How to set up Redis active-active with PCS

Running Redis in an active-active pattern keeps cache endpoints available during node maintenance and allows client traffic to be spread across more than one node instead of relying on a single primary instance.

A Pacemaker cluster managed with pcs controls services as resources, starts and stops them via systemd, and monitors health to restart or recover failed instances. Cloning a resource tells Pacemaker to run the same service on multiple nodes at the same time, with placement rules enforcing limits such as one instance per node.

Cloning a service only manages processes and placement, not data consistency or multi-writer replication. Confirm a Redis design that supports multi-node access (for example Redis Cluster or a vendor active-active implementation), and verify client routing, authentication, persistence, and firewall rules before placing the service under pcs control.

Steps to set up Redis active-active with PCS:

Confirm the cluster is online and has quorum.

$ sudo pcs status
Cluster name: clustername
Cluster Summary:
  * Stack: corosync (Pacemaker is running)
  * Current DC: node-01 (version 2.1.6-6fdc9deea29) - partition with quorum
  * 3 nodes configured
  * 0 resource instances configured
##### snipped #####

Identify the Redis systemd unit name to manage.

$ systemctl list-unit-files --type=service | grep -E '^(redis|redis-server)\.service'
redis-server.service                         disabled        enabled

Stop and disable the Redis unit outside Pacemaker on each node.

$ sudo systemctl disable --now redis-server.service
Synchronizing state of redis-server.service with SysV service script with /usr/lib/systemd/systemd-sysv-install.
Executing: /usr/lib/systemd/systemd-sysv-install disable redis-server
##### snipped #####

Stopping Redis immediately disconnects current clients on that node.

Create the Redis service resource in pcs using the identified unit.
```
$ sudo pcs resource create redis_service systemd:redis-server op monitor interval=30s
```
Use systemd:redis when the unit name is redis.service.

Related: How to create a Pacemaker resource
Clone the Redis service resource across nodes.
```
$ sudo pcs resource clone redis_service
```
Cloning a standalone Redis configuration does not create shared state and can lead to inconsistent keys across nodes.

Related: How to create a cloned resource in Pacemaker
Related: How to set Pacemaker clone resource options

Verify the cloned resource is started on the expected nodes.

$ sudo pcs status resources
  * Clone Set: redis_service-clone [redis_service]:
    * Started: [ node-01 node-02 node-03 ]

Update client routing to distribute traffic across active nodes.

Use a load balancer or DNS strategy that removes unhealthy nodes and matches the chosen Redis topology.

Related: How to plan traffic distribution for active-active PCS services
Verify each active node responds to a basic Redis request.
```
$ redis-cli -h node-01 PING
PONG
$ redis-cli -h node-02 PING
PONG
```
Add -p <port> for a non-default port and -a <password> when authentication is enabled.
Run a failover test after distribution is updated.

Related: How to run a Pacemaker failover test with PCS