required a number of additional parameters:

-p lock_dlm specifies that we want to use the kernel’s DLM.
-j 2 indicates that the filesystem should reserve enough space for two journals (one for each node that will access the filesystem).
-t mycluster:web specifies the lock table name. The format for this field is clustername:fsname. For clustername, we need to use the same value we specified originally with pcs cluster setup --name (which is also the value of cluster_name in /etc/corosync/corosync.conf). If you are unsure what your cluster name is, you can look in /etc/corosync/corosync.conf or execute the command pcs cluster corosync pcmk-1 | grep cluster_name.

Now we can (re-)populate the new filesystem with data (web pages). We’ll create yet another variation on our home page.

[root@pcmk-1 ~]# mount /dev/drbd1 /mnt
[root@pcmk-1 ~]# cat <<-END >/mnt/index.html
<html>
<body>My Test Site - GFS2</body>
</html>
END
[root@pcmk-1 ~]# chcon -R --reference=/var/www/html /mnt
[root@pcmk-1 ~]# umount /dev/drbd1
[root@pcmk-1 ~]# drbdadm verify wwwdata

9.4. Reconfigure the Cluster for GFS2

With the WebFS resource stopped, let’s update the configuration.

[root@pcmk-1 ~]# pcs resource show WebFS
 Resource: WebFS (class=ocf provider=heartbeat type=Filesystem)
  Attributes: device=/dev/drbd1 directory=/var/www/html fstype=xfs
  Meta Attrs: target-role=Stopped
  Operations: monitor interval=20 timeout=40 (WebFS-monitor-interval-20)
              notify interval=0s timeout=60 (WebFS-notify-interval-0s)
              start interval=0s timeout=60 (WebFS-start-interval-0s)
              stop interval=0s timeout=60 (WebFS-stop-interval-0s)

The fstype option needs to be updated to gfs2 instead of xfs.

[root@pcmk-1 ~]# pcs resource update WebFS fstype=gfs2
[root@pcmk-1 ~]# pcs resource show WebFS
 Resource: WebFS (class=ocf provider=heartbeat type=Filesystem)
  Attributes: device=/dev/drbd1 directory=/var/www/html fstype=gfs2
  Meta Attrs: target-role=Stopped
  Operations: monitor interval=20 timeout=40 (WebFS-monitor-interval-20)
              notify interval=0s timeout=60 (WebFS-notify-interval-0s)
              start interval=0s timeout=60 (WebFS-start-interval-0s)
              stop interval=0s timeout=60 (WebFS-stop-interval-0s)

GFS2 requires that DLM be running, so we also need to set up new colocation and ordering constraints for it:

[root@pcmk-1 ~]# pcs constraint colocation add WebFS with dlm-clone INFINITY
[root@pcmk-1 ~]# pcs constraint order dlm-clone then WebFS
Adding dlm-clone WebFS (kind: Mandatory) (Options: first-action=start then-action=start)

9.5. Clone the IP address

There’s no point making the services active on both locations if we can’t reach them both, so let’s clone the IP address.

The IPaddr2 resource agent has built-in intelligence for when it is configured as a clone. It will utilize a multicast MAC address to have the local switch send the relevant packets to all nodes in the cluster, together with iptables clusterip rules on the nodes so that any given packet will be grabbed by exactly one node. This will give us a simple but effective form of load-balancing requests between our two nodes.

Let’s start a new config, and clone our IP:

[root@pcmk-1 ~]# pcs cluster cib loadbalance_cfg
[root@pcmk-1 ~]# pcs -f loadbalance_cfg resource clone ClusterIP \
     clone-max=2 clone-node-max=2 globally-unique=true

clone-max=2 tells the resource agent to split packets this many ways. This should equal the number of nodes that can host the IP.
clone-node-max=2 says that one node can run up to 2 instances of the clone. This should also equal the number of nodes that can host the IP, so that if any node goes down, another node can take over the failed node’s "request bucket". Otherwise, requests intended for the failed node would be discarded.
globally-unique=true tells the cluster that one clone isn’t identical to another (each handles a different "bucket"). This also tells the resource agent to insert iptables rules so each host only processes packets in its bucket(s).

