repmgr: Replication Manager for PostgreSQL

repmgr is a suite of open-source tools to manage replication and failover within a cluster of PostgreSQL servers. It enhances PostgreSQL's built-in replication capabilities with utilities to set up standby servers, monitor replication, and perform administrative tasks such as failover or switchover operations.

repmgr 4 is a complete rewrite of the existing repmgr codebase.

Supports PostgreSQL 9.5 and later; support for PostgreSQL 9.3 and 9.4 has been dropped. Please continue to use repmgrd 3.x for those versions.

BDR support

repmgr 4 supports monitoring of a two-node BDR 2.0 cluster. PostgreSQL 9.6 is required for BDR 2.0. Note that BDR 2.0 is not publicly available; please contact 2ndQuadrant for details. repmgr 4 will support future public BDR releases.

Overview

The repmgr suite provides two main tools:

• repmgr - a command-line tool used to perform administrative tasks such as:

  • setting up standby servers
  • promoting a standby server to master
  • switching over master and standby servers
  • displaying the status of servers in the replication cluster

• repmgrd is a daemon which actively monitors servers in a replication cluster and performs the following tasks:

  • monitoring and recording replication performance
  • performing failover by detecting failure of the master and promoting the most suitable standby server
  • provide notifications about events in the cluster to a user-defined script which can perform tasks such as sending alerts by email

repmgr supports and enhances PostgreSQL's built-in streaming replication, which provides a single read/write master server and one or more read-only standbys containing near-real time copies of the master server's database.

Concepts

This guide assumes that you are familiar with PostgreSQL administration and streaming replication concepts. For further details on streaming replication, see this link:

https://www.postgresql.org/docs/current/interactive/warm-standby.html#STREAMING-REPLICATION

The following terms are used throughout the repmgr documentation.

• replication cluster

In the repmgr documentation, "replication cluster" refers to the network of PostgreSQL servers connected by streaming replication.

• node

A node is a server within a replication cluster.

• upstream node

This is the node a standby server is connected to; either the master server or in the case of cascading replication, another standby.

• failover

This is the action which occurs if a master server fails and a suitable standby is promoted as the new master. The repmgrd daemon supports automatic failover to minimise downtime.

• switchover

In certain circumstances, such as hardware or operating system maintenance, it's necessary to take a master server offline; in this case a controlled switchover is necessary, whereby a suitable standby is promoted and the existing master removed from the replication cluster in a controlled manner. The repmgr command line client provides this functionality.

repmgr user and metadata

In order to effectively manage a replication cluster, repmgr needs to store information about the servers in the cluster in a dedicated database schema. This schema is automatically by the repmgr extension, which is installed during the first step in initialising a repmgr-administered cluster (repmgr primary register) and contains the following objects:

tables:

• repmgr.events: records events of interest
• repmgr.nodes: connection and status information for each server in the replication cluster
• repmgr.monitor: historical standby monitoring information written by repmgrd XXX not yet implemented

views:

• repmgr.show_nodes: based on the table repl_nodes, additionally showing the name of the server's upstream node
• repmgr.status: when repmgrd's monitoring is enabled, shows current monitoring status for each node XXX not yet implemented

The repmgr metadata schema can be stored in an existing database or in its own dedicated database. Note that the repmgr metadata schema cannot reside on a database server which is not part of the replication cluster managed by repmgr.

A database user must be available for repmgr to access this database and perform necessary changes. This user does not need to be a superuser, however some operations such as initial installation of the repmgr extension will require a superuser connection (this can be specified where required with the command line option --superuser).

Installation

System requirements

repmgr is developed and tested on Linux and OS X, but should work on any UNIX-like system supported by PostgreSQL itself.

repmgr 4 supports PostgreSQL from version 9.5. If you need to using repmgr on earlier versions of PostgreSQL 9.3 or 9.4, please use repmgr 3.3.

All servers in the replication cluster must be running the same major version of PostgreSQL, and we recommend that they also run the same minor version.

The repmgr tools must be installed on each server in the replication cluster.

A dedicated system user for repmgr is not required; as many repmgr and repmgrd actions require direct access to the PostgreSQL data directory, these commands should be executed by the postgres user.

