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⁠7.4. Configure the Cluster for DRBD

One handy feature pcs has is the ability to queue up several changes into a file and commit those changes atomically. To do this, start by populating the file with the current raw xml config from the cib. This can be done using the following command. 
# pcs cluster cib drbd_cfg
Now using the pcs -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 on. 
# pcs -f drbd_cfg resource create WebData ocf:linbit:drbd \
         drbd_resource=wwwdata op monitor interval=60s
# pcs -f drbd_cfg resource master WebDataClone WebData \
         master-max=1 master-node-max=1 clone-max=2 clone-node-max=1 \
         notify=true
# pcs -f drbd_cfg resource show
 ClusterIP      (ocf::heartbeat:IPaddr2) Started
 WebSite        (ocf::heartbeat:apache) Started
 Master/Slave Set: WebDataClone [WebData]
     Stopped: [ WebData:0 WebData:1 ]
After you are satisfied with all the changes, you can commit all the changes at once by pushing the drbd_cfg file into the live cib. 
# pcs cluster push cib drbd_cfg
CIB updated

# pcs status

Last updated: Fri Sep 14 12:19:49 2012
Last change: Fri Sep 14 12:19:13 2012 via cibadmin on pcmk-1
Stack: corosync
Current DC: pcmk-2 (2) - partition with quorum
Version: 1.1.8-1.el7-60a19ed12fdb4d5c6a6b6767f52e5391e447fec0
2 Nodes configured, unknown expected votes
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 ]

Note

TODO: Include details on adding a second DRBD resource
Now that DRBD is functioning we can configure a Filesystem resource to use it. In addition to the filesystem’s definition, 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 though. 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 to use.
Once again we will queue up our changes to a file and then push the new configuration to the cluster as the final step. 
# pcs cluster cib fs_cfg
# pcs -f fs_cfg resource create WebFS Filesystem \
         device="/dev/drbd/by-res/wwwdata" directory="/var/www/html" \
         fstype="ext4"
# pcs -f fs_cfg constraint colocation add WebFS WebDataClone INFINITY with-rsc-role=Master
# 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. 
# pcs -f fs_cfg constraint colocation add WebSite WebFS INFINITY
# pcs -f fs_cfg constraint order WebFS then WebSite
Now review the updated configuration. 
# pcs -f fs_cfg constraint
Location Constraints:
Ordering Constraints:
  start ClusterIP then start WebSite
  WebFS then WebSite
  promote WebDataClone then start WebFS
Colocation Constraints:
  WebSite with ClusterIP
  WebFS with WebDataClone (with-rsc-role:Master)
  WebSite with WebFS

# pcs -f fs_cfg resource show
 ClusterIP      (ocf::heartbeat:IPaddr2) Started
 WebSite        (ocf::heartbeat:apache) Started
 Master/Slave Set: WebDataClone [WebData]
     Masters: [ pcmk-1 ]
     Slaves: [ pcmk-2 ]
 WebFS  (ocf::heartbeat:Filesystem) Stopped
After reviewing the new configuration, we again upload it and watch the cluster put it into effect. 
# pcs cluster push cib fs_cfg
CIB updated
# pcs status
 Last updated: Fri Aug 10 12:47:01 2012

 Last change: Fri Aug 10 12:46:55 2012 via cibadmin on pcmk-1
 Stack: corosync
 Current DC: pcmk-1 (1) - partition with quorum
 Version: 1.1.8-1.el7-60a19ed12fdb4d5c6a6b6767f52e5391e447fec0
 2 Nodes configured, unknown expected votes
 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

⁠7.4.1. Testing Migration

We could shut down the active node again, but another way to safely simulate recovery is to put the node into what is called "standby mode". Nodes in this state tell the cluster that they are not allowed to run resources. Any resources found active there will be moved elsewhere. This feature can be particularly useful when updating the resources' packages.
Put the local node into standby mode and observe the cluster move all the resources to the other node. Note also that the node’s status will change to indicate that it can no longer host resources. 
# pcs cluster standby pcmk-1
# pcs status

Last updated: Fri Sep 14 12:41:12 2012
Last change: Fri Sep 14 12:41:08 2012 via crm_attribute on pcmk-1
Stack: corosync
Current DC: pcmk-1 (1) - partition with quorum
Version: 1.1.8-1.el7-60a19ed12fdb4d5c6a6b6767f52e5391e447fec0
2 Nodes configured, unknown expected votes
5 Resources configured.

Node pcmk-1 (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: [ WebData:1 ]
WebFS   (ocf::heartbeat:Filesystem):    Started pcmk-2
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. 
# pcs cluster unstandby pcmk-1
# pcs status

Last updated: Fri Sep 14 12:43:02 2012
Last change: Fri Sep 14 12:42:57 2012 via crm_attribute on pcmk-1
Stack: corosync
Current DC: pcmk-1 (1) - partition with quorum
Version: 1.1.8-1.el7-60a19ed12fdb4d5c6a6b6767f52e5391e447fec0
2 Nodes configured, unknown expected votes
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
Notice that our resource stickiness settings prevent the services from migrating back to pcmk-1.