Notice that when the ClusterIP becomes a clone, the constraints referencing ClusterIP now reference the clone. This is done automatically by pcs.

[root@pcmk-1 ~]# pcs -f loadbalance_cfg constraint
Location Constraints:
Ordering Constraints:
  start ClusterIP-clone then start WebSite (kind:Mandatory)
  promote WebDataClone then start WebFS (kind:Mandatory)
  start WebFS then start WebSite (kind:Mandatory)
  start dlm-clone then start WebFS (kind:Mandatory)
Colocation Constraints:
  WebSite with ClusterIP-clone (score:INFINITY)
  WebFS with WebDataClone (score:INFINITY) (with-rsc-role:Master)
  WebSite with WebFS (score:INFINITY)
  WebFS with dlm-clone (score:INFINITY)
Ticket Constraints:

Now we must tell the resource how to decide which requests are processed by which hosts. To do this, we specify the clusterip_hash parameter. The value of sourceip means that the source IP address of incoming packets will be hashed; each node will process a certain range of hashes.

[root@pcmk-1 ~]# pcs -f loadbalance_cfg resource update ClusterIP clusterip_hash=sourceip

Load our configuration to the cluster, and see how it responds.

[root@pcmk-1 ~]# pcs cluster cib-push loadbalance_cfg --config
CIB updated
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-1 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Tue Sep 11 10:36:38 2018
Last change: Tue Sep 11 10:36:33 2018 by root via cibadmin on pcmk-1

2 nodes configured
9 resources configured (1 DISABLED)

Online: [ pcmk-1 pcmk-2 ]

Full list of resources:

 ipmi-fencing   (stonith:fence_ipmilan):        Started pcmk-1
 WebSite        (ocf::heartbeat:apache):        Stopped
 Master/Slave Set: WebDataClone [WebData]
     Masters: [ pcmk-1 ]
     Slaves: [ pcmk-2 ]
 WebFS  (ocf::heartbeat:Filesystem):    Stopped (disabled)
 Clone Set: dlm-clone [dlm]
     Started: [ pcmk-1 pcmk-2 ]
 Clone Set: ClusterIP-clone [ClusterIP] (unique)
     ClusterIP:0        (ocf::heartbeat:IPaddr2):       Started pcmk-2
     ClusterIP:1        (ocf::heartbeat:IPaddr2):       Started pcmk-1

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

If desired, you can demonstrate that all request buckets are working by using a tool such as arping from several source hosts to see which host responds to each.

9.6. Clone the Filesystem and Apache Resources

Now that we have a cluster filesystem ready to go, and our nodes can load-balance requests to a shared IP address, we can configure the cluster so both nodes mount the filesystem and respond to web requests.

Clone the filesystem and Apache resources in a new configuration. Notice how pcs automatically updates the relevant constraints again.

[root@pcmk-1 ~]# pcs cluster cib active_cfg
[root@pcmk-1 ~]# pcs -f active_cfg resource clone WebFS
[root@pcmk-1 ~]# pcs -f active_cfg resource clone WebSite
[root@pcmk-1 ~]# pcs -f active_cfg constraint
Location Constraints:
Ordering Constraints:
  start ClusterIP-clone then start WebSite-clone (kind:Mandatory)
  promote WebDataClone then start WebFS-clone (kind:Mandatory)
  start WebFS-clone then start WebSite-clone (kind:Mandatory)
  start dlm-clone then start WebFS-clone (kind:Mandatory)
Colocation Constraints:
  WebSite-clone with ClusterIP-clone (score:INFINITY)
  WebFS-clone with WebDataClone (score:INFINITY) (with-rsc-role:Master)
  WebSite-clone with WebFS-clone (score:INFINITY)
  WebFS-clone with dlm-clone (score:INFINITY)
Ticket Constraints:

Tell the cluster that it is now allowed to promote both instances to be DRBD Primary (aka. master).

