How to set up Dovecot active-active with PCS

A Dovecot active-active deployment keeps IMAP and POP3 access available on multiple nodes so client connections can be spread across servers without relying on a single active instance during maintenance or node failures.

In a Pacemaker cluster managed by pcs, Dovecot can be modeled as a systemd resource and cloned so each node runs its own dovecot.service instance. Pacemaker monitors the unit and restarts it when the service stops, while client traffic distribution stays outside the cluster via a load balancer or DNS.

Service active-active does not replicate mailbox data on its own. Mailbox storage, authentication backends, UID/GID mapping, and TLS material must match across nodes, and shared-storage environments may require Dovecot tuning to reduce index corruption risk before handing start/stop control to the cluster.

Steps to set up Dovecot active-active with PCS:

Confirm the cluster is online with 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
  * Last updated: Thu Jan  1 04:43:11 2026 on node-01
  * Last change:  Thu Jan  1 04:43:09 2026 by root via cibadmin on node-01
  * 3 nodes configured
  * 0 resource instances configured

Node List:
  * Online: [ node-01 node-02 node-03 ]

Full List of Resources:
  * No resources

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

Confirm mailbox storage is shared with a consistent mount path on every node.
```
$ sudo doveconf -n | grep '^mail_location'
mail_location = maildir:/var/vmail/%d/%n
$ findmnt -n /var/vmail
/var/vmail tmpfs  tmpfs  rw,relatime
```
Active-active without shared or replicated mailbox data can present different mailbox state per node and may corrupt Dovecot index files.

Identify the Dovecot service unit name.

$ systemctl list-unit-files --type=service | grep -E '^dovecot\.service'
dovecot.service                              disabled        enabled

Create the Dovecot service resource.

$ sudo pcs resource create dovecot_service systemd:dovecot op monitor interval=30s

Clone the Dovecot service resource across nodes.
```
$ sudo pcs resource clone dovecot_service
```
Related: How to create a cloned resource in Pacemaker
Related: How to set Pacemaker clone resource options

Verify the cloned resource status.

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

Disable automatic dovecot.service startup on each node.

$ sudo systemctl disable dovecot
Synchronizing state of dovecot.service with SysV service script with /usr/lib/systemd/systemd-sysv-install.
Executing: /usr/lib/systemd/systemd-sysv-install disable dovecot
Synchronizing state of dovecot.service with SysV service script with /usr/lib/systemd/systemd-sysv-install.
Executing: /usr/lib/systemd/systemd-sysv-install disable dovecot
Synchronizing state of dovecot.service with SysV service script with /usr/lib/systemd/systemd-sysv-install.
Executing: /usr/lib/systemd/systemd-sysv-install disable dovecot

Pcs-managed starts still work for disabled systemd units.

Confirm Dovecot is listening on expected mail ports on each node.

$ sudo ss -lntp | grep -E ':(143|993|110|995)\b'
LISTEN 0      100          0.0.0.0:995        0.0.0.0:*    users:(("dovecot",pid=184664,fd=23))
LISTEN 0      100          0.0.0.0:993        0.0.0.0:*    users:(("dovecot",pid=184664,fd=38))
LISTEN 0      100          0.0.0.0:143        0.0.0.0:*    users:(("dovecot",pid=184664,fd=37))
LISTEN 0      100          0.0.0.0:110        0.0.0.0:*    users:(("dovecot",pid=184664,fd=22))

Update client routing to distribute traffic across active nodes.

Related: How to plan traffic distribution for active-active PCS services
Run a failover test with client distribution enabled.

Related: How to run a Pacemaker failover test with PCS