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