In normal operation, repmgrd monitors the state of the PostgreSQL node it is running on, and will take appropriate action if problems are detected, e.g. (if so configured) promote the node to primary, if the existing primary has been determined as failed.
However, repmgrd is unable to distinguish between planned outages (such as performing a switchover or installing PostgreSQL maintenance released), and an actual server outage. In versions prior to repmgr 4.2 it was necessary to stop repmgrd on all nodes (or at least on all nodes where repmgrd is configured for automatic failover) to prevent repmgrd from making unintentional changes to the replication cluster.
From repmgr 4.2, repmgrd can now be "paused", i.e. instructed not to take any action such as performing a failover. This can be done from any node in the cluster, removing the need to stop/restart each repmgrd individually.
Note: For major PostgreSQL upgrades, e.g. from PostgreSQL 10 to PostgreSQL 11, repmgrd should be shut down completely and only started up once the repmgr packages for the new PostgreSQL major version have been installed.
In order to be able to pause/unpause repmgrd, following prerequisites must be met:
Note: These conditions are required for normal repmgr operation in any case.
To pause repmgrd, execute repmgr daemon pause, e.g.:
$ repmgr -f /etc/repmgr.conf daemon pause NOTICE: node 1 (node1) paused NOTICE: node 2 (node2) paused NOTICE: node 3 (node3) paused
The state of repmgrd on each node can be checked with repmgr daemon status, e.g.:
$ repmgr -f /etc/repmgr.conf daemon status ID | Name | Role | Status | repmgrd | PID | Paused? ----+-------+---------+---------+---------+------+--------- 1 | node1 | primary | running | running | 7851 | yes 2 | node2 | standby | running | running | 7889 | yes 3 | node3 | standby | running | running | 7918 | yes
Note: If executing a switchover with repmgr standby switchover, repmgr will automatically pause/unpause repmgrd as part of the switchover process.
If the primary (in this example, node1) is stopped, repmgrd running on one of the standbys (here: node2) will react like this:
[2018-09-20 12:22:21] [WARNING] unable to connect to upstream node "node1" (node ID: 1) [2018-09-20 12:22:21] [INFO] checking state of node 1, 1 of 5 attempts [2018-09-20 12:22:21] [INFO] sleeping 1 seconds until next reconnection attempt ... [2018-09-20 12:22:24] [INFO] sleeping 1 seconds until next reconnection attempt [2018-09-20 12:22:25] [INFO] checking state of node 1, 5 of 5 attempts [2018-09-20 12:22:25] [WARNING] unable to reconnect to node 1 after 5 attempts [2018-09-20 12:22:25] [NOTICE] node is paused [2018-09-20 12:22:33] [INFO] node "node2" (node ID: 2) monitoring upstream node "node1" (node ID: 1) in degraded state [2018-09-20 12:22:33] [DETAIL] repmgrd paused by administrator [2018-09-20 12:22:33] [HINT] execute "repmgr daemon unpause" to resume normal failover mode
If the primary becomes available again (e.g. following a software upgrade), repmgrd will automatically reconnect, e.g.:
[2018-09-20 13:12:41] [NOTICE] reconnected to upstream node 1 after 8 seconds, resuming monitoring
To unpause repmgrd, execute repmgr daemon unpause, e.g.:
$ repmgr -f /etc/repmgr.conf daemon unpause NOTICE: node 1 (node1) unpaused NOTICE: node 2 (node2) unpaused NOTICE: node 3 (node3) unpaused
Note: If the previous primary is no longer accessible when repmgrd is unpaused, no failover action will be taken. Instead, a new primary must be manually promoted using repmgr standby promote, and any standbys attached to the new primary with repmgr standby follow.
This is to prevent repmgr daemon unpause resulting in the automatic promotion of a new primary, which may be a problem particularly in larger clusters, where repmgrd could select a different promotion candidate to the one intended by the administrator.
The pause state of each node will be stored over a PostgreSQL restart.