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 (in which case rsync is also required)
• to perform switchover operations
• when executing repmgr cluster matrix and repmgr cluster crosscheck

---

Tip

: We recommend using a session multiplexer utility such as screen or tmux when performing long-running actions (such as cloning a database) on a remote server - this will ensure the repmgr action won't be prematurely terminated if your ssh session to the server is interrupted or closed.

---

Packages

Release tarballs are also available:

https://github.com/2ndQuadrant/repmgr/releases
http://repmgr.org/

Building from source

Simply:

./configure && make install

Ensure pg_config for the target PostgreSQL version is in $PATH.

Reference

repmgr commands

The following commands are available:

repmgr primary register
repmgr primary unregister

repmgr standby clone
repmgr standby register
repmgr standby unregister
repmgr standby promote
repmgr standby follow
repmgr standby switchover

repmgr bdr register
repmgr bdr unregister

repmgr node status
repmgr node check

repmgr cluster show
repmgr cluster matrix
repmgr cluster crosscheck
repmgr cluster event

• primary register

  Registers a primary in a streaming replication cluster, and configures it for use with repmgr. This command needs to be executed before any standby nodes are registered.

  master register can be used as an alias for primary register.

• standby switchover

  ...

  If other standbys (siblings of the promotion candidate) are connected to the demotion candidate, if --siblings-follow is specified repmgr can instruct these to follow the new primary. Note this can only work if the configuration file on each sibling is the same path as specifed in -f/--config-file or -C/--remote-config-file.

• node status

  Displays an overview of a node's basic information and replication status. This command must be run on the local node.

  Sample output (execute repmgr node status):

    Node "node1":
        PostgreSQL version: 10beta1
        Total data size: 30 MB
        Conninfo: host=localhost dbname=repmgr user=repmgr connect_timeout=2
        Role: primary
        WAL archiving: off
        Archive command: (none)
        Replication connections: 2 (of maximal 10)
        Replication slots: 0 (of maximal 10)
        Replication lag: n/a
  

  See repmgr node check to diagnose issues.

• node check

  Performs some health checks on a node from a replication perspective. This command must be run on the local node.

  Sample output (execute repmgr node check):

    Node "node1":
        Server role: OK (node is primary)
        Replication lag: OK (N/A - node is primary)
        WAL archiving: OK (0 pending files)
        Downstream servers: OK (2 of 2 downstream nodes attached)
        Replication slots: OK (node has no replication slots)
  

  Additionally each check can be performed individually by supplying an additional command line parameter, e.g.:

    $ repmgr node check --role
    OK (node is primary)
  

  Parameters for individual checks are as follows:

  • --role: checks if the node has the expected role
  • --replication-lag": checks if the node is lagging by more than replication_lag_warning or replication_lag_critical seconds.
  • --archive-ready: checks for WAL files which have not yet been archived
  • --downstream: checks that the expected downstream nodes are attached
  • --slots: checks there are no inactive replication slots

  Individual checks can also be output in a Nagios-compatible format with the option --nagios.

• cluster show

  Displays information about each active node in the replication cluster. This command polls each registered server and shows its role (primary / standby / bdr) and status. It polls each server directly and can be run on any node in the cluster; this is also useful when analyzing connectivity from a particular node.

  This command requires either a valid repmgr.conf file or a database connection string to one of the registered nodes; no additional arguments are needed.

  Example:

    $ repmgr -f /etc/repmgr.conf cluster show
  
     ID | Name  | Role    | Status    | Upstream | Connection string
    ----+-------+---------+-----------+----------+-----------------------------------------
     1  | node1 | primary | * running |          | host=db_node1 dbname=repmgr user=repmgr
     2  | node2 | standby |   running | node1    | host=db_node2 dbname=repmgr user=repmgr
     3  | node3 | standby |   running | node1    | host=db_node3 dbname=repmgr user=repmgr
  

  To show database connection errors when polling nodes, run the command in --verbose mode.

