# repmgr configuration

## Prerequisites for configuration

Following software must be installed on both servers:

- PostgreSQL

- repmgr

At network level, connections between the PostgreSQL port (default: `5432`) must be possible between all nodes.

Passwordless `SSH` connectivity between all servers in the replication cluster is not required, but is necessary in the following cases:

- if you need &repmgr; to copy configuration files from outside the PostgreSQL data directory (as is the case with e.g. Debian packages); in this case `rsync` must also be installed on all servers.

- to perform switchover operations

- when executing `repmgr cluster matrix` and `repmgr cluster crosscheck`

Consider setting `ConnectTimeout` to a low value in your SSH configuration. This will make it faster to detect any SSH connection errors.

### PostgreSQL configuration for &repmgr;

The following PostgreSQL configuration parameters may need to be changed in order for &repmgr; (and replication itself) to function correctly.

`hot_standby`

  `hot_standby` must always be set to `on`, as &repmgr; needs to be able to connect to each server it manages.

  Note that `hot_standby` defaults to `on` from PostgreSQL 10 and later; in PostgreSQL 9.6 and earlier, the default was `off`.

  PostgreSQL documentation: hot_standby.

`wal_level`

  `wal_level` must be one of `replica` or `logical` (PostgreSQL 9.5 and earlier: one of `hot_standby` or `logical`).

  PostgreSQL documentation: wal_level.

`max_wal_senders`

  `max_wal_senders` must be set to a value of `2` or greater. In general you will need one WAL sender for each standby which will attach to the PostgreSQL instance; additionally &repmgr; will require two free WAL senders in order to clone further standbys.

  `max_wal_senders` should be set to an appropriate value on all PostgreSQL instances in the replication cluster which may potentially become a primary server or (in cascading replication) the upstream server of a standby.

  PostgreSQL documentation: max_wal_senders.

  From PostgreSQL 12, `max_wal_senders` must be set to the same or a higher value as the primary node (at the time the node was cloned), otherwise the standby will refuse to start (unless `hot_standby` is set to `off`, which will prevent the node from accepting queries).

`max_replication_slots`

  If you are intending to use replication slots, `max_replication_slots` must be set to a non-zero value.

  `max_replication_slots` should be set to an appropriate value on all PostgreSQL instances in the replication cluster which may potentially become a primary server or (in cascading replication) the upstream server of a standby.

  PostgreSQL documentation: max_replication_slots.

`wal_log_hints`

  If you are intending to use pg_rewind, and the cluster was not initialised using data checksums, you may want to consider enabling `wal_log_hints`.

  For more details see .

  PostgreSQL documentation: wal_log_hints.

`archive_mode`

  We suggest setting `archive_mode` to `on` (and `archive_command` to `/bin/true`; see below) even if you are currently not planning to use WAL file archiving.

  This will make it simpler to set up WAL file archiving if it is ever required, as changes to `archive_mode` require a full PostgreSQL server restart, while `archive_command` changes can be applied via a normal configuration reload.

  However, &repmgr; itself does not require WAL file archiving.

  PostgreSQL documentation: archive_mode.

`archive_command`

  If you have set `archive_mode` to `on` but are not currently planning to use WAL file archiving, set `archive_command` to a command which does nothing but returns `true`, such as `/bin/true`. See above for details.

  PostgreSQL documentation: archive_command.

`wal_keep_segments` / `wal_keep_size`

  Normally there is no need to set `wal_keep_segments` (PostgreSQL 13 and later: `wal_keep_size`; default: `0`), as it is not a reliable way of ensuring that all required WAL segments are available to standbys. Replication slots and/or an archiving solution such as Barman are recommended to ensure standbys have a reliable source of WAL segments at all times.

  The only reason ever to set `wal_keep_segments` / `wal_keep_size` is you have you have configured `pg_basebackup_options` in `repmgr.conf` to include the setting `--wal-method=fetch` (PostgreSQL 9.6 and earlier: `--xlog-method=fetch`) and you have not set `restore_command` in `repmgr.conf` to fetch WAL files from a reliable source such as Barman, in which case you'll need to set `wal_keep_segments` to a sufficiently high number to ensure that all WAL files required by the standby are retained. However we do not recommend WAL retention in this way.

  PostgreSQL documentation: wal_keep_segments.

See also the PostgreSQL configuration section in the Quick-start guide.

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