[root@pcmk-1 ~]# pcs -f active_cfg resource update WebDataClone master-max=2

Finally, load our configuration to the cluster, and re-enable the WebFS resource (which we disabled earlier).

[root@pcmk-1 ~]# pcs cluster cib-push active_cfg --config
CIB updated
[root@pcmk-1 ~]# pcs resource enable WebFS

After all the processes are started, the status should look similar to this.

[root@pcmk-1 ~]# pcs resource
 Master/Slave Set: WebDataClone [WebData]
     Masters: [ pcmk-1 pcmk-2 ]
 Clone Set: dlm-clone [dlm]
     Started: [ pcmk-1 pcmk-2 ]
 Clone Set: ClusterIP-clone [ClusterIP] (unique)
     ClusterIP:0        (ocf::heartbeat:IPaddr2):       Started pcmk-2
     ClusterIP:1        (ocf::heartbeat:IPaddr2):       Started pcmk-1
 Clone Set: WebFS-clone [WebFS]
     Started: [ pcmk-1 pcmk-2 ]
 Clone Set: WebSite-clone [WebSite]
     Started: [ pcmk-1 pcmk-2 ]

9.7. Test Failover

Testing failover is left as an exercise for the reader. For example, you can put one node into standby mode, use pcs status to confirm that its ClusterIP clone was moved to the other node, and use arping to verify that packets are not being lost from any source host.

Note

You may find that when a failed node rejoins the cluster, both ClusterIP clones stay on one node, due to the resource stickiness. While this works fine, it effectively eliminates load-balancing and returns the cluster to an active-passive setup again. You can avoid this by disabling stickiness for the IP address resource:

[root@pcmk-1 ~]# pcs resource meta ClusterIP resource-stickiness=0

Configuration Recap

Table of Contents

A.1. Final Cluster Configuration

A.2. Node List

A.3. Cluster Options

A.4. Resources

A.4.1. Default Options
A.4.2. Fencing
A.4.3. Service Address
A.4.4. DRBD - Shared Storage
A.4.5. Cluster Filesystem
A.4.6. Apache

A.1. Final Cluster Configuration

[root@pcmk-1 ~]# pcs resource
 Master/Slave Set: WebDataClone [WebData]
     Masters: [ pcmk-1 pcmk-2 ]
 Clone Set: dlm-clone [dlm]
     Started: [ pcmk-1 pcmk-2 ]
 Clone Set: ClusterIP-clone [ClusterIP] (unique)
     ClusterIP:0        (ocf::heartbeat:IPaddr2):       Started pcmk-2
     ClusterIP:1        (ocf::heartbeat:IPaddr2):       Started pcmk-1
 Clone Set: WebFS-clone [WebFS]
     Started: [ pcmk-1 pcmk-2 ]
 Clone Set: WebSite-clone [WebSite]
     Started: [ pcmk-1 pcmk-2 ]

[root@pcmk-1 ~]# pcs resource op defaults
timeout: 240s

[root@pcmk-1 ~]# pcs stonith
 impi-fencing   (stonith:fence_ipmilan): Started pcmk-1

[root@pcmk-1 ~]# pcs constraint
Location Constraints:
Ordering Constraints:
  start ClusterIP-clone then start WebSite-clone (kind:Mandatory)
  promote WebDataClone then start WebFS-clone (kind:Mandatory)
  start WebFS-clone then start WebSite-clone (kind:Mandatory)
  start dlm-clone then start WebFS-clone (kind:Mandatory)
Colocation Constraints:
  WebSite-clone with ClusterIP-clone (score:INFINITY)
  WebFS-clone with WebDataClone (score:INFINITY) (with-rsc-role:Master)
  WebSite-clone with WebFS-clone (score:INFINITY)
  WebFS-clone with dlm-clone (score:INFINITY)
Ticket Constraints:

[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-1 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Tue Sep 11 10:41:53 2018
Last change: Tue Sep 11 10:40:16 2018 by root via cibadmin on pcmk-1

