How to create shared virtual IP using Pacemaker

Shared resources in a cluster need to be accessible via an IP address. For this, we need to create a clustered IP address for our Pacemaker cluster, which will automatically be assigned to one of our cluster nodes at any point in time. Pacemaker will automatically re-assign the IP address to another node in our cluster if anything is wrong with the node currently assigned the IP address.

Shared virtual IP could be created on a Pacemaker cluster using pcs tool at the terminal.

Steps to create floating IP address using Pacemaker:

Install Pacemaker, Corosync and pcs on all of your available nodes.

Related: How to install Pacemaker, Corosync and pcs on CentOS, Red Hat or Fedora
Related: How to install Pacemaker, Corosync and pcs on Ubuntu or Debian
Create a Pacemaker cluster from one of your nodes.

Related: How to create a Pacemaker cluster

Create a cluster IP resource using pcs from one of your cluster nodes.

$ sudo pcs resource create cluster_ip ocf:heartbeat:IPaddr2 ip=192.168.111.10 cidr_netmask=24 op monitor interval=30s

Ping the newly created IP address from all of your cluster nodes.

$ ping -c3 192.168.111.10
PING 192.168.111.10 (192.168.111.10) 56(84) bytes of data.
64 bytes from 192.168.111.10: icmp_seq=1 ttl=64 time=0.054 ms
64 bytes from 192.168.111.10: icmp_seq=2 ttl=64 time=0.086 ms
64 bytes from 192.168.111.10: icmp_seq=3 ttl=64 time=0.048 ms

--- 192.168.111.10 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2000ms
rtt min/avg/max/mdev = 0.048/0.062/0.086/0.019 ms

View details of the created cluster IP resource using pcs from one of your cluster nodes.

$ sudo pcs status resources cluster_ip
 Resource: cluster_ip (class=ocf provider=heartbeat type=IPaddr2)
  Attributes: cidr_netmask=24 ip=192.168.111.10
  Operations: monitor interval=30s (cluster_ip-monitor-interval-30s)
              start interval=0s timeout=20s (cluster_ip-start-interval-0s)
              stop interval=0s timeout=20s (cluster_ip-stop-interval-0s)

View details of cluster and created resources using pcs from one of your cluster nodes.

$ sudo pcs status
Cluster name: clustername
Stack: corosync
Current DC: node-02 (version 1.1.20-5.el7_7.1-3c4c782f70) - partition with quorum
Last updated: Mon Sep 30 05:38:30 2019
Last change: Mon Sep 30 05:31:00 2019 by root via cibadmin on node-01

2 nodes configured
1 resource configured

Online: [ node-01 node-02 ]

Full list of resources:

 cluster_ip	(ocf::heartbeat:IPaddr2):	Started node-01

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

Make sure the status for the pacemaker, corosync and pcsd daemon is enabled. If the status is disabled, re-enable it which is to set the services to automatically start during system boot.

$ sudo systemctl enable pacemaker corosync pcsd
Created symlink from /etc/systemd/system/multi-user.target.wants/pacemaker.service to /usr/lib/systemd/system/pacemaker.service.
Created symlink from /etc/systemd/system/multi-user.target.wants/corosync.service to /usr/lib/systemd/system/corosync.service.
Created symlink from /etc/systemd/system/multi-user.target.wants/pcsd.service to /usr/lib/systemd/system/pcsd.service.

Get the name of the ethernet interface on the node where the cluster_ip resource is started on.

$ ip address show
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: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:0c:29:cd:b0:bc brd ff:ff:ff:ff:ff:ff
    inet 192.168.111.11/24 brd 192.168.111.255 scope global noprefixroute ens33
       valid_lft forever preferred_lft forever
    inet6 fe80::a444:1cd9:da0c:900f/64 scope link tentative noprefixroute dadfailed
       valid_lft forever preferred_lft forever
    inet6 fe80::4f8c:f47a:308c:75af/64 scope link noprefixroute
       valid_lft forever preferred_lft forever

Disable the ethernet interface on the node where the cluster_ip resource is started on to test failover.
```
$ sudo ip link set ens33 down
```
You will be disconnected from the node if you are connecting remotely using ssh via the disabled interface

Check the cluster status on any other node to see if the cluster_ip resource correctly started on another node.

$ sudo pcs status
Cluster name: clustername
Stack: corosync
Current DC: node-02 (version 1.1.20-5.el7_7.1-3c4c782f70) - partition with quorum
Last updated: Wed Oct  2 22:38:57 2019
Last change: Wed Oct  2 22:21:59 2019 by root via cibadmin on node-01

2 nodes configured
1 resource configured

Online: [ node-02 ]
OFFLINE: [ node-01 ]

Full list of resources:

 cluster_ip	(ocf::heartbeat:IPaddr2):	Started node-02

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

The status of the node with disabled ethernet interface should now be OFFLINE .

Ping the cluster_ip's address again to test that the IP address is still reachable.

$ ping -c3 192.168.111.10
PING 192.168.111.10 (192.168.111.10) 56(84) bytes of data.
64 bytes from 192.168.111.10: icmp_seq=1 ttl=64 time=0.059 ms
64 bytes from 192.168.111.10: icmp_seq=2 ttl=64 time=0.076 ms
64 bytes from 192.168.111.10: icmp_seq=3 ttl=64 time=0.061 ms

--- 192.168.111.10 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2000ms
rtt min/avg/max/mdev = 0.059/0.065/0.076/0.011 ms

Re-enable the ethernet interface on the OFFLINE node to for the node to re-join our cluster.
```
$ sudo ip link set ens33 up
```

Re-check if pacemaker, corosync and pcsd services are enabled (to automatically start during system boot) on all nodes.

$ sudo systemctl status pacemaker corosync pcsd | grep Loaded
   Loaded: loaded (/usr/lib/systemd/system/pacemaker.service; disabled; vendor preset: disabled)
   Loaded: loaded (/usr/lib/systemd/system/corosync.service; disabled; vendor preset: disabled)
   Loaded: loaded (/usr/lib/systemd/system/pcsd.service; enabled; vendor preset: disabled)

Certain pcs commands tend to disable previously enabled services. Enable using the following command:

$ sudo systemctl enable pacemaker corosync pcsd
Created symlink from /etc/systemd/system/multi-user.target.wants/pacemaker.service to /usr/lib/systemd/system/pacemaker.service.
Created symlink from /etc/systemd/system/multi-user.target.wants/corosync.service to /usr/lib/systemd/system/corosync.service.
Created symlink from /etc/systemd/system/multi-user.target.wants/pcsd.service to /usr/lib/systemd/system/pcsd.service.

Author: Mohd Shakir Zakaria
Mohd Shakir Zakaria is an experienced cloud architect with a strong development and open-source advocacy background. He boasts multiple certifications in AWS, Red Hat, VMware, ITIL, and Linux, underscoring his expertise in cloud architecture and system administration.

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