  The cluster show command accepts an optional parameter --csv, which outputs the replication cluster's status in a simple CSV format, suitable for parsing by scripts:

    $ repmgr -f /etc/repmgr.conf cluster show --csv
    1,-1,-1
    2,0,0
    3,0,1
  

  The columns have following meanings:

    - node ID
    - availability (0 = available, -1 = unavailable)
    - recovery state (0 = not in recovery, 1 = in recovery, -1 = unknown)
  

  Note that the availability is tested by connecting from the node where repmgr cluster show is executed, and does not necessarily imply the node is down. See repmgr cluster matrix and repmgr cluster crosscheck to get a better overviews of connections between nodes.

• cluster matrix and cluster crosscheck

  These commands display connection information for each pair of nodes in the replication cluster.

  • cluster matrix runs a cluster show on each node and arranges the results in a matrix, recording success or failure;

  • cluster crosscheck runs a cluster matrix on each node and combines the results in a single matrix, providing a full overview of connections between all databases in the cluster.

  These commands require a valid repmgr.conf file on each node. Additionally passwordless ssh connections are required between all nodes.

  Example 1 (all nodes up):

    $ repmgr -f /etc/repmgr.conf cluster matrix
  
    Name   | Id |  1 |  2 |  3
    -------+----+----+----+----
     node1 |  1 |  * |  * |  *
     node2 |  2 |  * |  * |  *
     node3 |  3 |  * |  * |  *
  

  Here cluster matrix is sufficient to establish the state of each possible connection.

  Example 2 (node1 and node2 up, node3 down):

    $ repmgr -f /etc/repmgr.conf cluster matrix
  
    Name   | Id |  1 |  2 |  3
    -------+----+----+----+----
     node1 |  1 |  * |  * |  x
     node2 |  2 |  * |  * |  x
     node3 |  3 |  ? |  ? |  ?
  

  Each row corresponds to one server, and indicates the result of testing an outbound connection from that server.

  Since node3 is down, all the entries in its row are filled with "?", meaning that there we cannot test outbound connections.

  The other two nodes are up; the corresponding rows have "x" in the column corresponding to node3, meaning that inbound connections to that node have failed, and "*" in the columns corresponding to node1 and node2, meaning that inbound connections to these nodes have succeeded.

  In this case, cluster crosscheck gives the same result as cluster matrix, because from any functioning node we can observe the same state: node1 and node2 are up, node3 is down.

  Example 3 (all nodes up, firewall dropping packets originating from node1 and directed to port 5432 on node3)

  Running cluster matrix from node1 gives the following output:

    $ repmgr -f /etc/repmgr.conf cluster matrix
  
    Name   | Id |  1 |  2 |  3
    -------+----+----+----+----
     node1 |  1 |  * |  * |  x
     node2 |  2 |  * |  * |  *
     node3 |  3 |  ? |  ? |  ?
  

  (Note this may take some time depending on the connect_timeout setting in the registered node conninfo strings; default is 1 minute which means without modification the above command would take around 2 minutes to run; see comment elsewhere about setting connect_timeout)

  The matrix tells us that we cannot connect from node1 to node3, and that (therefore) we don't know the state of any outbound connection from node3.

  In this case, the cluster crosscheck command is more informative:

    $ repmgr -f /etc/repmgr.conf cluster crosscheck
  
    Name   | Id |  1 |  2 |  3
    -------+----+----+----+----
     node1 |  1 |  * |  * |  x
     node2 |  2 |  * |  * |  *
     node3 |  3 |  * |  * |  *
  

  What happened is that cluster crosscheck merged its own cluster matrix with the cluster matrix output from node2; the latter is able to connect to node3 and therefore determine the state of outbound connections from that node.

• cluster event

  This outputs a formatted list of cluster events, as stored in the repmgr.events table. Output is in reverse chronological order, and can be filtered with the following options:

    * `--all`: outputs all entries
    * `--limit`: set the maximum number of entries to output (default: 20)
    * `--node-id`: restrict entries to node with this ID
    * `--node-name`: restrict entries to node with this name
    * `--event`: filter specific event
  

  Example:

    $ repmgr -f /etc/repmgr.conf cluster event --event=standby_register
     Node ID | Name  | Event            | OK | Timestamp           | Details
    ---------+-------+------------------+----+---------------------+--------------------------------
     3       | node3 | standby_register | t  | 2017-08-17 10:28:55 | standby registration succeeded
     2       | node2 | standby_register | t  | 2017-08-17 10:28:53 | standby registration succeeded
  

Backwards compatibility

repmgr is now implemented as a PostgreSQL extension, and all database objects used by repmgr are stored in a dedicated repmgr schema, rather than repmgr_$cluster_name. Note there is no need to install the extension, this will be done automatically by repmgr primary register.