2 nodes configured
11 resources configured

Online: [ pcmk-1 pcmk-2 ]

Full list of resources:

 ipmi-fencing   (stonith:fence_ipmilan):        Started pcmk-1
 Master/Slave Set: WebDataClone [WebData]
     Masters: [ pcmk-1 pcmk-2 ]
 Clone Set: dlm-clone [dlm]
     Started: [ pcmk-1 pcmk-2 ]
 Clone Set: ClusterIP-clone [ClusterIP] (unique)
     ClusterIP:0        (ocf::heartbeat:IPaddr2):       Started pcmk-2
     ClusterIP:1        (ocf::heartbeat:IPaddr2):       Started pcmk-1
 Clone Set: WebFS-clone [WebFS]
     Started: [ pcmk-1 pcmk-2 ]
 Clone Set: WebSite-clone [WebSite]
     Started: [ pcmk-1 pcmk-2 ]

Daemon Status:
  corosync: active/disabled
  pacemaker: active/disabled
  pcsd: active/enabled

[root@pcmk-1 ~]# pcs cluster cib --config

<configuration>
  <crm_config>
    <cluster_property_set id="cib-bootstrap-options">
      <nvpair id="cib-bootstrap-options-have-watchdog" name="have-watchdog" value="false"/>
      <nvpair id="cib-bootstrap-options-dc-version" name="dc-version" value="1.1.18-11.el7_5.3-2b07d5c5a9"/>
      <nvpair id="cib-bootstrap-options-cluster-infrastructure" name="cluster-infrastructure" value="corosync"/>
      <nvpair id="cib-bootstrap-options-cluster-name" name="cluster-name" value="mycluster"/>
      <nvpair id="cib-bootstrap-options-stonith-enabled" name="stonith-enabled" value="true"/>
      <nvpair id="cib-bootstrap-options-last-lrm-refresh" name="last-lrm-refresh" value="1536679009"/>
    </cluster_property_set>
  </crm_config>
  <nodes>
    <node id="1" uname="pcmk-1"/>
    <node id="2" uname="pcmk-2"/>
  </nodes>
  <resources>
    <primitive class="stonith" id="impi-fencing" type="fence_ipmilan">
      <instance_attributes id="impi-fencing-instance_attributes">
        <nvpair id="impi-fencing-instance_attributes-pcmk_host_list" name="pcmk_host_list" value="pcmk-1 pcmk-2"/>
        <nvpair id="impi-fencing-instance_attributes-ipaddr" name="ipaddr" value="10.0.0.1"/>
        <nvpair id="impi-fencing-instance_attributes-login" name="login" value="testuser"/>
        <nvpair id="impi-fencing-instance_attributes-passwd" name="passwd" value="acd123"/>
      </instance_attributes>
      <operations>
        <op id="impi-fencing-interval-60s" interval="60s" name="monitor"/>
      </operations>
    </primitive>
    <master id="WebDataClone">
      <primitive class="ocf" id="WebData" provider="linbit" type="drbd">
        <instance_attributes id="WebData-instance_attributes">
          <nvpair id="WebData-instance_attributes-drbd_resource" name="drbd_resource" value="wwwdata"/>
        </instance_attributes>
        <operations>
          <op id="WebData-demote-interval-0s" interval="0s" name="demote" timeout="90"/>
          <op id="WebData-monitor-interval-60s" interval="60s" name="monitor"/>
          <op id="WebData-notify-interval-0s" interval="0s" name="notify" timeout="90"/>
          <op id="WebData-promote-interval-0s" interval="0s" name="promote" timeout="90"/>
          <op id="WebData-reload-interval-0s" interval="0s" name="reload" timeout="30"/>
          <op id="WebData-start-interval-0s" interval="0s" name="start" timeout="240"/>
          <op id="WebData-stop-interval-0s" interval="0s" name="stop" timeout="100"/>
        </operations>
      </primitive>
      <meta_attributes id="WebDataClone-meta_attributes">
        <nvpair id="WebDataClone-meta_attributes-master-node-max" name="master-node-max" value="1"/>
        <nvpair id="WebDataClone-meta_attributes-clone-max" name="clone-max" value="2"/>
        <nvpair id="WebDataClone-meta_attributes-notify" name="notify" value="true"/>
        <nvpair id="WebDataClone-meta_attributes-master-max" name="master-max" value="2"/>
        <nvpair id="WebDataClone-meta_attributes-clone-node-max" name="clone-node-max" value="1"/>
      </meta_attributes>
    </master>
    <clone id="dlm-clone">
      <primitive class="ocf" id="dlm" provider="pacemaker" type="controld">
        <operations>
          <op id="dlm-monitor-interval-60s" interval="60s" name="monitor"/>
          <op id="dlm-start-interval-0s" interval="0s" name="start" timeout="90"/>
          <op id="dlm-stop-interval-0s" interval="0s" name="stop" timeout="100"/>
        </operations>
      </primitive>
      <meta_attributes id="dlm-clone-meta_attributes">
        <nvpair id="dlm-clone-meta_attributes-clone-max" name="clone-max" value="2"/>
        <nvpair id="dlm-clone-meta_attributes-clone-node-max" name="clone-node-max" value="1"/>
      </meta_attributes>
    </clone>
    <clone id="ClusterIP-clone">
      <primitive class="ocf" id="ClusterIP" provider="heartbeat" type="IPaddr2">
