Galera is in failed state (blocked), MySQL server failed to start.

Issue

Galera is in a failed state.

controller-2 ~]$ sudo pcs status
[...]
Online: [ controller-0 controller-1 controller-2 ]
[...]
 Master/Slave Set: galera-master [galera]
     galera     (ocf::heartbeat:galera):        FAILED Master controller-1 (blocked)
     Masters: [ controller-0 controller-2 ]
[...]
Failed Actions:
* galera_promote_0 on controller-1 'unknown error' (1): call=209, status=complete, exitreason='MySQL server failed to start (pid=42507) (rc=0), please check your installation',
    last-rc-change='Wed Feb  5 07:27:30 2020', queued=0ms, exec=4481ms

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