Metadata tables have been revised and are not backwards-compatible with repmgr 3.x. (however future DDL updates will be easier as they can be carried out via the ALTER EXTENSION mechanism.).

An extension upgrade script will be provided for pre-4.0 installations; note this will require the existing repmgr_$cluster_name schema to be renamed to repmgr beforehand.

Some configuration items have had their names changed for consistency and clarity e.g. node => node_id. repmgr will issue a warning about deprecated/altered options.

Some configuration items have been changed to command line options, and vice-versa, e.g. to avoid hard-coding items such as a a node's upstream ID, which might change over time.

See file doc/changes-in-repmgr4.md for more details.

Generating event notifications with repmgr/repmgrd

Each time repmgr or repmgrd perform a significant event, a record of that event is written into the repmgr.events table together with a timestamp, an indication of failure or success, and further details if appropriate. This is useful for gaining an overview of events affecting the replication cluster. However note that this table has advisory character and should be used in combination with the repmgr and PostgreSQL logs to obtain details of any events.

Example output after a primary was registered and a standby cloned and registered:

repmgr=# SELECT * from repmgr.events ;
 node_id |      event       | successful |        event_timestamp        |                                       details
---------+------------------+------------+-------------------------------+-------------------------------------------------------------------------------------
       1 | primary_register  | t          | 2016-01-08 15:04:39.781733+09 |
       2 | standby_clone    | t          | 2016-01-08 15:04:49.530001+09 | Cloned from host 'repmgr_node1', port 5432; backup method: pg_basebackup; --force: N
       2 | standby_register | t          | 2016-01-08 15:04:50.621292+09 |
(3 rows)

Alternatively use repmgr cluster event to output a list of events.

Additionally, event notifications can be passed to a user-defined program or script which can take further action, e.g. send email notifications. This is done by setting the event_notification_command parameter in repmgr.conf.

This parameter accepts the following format placeholders:

%n - node ID
%e - event type
%s - success (1 or 0)
%t - timestamp
%d - details

The values provided for "%t" and "%d" will probably contain spaces, so should be quoted in the provided command configuration, e.g.:

event_notification_command='/path/to/some/script %n %e %s "%t" "%d"'

Additionally the following format placeholders are available for the event type bdr_failover and optionally bdr_recovery:

%c - conninfo string of the next available node
%a - name of the next available node

These should always be quoted.

By default, all notification type will be passed to the designated script; the notification types can be filtered to explicitly named ones:

event_notifications=primary_register,standby_register

The following event types are available:

• master_register
• standby_register
• standby_unregister
• standby_clone
• standby_promote
• standby_follow
• standby_disconnect_manual
• repmgrd_start
• repmgrd_shutdown
• repmgrd_failover_promote
• repmgrd_failover_follow
• bdr_failover
• bdr_reconnect
• bdr_recovery
• bdr_register
• bdr_unregister

Note that under some circumstances (e.g. no replication cluster master could be located), it will not be possible to write an entry into the repmgr.events table, in which case executing a script via event_notification_command can serve as a fallback by generating some form of notification.

Diagnostics

$ repmgr -f /etc/repmgr.conf node service --list-actions
Following commands would be executed for each action:

    start: "/usr/bin/pg_ctl -l /var/log/postgresql/startup.log -w -D '/var/lib/pgsql/data' start"
     stop: "/usr/bin/pg_ctl -l /var/log/postgresql/startup.log -D '/var/lib/pgsql/data' -m fast -W stop"
  restart: "/usr/bin/pg_ctl -l /var/log/postgresql/startup.log -w -D '/var/lib/pgsql/data' restart"
   reload: "/usr/bin/pg_ctl -l /var/log/postgresql/startup.log -w -D '/var/lib/pgsql/data' reload"
  promote: "/usr/bin/pg_ctl -l /var/log/postgresql/startup.log -w -D '/var/lib/pgsql/data' promote"