        <instance_attributes id="ClusterIP-instance_attributes">
          <nvpair id="ClusterIP-instance_attributes-cidr_netmask" name="cidr_netmask" value="32"/>
          <nvpair id="ClusterIP-instance_attributes-ip" name="ip" value="192.168.122.120"/>
          <nvpair id="ClusterIP-instance_attributes-clusterip_hash" name="clusterip_hash" value="sourceip"/>
        </instance_attributes>
        <operations>
          <op id="ClusterIP-monitor-interval-30s" interval="30s" name="monitor"/>
          <op id="ClusterIP-start-interval-0s" interval="0s" name="start" timeout="20s"/>
          <op id="ClusterIP-stop-interval-0s" interval="0s" name="stop" timeout="20s"/>
        </operations>
        <meta_attributes id="ClusterIP-meta_attributes">
          <nvpair id="ClusterIP-meta_attributes-resource-stickiness" name="resource-stickiness" value="0"/>
        </meta_attributes>
      </primitive>
      <meta_attributes id="ClusterIP-clone-meta_attributes">
        <nvpair id="ClusterIP-clone-meta_attributes-clone-max" name="clone-max" value="2"/>
        <nvpair id="ClusterIP-clone-meta_attributes-clone-node-max" name="clone-node-max" value="2"/>
        <nvpair id="ClusterIP-clone-meta_attributes-globally-unique" name="globally-unique" value="true"/>
      </meta_attributes>
    </clone>
    <clone id="WebFS-clone">
      <primitive class="ocf" id="WebFS" provider="heartbeat" type="Filesystem">
        <instance_attributes id="WebFS-instance_attributes">
          <nvpair id="WebFS-instance_attributes-device" name="device" value="/dev/drbd1"/>
          <nvpair id="WebFS-instance_attributes-directory" name="directory" value="/var/www/html"/>
          <nvpair id="WebFS-instance_attributes-fstype" name="fstype" value="gfs2"/>
        </instance_attributes>
        <operations>
          <op id="WebFS-monitor-interval-20" interval="20" name="monitor" timeout="40"/>
          <op id="WebFS-notify-interval-0s" interval="0s" name="notify" timeout="60"/>
          <op id="WebFS-start-interval-0s" interval="0s" name="start" timeout="60"/>
          <op id="WebFS-stop-interval-0s" interval="0s" name="stop" timeout="60"/>
        </operations>
      </primitive>
    </clone>
    <clone id="WebSite-clone">
      <primitive class="ocf" id="WebSite" provider="heartbeat" type="apache">
        <instance_attributes id="WebSite-instance_attributes">
          <nvpair id="WebSite-instance_attributes-configfile" name="configfile" value="/etc/httpd/conf/httpd.conf"/>
          <nvpair id="WebSite-instance_attributes-statusurl" name="statusurl" value="http://localhost/server-status"/>
        </instance_attributes>
        <operations>
          <op id="WebSite-monitor-interval-1min" interval="1min" name="monitor"/>
          <op id="WebSite-start-interval-0s" interval="0s" name="start" timeout="40s"/>
          <op id="WebSite-stop-interval-0s" interval="0s" name="stop" timeout="60s"/>
        </operations>
      </primitive>
      <meta_attributes id="WebSite-clone-meta_attributes"/>
    </clone>
  </resources>
  <constraints>
    <rsc_colocation id="colocation-WebSite-ClusterIP-INFINITY" rsc="WebSite-clone" score="INFINITY" with-rsc="ClusterIP-clone"/>
    <rsc_order first="ClusterIP-clone" first-action="start" id="order-ClusterIP-WebSite-mandatory" then="WebSite-clone" then-action="start"/>
    <rsc_colocation id="colocation-WebFS-WebDataClone-INFINITY" rsc="WebFS-clone" score="INFINITY" with-rsc="WebDataClone" with-rsc-role="Master"/>
    <rsc_order first="WebDataClone" first-action="promote" id="order-WebDataClone-WebFS-mandatory" then="WebFS-clone" then-action="start"/>
    <rsc_colocation id="colocation-WebSite-WebFS-INFINITY" rsc="WebSite-clone" score="INFINITY" with-rsc="WebFS-clone"/>
    <rsc_order first="WebFS-clone" first-action="start" id="order-WebFS-WebSite-mandatory" then="WebSite-clone" then-action="start"/>
    <rsc_colocation id="colocation-WebFS-dlm-clone-INFINITY" rsc="WebFS-clone" score="INFINITY" with-rsc="dlm-clone"/>
    <rsc_order first="dlm-clone" first-action="start" id="order-dlm-clone-WebFS-mandatory" then="WebFS-clone" then-action="start"/>
  </constraints>
  <rsc_defaults>
    <meta_attributes id="rsc_defaults-options">
      <nvpair id="rsc_defaults-options-resource-stickiness" name="resource-stickiness" value="100"/>
    </meta_attributes>
  </rsc_defaults>
  <op_defaults>
    <meta_attributes id="op_defaults-options">
      <nvpair id="op_defaults-options-timeout" name="timeout" value="240s"/>
    </meta_attributes>
  </op_defaults>
</configuration>

