repmgr: Quickstart guide

repmgr is an open-source tool suite for mananaging replication and failover among multiple PostgreSQL server nodes. It enhances PostgreSQL's built-in hot-standby capabilities with a set of administration tools for monitoring replication, setting up standby servers and performing failover/switchover operations.

This quickstart guide assumes you are familiar with PostgreSQL replication setup and Linux/UNIX system administration. For a more detailed tutorial covering setup on a variety of different systems, see the README.rst file.

Conceptual Overview

repmgr provides two binaries:

• repmgr: a command-line client to manage replication and repmgr configuration
• repmgrd: an optional daemon process which runs on standby nodes to monitor replication and node status

Each PostgreSQL node requires a repmgr.conf configuration file; additionally it must be "registered" using the repmgr command-line client. repmgr stores information about managed nodes in a custom schema on the node's current master database.

Requirements

repmgr works with PostgreSQL 9.0 and later. All server nodes must be running the same PostgreSQL major version, and preferably should be running the same minor version.

repmgr will work on any Linux or UNIX-like environment capable of running PostgreSQL. rsync must also be installed.

Installation

repmgr must be installed on each PostgreSQL server node.

• Packages

• RPM packages for RedHat-based distributions are available from PGDG
• Debian/Ubuntu provide .deb packages.

It is also possible to build .deb packages directly from the repmgr source; see README.rst for further details.

• Source installation

• repmgr source code is hosted at github (https://github.com/2ndQuadrant/repmgr); tar.gz files can be downloaded from https://github.com/2ndQuadrant/repmgr/releases .

  repmgr can be built easily using PGXS:

  sudo make USE_PGXS=1 install
  

Configuration

Server configuration

Password-less SSH logins must be enabled for the database system user (typically postgres) between all server nodes to enable repmgr to copy required files.

PostgreSQL configuration

The master PostgreSQL node needs to be configured for replication with the following settings:

wal_level = 'hot_standby'      # minimal, archive, hot_standby, or logical
archive_mode = on              # allows archiving to be done
archive_command = 'cd .'       # command to use to archive a logfile segment
max_wal_senders = 10           # max number of walsender processes
wal_keep_segments = 5000       # in logfile segments, 16MB each; 0 disables
hot_standby = on               # "on" allows queries during recovery

Note that repmgr expects a default of 5000 wal_keep_segments, although this value can be overridden when executing the repmgr client.

Additionally, repmgr requires a dedicated PostgreSQL superuser account and a database in which to store monitoring and replication data. The repmgr user account will also be used for replication connections from the standby, so a seperate replication user with the REPLICATION privilege is not required. The database can in principle be any database, including the default postgres one, however it's probably advisable to create a dedicated database for repmgr usage.

repmgr configuration

Each PostgreSQL node requires a repmgr.conf configuration file containing identification and database connection information:

cluster=test
node=1
node_name=node1
conninfo='host=repmgr_node1 user=repmgr_usr dbname=repmgr_db'
pg_bindir=/path/to/postgres/bin

• cluster: common name for the replication cluster; this must be the same on all nodes
• node: a unique, abitrary integer identifier
• name: a unique, human-readable name
• conninfo: a standard conninfo string enabling repmgr to connect to the control database; user and name must be the same on all nodes, while other parameters such as port may differ. The host parameter must be a hostname resolvable by all nodes on the cluster.
• pg_bindir: (optional) location of PostgreSQL binaries, if not in the default $PATH

Note that the configuration file should not be stored inside the PostgreSQL data directory. The configuration file can be specified with the -f, --config-file=PATH option and can have any arbitrary name. If no configuration file is specified, repmgr will search for repmgr.conf in the current working directory.

Each node configuration needs to be registered with repmgr, either using the repmgr command line tool, or the repmgrd daemon; for details see below. Details about each node are inserted into the repmgr database (for details see below).

Replication setup and monitoring

For the purposes of this guide, we'll assume the database user will be repmgr_usr and the database will be repmgr_db, and that the following environment variables are set on each node:

• $HOME: the PostgreSQL system user's home directory
• $PGDATA: the PostgreSQL data directory

Master setup

1. Configure PostgreSQL

• create user and database:

  CREATE ROLE repmgr_usr LOGIN SUPERUSER;
  CREATE DATABASE repmgr_db OWNER repmgr_usr;
  

• configure postgresql.conf for replication (see above)

• update pg_hba.conf, e.g.:

  host    repmgr_db       repmgr_usr  192.168.1.0/24         trust
  host    replication     repmgr_usr  192.168.1.0/24         trust
  

Restart the PostgreSQL server after making these changes. 2. Create the repmgr configuration file:

    $ cat $HOME/repmgr/repmgr.conf
    cluster=test
    node=1
    node_name=node1
    conninfo='host=repmgr_node1 user=repmgr_usr dbname=repmgr_db'
    pg_bindir=/path/to/postgres/bin

(For an annotated repmgr.conf file, see repmgr.conf.sample in the repository's root directory).