A.2. Node List

[root@pcmk-1 ~]# pcs status nodes
Pacemaker Nodes:
 Online: pcmk-1 pcmk-2
 Standby:
 Maintenance:
 Offline:
Pacemaker Remote Nodes:
 Online:
 Standby:
 Maintenance:
 Offline:

A.3. Cluster Options

[root@pcmk-1 ~]# pcs property
Cluster Properties:
 cluster-infrastructure: corosync
 cluster-name: mycluster
 dc-version: 1.1.18-11.el7_5.3-2b07d5c5a9
 have-watchdog: false
 last-lrm-refresh: 1536679009
 stonith-enabled: true

The output shows state information automatically obtained about the cluster, including:

cluster-infrastructure - the cluster communications layer in use (heartbeat or corosync)
cluster-name - the cluster name chosen by the administrator when the cluster was created
dc-version - the version (including upstream source-code hash) of Pacemaker used on the Designated Controller, which is the node elected to determine what actions are needed when events occur

The output also shows options set by the administrator that control the way the cluster operates, including:

stonith-enabled=true - whether the cluster is allowed to use STONITH resources

A.4. Resources

A.4.1. Default Options

[root@pcmk-1 ~]# pcs resource defaults
resource-stickiness: 100

This shows cluster option defaults that apply to every resource that does not explicitly set the option itself. Above:

resource-stickiness - Specify the aversion to moving healthy resources to other machines

A.4.2. Fencing

[root@pcmk-1 ~]# pcs stonith show
 ipmi-fencing   (stonith:fence_ipmilan):        Started pcmk-1
[root@pcmk-1 ~]# pcs stonith show ipmi-fencing
 Resource: ipmi-fencing (class=stonith type=fence_ipmilan)
  Attributes: ipaddr="10.0.0.1" login="testuser" passwd="acd123" pcmk_host_list="pcmk-1 pcmk-2"
  Operations: monitor interval=60s (fence-monitor-interval-60s)

A.4.3. Service Address

Users of the services provided by the cluster require an unchanging address with which to access it. Additionally, we cloned the address so it will be active on both nodes. An iptables rule (created as part of the resource agent) is used to ensure that each request only gets processed by one of the two clone instances. The additional meta options tell the cluster that we want two instances of the clone (one "request bucket" for each node) and that if one node fails, then the remaining node should hold both.

[root@pcmk-1 ~]# pcs resource show ClusterIP-clone
 Clone: ClusterIP-clone
  Meta Attrs: clone-max=2 clone-node-max=2 globally-unique=true
  Resource: ClusterIP (class=ocf provider=heartbeat type=IPaddr2)
   Attributes: cidr_netmask=32 ip=192.168.122.120 clusterip_hash=sourceip
   Meta Attrs: resource-stickiness=0
   Operations: monitor interval=30s (ClusterIP-monitor-interval-30s)
               start interval=0s timeout=20s (ClusterIP-start-interval-0s)
               stop interval=0s timeout=20s (ClusterIP-stop-interval-0s)

A.4.4. DRBD - Shared Storage

Here, we define the DRBD service and specify which DRBD resource (from /etc/drbd.d/*.res) it should manage. We make it a master clone resource and, in order to have an active/active setup, allow both instances to be promoted to master at the same time. We also set the notify option so that the cluster will tell DRBD agent when its peer changes state.

[root@pcmk-1 ~]# pcs resource show WebDataClone
 Master: WebDataClone
  Meta Attrs: master-node-max=1 clone-max=2 notify=true master-max=2 clone-node-max=1
  Resource: WebData (class=ocf provider=linbit type=drbd)
   Attributes: drbd_resource=wwwdata
   Operations: demote interval=0s timeout=90 (WebData-demote-interval-0s)
               monitor interval=60s (WebData-monitor-interval-60s)
               notify interval=0s timeout=90 (WebData-notify-interval-0s)
               promote interval=0s timeout=90 (WebData-promote-interval-0s)
               reload interval=0s timeout=30 (WebData-reload-interval-0s)
               start interval=0s timeout=240 (WebData-start-interval-0s)
               stop interval=0s timeout=100 (WebData-stop-interval-0s)
[root@pcmk-1 ~]# pcs constraint ref WebDataClone
Resource: WebDataClone
  colocation-WebFS-WebDataClone-INFINITY
  order-WebDataClone-WebFS-mandatory

A.4.5. Cluster Filesystem

The cluster filesystem ensures that files are read and written correctly. We need to specify the block device (provided by DRBD), where we want it mounted and that we are using GFS2. Again, it is a clone because it is intended to be active on both nodes. The additional constraints ensure that it can only be started on nodes with active DLM and DRBD instances.

[root@pcmk-1 ~]# pcs resource show WebFS-clone
 Clone: WebFS-clone
  Resource: WebFS (class=ocf provider=heartbeat type=Filesystem)
   Attributes: device=/dev/drbd1 directory=/var/www/html fstype=gfs2
   Operations: monitor interval=20 timeout=40 (WebFS-monitor-interval-20)
               notify interval=0s timeout=60 (WebFS-notify-interval-0s)
               start interval=0s timeout=60 (WebFS-start-interval-0s)
               stop interval=0s timeout=60 (WebFS-stop-interval-0s)
[root@pcmk-1 ~]# pcs constraint ref WebFS-clone
Resource: WebFS-clone
  colocation-WebFS-WebDataClone-INFINITY
  colocation-WebSite-WebFS-INFINITY
  colocation-WebFS-dlm-clone-INFINITY
  order-WebDataClone-WebFS-mandatory
  order-WebFS-WebSite-mandatory
  order-dlm-clone-WebFS-mandatory

A.4.6. Apache

Lastly, we have the actual service, Apache. We need only tell the cluster where to find its main configuration file and restrict it to running on nodes that have the required filesystem mounted and the IP address active.