3. Register the master node with repmgr:

    $ repmgr -f $HOME/repmgr/repmgr.conf --verbose master register
    [2014-07-04 10:43:42] [INFO] repmgr mgr connecting to master database
    [2014-07-04 10:43:42] [INFO] repmgr connected to master, checking its state
    [2014-07-04 10:43:42] [INFO] master register: creating database objects inside the repmgr_test schema
    [2014-07-04 10:43:43] [NOTICE] Master node correctly registered for cluster test with id 1 (conninfo: host=localhost user=repmgr_usr dbname=repmgr_db)
   

Slave/standby setup

1. Use repmgr to clone the master:

    $ repmgr -D $PGDATA -d repmgr_db -U repmgr_usr -R postgres --verbose standby clone 192.168.1.2
    Opening configuration file: ./repmgr.conf
    [2014-07-04 10:49:00] [ERROR] Did not find the configuration file './repmgr.conf', continuing
    [2014-07-04 10:49:00] [INFO] repmgr connecting to master database
    [2014-07-04 10:49:00] [INFO] repmgr connected to master, checking its state
    [2014-07-04 10:49:00] [INFO] Successfully connected to primary. Current installation size is 1807 MB
    [2014-07-04 10:49:00] [NOTICE] Starting backup...
    [2014-07-04 10:49:00] [INFO] creating directory "/path/to/data/"...
    (...)
    [2014-07-04 10:53:19] [NOTICE] Finishing backup...
    NOTICE:  pg_stop_backup complete, all required WAL segments have been archived
    [2014-07-04 10:53:21] [INFO] repmgr requires primary to keep WAL files 0000000100000000000000AD until at least 0000000100000000000000AD
    [2014-07-04 10:53:21] [NOTICE] repmgr standby clone complete
    [2014-07-04 10:53:21] [NOTICE] HINT: You can now start your postgresql server
    [2014-07-04 10:53:21] [NOTICE] for example : /etc/init.d/postgresql start
   

-R is the database system user on the master node. At this point it does not matter if the repmgr.conf file is not found.

This will clone the PostgreSQL database files from the master, including its postgresql.conf and pg_hba.conf files, and additionally automatically create the recovery.conf file containing the correct parameters to start streaming from the primary node.

2. Start the PostgreSQL server

3. Create the repmgr configuration file:

    $ cat $HOME/repmgr/repmgr.conf
    cluster=test
    node=2
    node_name=node2
    conninfo='host=repmgr_node2 user=repmgr_usr dbname=repmgr_db'
    pg_bindir=/path/to/postgres/bin
   

4. Register the master node with repmgr:

    $ repmgr -f $HOME/repmgr/repmgr.conf --verbose standby register
    Opening configuration file: /path/to/repmgr/repmgr.conf
    [2014-07-04 11:48:13] [INFO] repmgr connecting to standby database
    [2014-07-04 11:48:13] [INFO] repmgr connected to standby, checking its state
    [2014-07-04 11:48:13] [INFO] repmgr connecting to master database
    [2014-07-04 11:48:13] [INFO] finding node list for cluster 'test'
    [2014-07-04 11:48:13] [INFO] checking role of cluster node 'host=repmgr_node1 user=repmgr_usr dbname=repmgr_db'
    [2014-07-04 11:48:13] [INFO] repmgr connected to master, checking its state
    [2014-07-04 11:48:13] [INFO] repmgr registering the standby
    [2014-07-04 11:48:13] [INFO] repmgr registering the standby complete
    [2014-07-04 11:48:13] [NOTICE] Standby node correctly registered for cluster test with id 2 (conninfo: host=localhost user=repmgr_usr dbname=repmgr_db)
   

Monitoring

repmgrd is a management and monitoring daemon which runs on standby nodes and which and can automate remote actions. It can be started simply with e.g.:

repmgrd -f $HOME/repmgr/repmgr.conf --verbose > $HOME/repmgr/repmgr.log 2>&1

or alternatively:

repmgrd -f $HOME/repmgr/repmgr.conf --verbose --monitoring-history > $HOME/repmgr/repmgrd.log 2>&1

which will track advance or lag of the replication in every standby in the repl_monitor table.

Example log output:

[2014-07-04 11:55:17] [INFO] repmgrd Connecting to database 'host=localhost user=repmgr_usr dbname=repmgr_db'
[2014-07-04 11:55:17] [INFO] repmgrd Connected to database, checking its state
[2014-07-04 11:55:17] [INFO] repmgrd Connecting to primary for cluster 'test'
[2014-07-04 11:55:17] [INFO] finding node list for cluster 'test'
[2014-07-04 11:55:17] [INFO] checking role of cluster node 'host=repmgr_node1 user=repmgr_usr dbname=repmgr_db'
[2014-07-04 11:55:17] [INFO] repmgrd Checking cluster configuration with schema 'repmgr_test'
[2014-07-04 11:55:17] [INFO] repmgrd Checking node 2 in cluster 'test'
[2014-07-04 11:55:17] [INFO] Reloading configuration file and updating repmgr tables
[2014-07-04 11:55:17] [INFO] repmgrd Starting continuous standby node monitoring

Failover

To promote a standby to master, on the standby execute e.g.:

repmgr -f  $HOME/repmgr/repmgr.conf --verbose standby promote

repmgr will attempt to connect to the current master to verify that it is not available (if it is, repmgr will not promote the standby).

Other standby servers need to be told to follow the new master with:

repmgr -f  $HOME/repmgr/repmgr.conf --verbose standby follow

See file autofailover_quick_setup.rst for details on setting up automated failover.

repmgr database schema

repmgr creates a small schema for its own use in the database specified in each node's conninfo configuration parameter. This database can in principle be any database. The schema name is the global cluster name prefixed with repmgr_, so for the example setup above the schema name is repmgr_test.

The schema contains two tables:

• repl_nodes stores information about all registered servers in the cluster
• repl_monitor stores monitoring information about each node

and one view, repl_status, which summarizes the latest monitoring information for each node.

Further reading

• http://blog.2ndquadrant.com/announcing-repmgr-2-0/
• http://blog.2ndquadrant.com/managing-useful-clusters-repmgr/
• http://blog.2ndquadrant.com/easier_postgresql_90_clusters/