[root@pcmk-1 ~]# pcs resource show WebSite-clone
 Clone: WebSite-clone
  Resource: WebSite (class=ocf provider=heartbeat type=apache)
   Attributes: configfile=/etc/httpd/conf/httpd.conf statusurl=http://localhost/server-status
   Operations: monitor interval=1min (WebSite-monitor-interval-1min)
               start interval=0s timeout=40s (WebSite-start-interval-0s)
               stop interval=0s timeout=60s (WebSite-stop-interval-0s)
[root@pcmk-1 ~]# pcs constraint ref WebSite-clone
Resource: WebSite-clone
  colocation-WebSite-ClusterIP-INFINITY
  colocation-WebSite-WebFS-INFINITY
  order-ClusterIP-WebSite-mandatory
  order-WebFS-WebSite-mandatory

Sample Corosync Configuration

Sample corosync.conf for two-node cluster created by pcs.

totem {
    version: 2
    cluster_name: mycluster
    secauth: off
    transport: udpu
}

nodelist {
    node {
        ring0_addr: pcmk-1
        nodeid: 1
    }

    node {
        ring0_addr: pcmk-2
        nodeid: 2
    }
}

quorum {
    provider: corosync_votequorum
    two_node: 1
}

logging {
    to_logfile: yes
    logfile: /var/log/cluster/corosync.log
    to_syslog: yes
}

Revision History

Revision History

Revision 1-0

Mon May 17 2010

Andrew Beekhof

Import from Pages.app

Revision 2-0

Wed Sep 22 2010

Raoul Scarazzini

Italian translation

Revision 3-0

Wed Feb 9 2011

Andrew Beekhof

Updated for Fedora 13

Revision 4-0

Wed Oct 5 2011

Andrew Beekhof

Update the GFS2 section to use CMAN

Revision 5-0

Fri Feb 10 2012

Andrew Beekhof

Generate docbook content from asciidoc sources

Revision 6-0

Tues July 3 2012

Andrew Beekhof

Updated for Fedora 17

Revision 7-0

Fri Sept 14 2012

David Vossel

Updated for pcs

Revision 8-0

Mon Jan 05 2015

Ken Gaillot

Updated for Fedora 21

Revision 8-1

Thu Jan 08 2015

Ken Gaillot

Minor corrections, plus use include file for intro

Revision 9-0

Fri Aug 14 2015

Ken Gaillot

Update for CentOS 7.1 and leaving firewalld/SELinux enabled

Revision 9-1

Fri Jan 12 2018

Ken Gaillot

Update for CentOS 7.4 with Pacemaker 1.1.16

Revision 9-2

Wed Sep 5 2018

Ken Gaillot

Update for CentOS 7.5 with Pacemaker 1.1.18

Index

Symbols

/server-status, Enable the Apache status URL

A

Apache HTTP Server, Add Apache HTTP Server as a Cluster Service

/server-status, Enable the Apache status URL
Apache resource configuration, Configure the Cluster

Apache resource configuration, Configure the Cluster

C

Creating and Activating a new SSH Key, Configure SSH

D

Domain name (Query), Use Short Node Names
Domain name (Remove from host name), Use Short Node Names

F

feedback

contact information for this manual, We Need Feedback!

N

Nodes

Domain name (Query), Use Short Node Names
Domain name (Remove from host name), Use Short Node Names
short name, Use Short Node Names

S

short name, Use Short Node Names
SSH, Configure SSH