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.

Changes in repmgr4 and 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.

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.

To upgrade from repmgr 3.x, both the repmgr metadatabase and all repmgr configuration files need to be converted. This is quite straightforward and scripts are provided to assist with this. See document docs/upgrading-from-repmgr3.md for further details.

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 primary
  • switching over primary 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 primary 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 primary server and one or more read-only standbys containing near-real time copies of the primary 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 primary server or in the case of cascading replication, another standby.

• failover

This is the action which occurs if a primary server fails and a suitable standby is promoted as the new primary. 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 primary server offline; in this case a controlled switchover is necessary, whereby a suitable standby is promoted and the existing primary 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.monitoring_history: historical standby monitoring information written by repmgrd

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.

If upgrading from repmgr 3, please see the separate upgrade guide docs/upgrading-from-repmgr3.md.

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.

Configuration

repmgr and repmgrd use a common configuration file, by default called repmgr.conf (although any name can be used if explicitly specified). repmgr.conf must contain a number of required parameters, including the database connection string for the local node and the location of its data directory; other values will be inferred from defaults if not explicitly supplied. See section repmgr configuration file below for more details.

The configuration file will be searched for in the following locations:

• a configuration file specified by the -f/--config-file command line option
• a location specified by the package maintainer (if repmgr was installed from a package and the package maintainer has specified the configuration file location)
• repmgr.conf in the local directory
• /etc/repmgr.conf
• the directory reported by pg_config --sysconfdir

Note that if a file is explicitly specified with -f/--config-file, an error will be raised if it is not found or not readable and no attempt will be made to check default locations; this is to prevent repmgr unexpectedly reading the wrong file.

For a full list of annotated configuration items, see the file repmgr.conf.sample.

The following parameters in the configuration file can be overridden with command line options:

• log_level with -L/--log-level
• pg_bindir with -b/--pg_bindir

Logging

By default repmgr and repmgrd will log directly to STDERR. For repmgrd we recommend capturing output in a logfile or using your system's log facility; see repmgr.conf.sample for details.

As a command line utility, repmgr will log directly to the console by default. However in some circumstances, such as when repmgr is executed by repmgrd during a failover event, it makes sense to capture repmgr's log output - this can be done by supplying the command-line option --log-to-file to repmgr.

Command line options and environment variables

For some commands, e.g. repmgr standby clone, database connection parameters need to be provided. Like other PostgreSQL utilities, following standard parameters can be used:

• -d/--dbname=DBNAME
• -h/--host=HOSTNAME
• -p/--port=PORT
• -U/--username=USERNAME

If -d/--dbname contains an = sign or starts with a valid URI prefix (postgresql:// or postgres://), it is treated as a conninfo string. See the PostgreSQL documentation for further details:

https://www.postgresql.org/docs/current/static/libpq-connect.html#LIBPQ-CONNSTRING

Note that if a conninfo string is provided, values set in this will override any provided as individual parameters. For example, with -d 'host=foo' --host bar, foo will be chosen over bar.

Like other PostgreSQL utilities, repmgr will default to any values set in environment variables if explicit command line parameters are not provided. See the PostgreSQL documentation for further details:

https://www.postgresql.org/docs/current/static/libpq-envars.html

Setting up a simple replication cluster with repmgr

The following section will describe how to set up a basic replication cluster with a primary and a standby server using the repmgr command line tool. It is assumed PostgreSQL is installed on both servers in the cluster, rsync is available and passwordless SSH connections are possible between both servers.

---

Tip

: for testing repmgr, it's possible to use multiple PostgreSQL instances running on different ports on the same computer, with passwordless SSH access to localhost enabled.

---

PostgreSQL configuration

On the primary server, a PostgreSQL instance must be initialised and running. The following replication settings may need to be adjusted:

# Enable replication connections; set this figure to at least one more
# than the number of standbys which will connect to this server
# (note that repmgr will execute `pg_basebackup` in WAL streaming mode,
# which requires two free WAL senders)

max_wal_senders = 10

# Ensure WAL files contain enough information to enable read-only queries
# on the standby

wal_level = 'hot_standby'

# Enable read-only queries on a standby
# (Note: this will be ignored on a primary but we recommend including
# it anyway)

hot_standby = on

# Enable WAL file archiving
archive_mode = on

# Set archive command to a script or application that will safely store
# you WALs in a secure place. /bin/true is an example of a command that
# ignores archiving. Use something more sensible.
archive_command = '/bin/true'

# If cloning using rsync, or you have configured `pg_basebackup_options`
# in `repmgr.conf` to include the setting `--xlog-method=fetch` (from
# PostgreSQL 10 `--wal-method=fetch`), *and* you have not set
# `restore_command` in `repmgr.conf`to fetch WAL files from another
# source such as Barman, you'll need to set `wal_keep_segments` to a
# high enough value to ensure that all WAL files generated while
# the standby is being cloned are retained until the standby starts up.

# wal_keep_segments = 5000

Monitoring with repmgrd

When repmgrd is running with the option monitoring_history=true, it will constantly write standby node status information to the monitoring_history able, providing a near-real time overview of replication status on all nodes in the cluster.

The view replication_status shows the most recent state for each node, e.g.:

repmgr=# SELECT * FROM repmgr.replication_status;
-[ RECORD 1 ]-------------+-----------------------------
primary_node              | 1
standby_node              | 2
standby_name              | node2
node_type                 | standby
active                    | t
last_monitor_time         | 2016-01-05 14:02:34.51713+09
last_wal_primary_location | 0/3012AF0
last_wal_standby_location | 0/3012AF0
replication_lag           | 0 bytes
replication_time_lag      | 00:00:03.463085
apply_lag                 | 0 bytes
communication_time_lag    | 00:00:00.955385

The interval in which monitoring history is written is controlled by the configuration parameter monitor_interval_secs; default is 2.

As this can generate a large amount of monitoring data in the monitoring_history table , it's advisable to regularly purge historical data with repmgr cluster cleanup; use the -k/--keep-history to specify how many day's worth of data should be retained. XXX not yet implemented

It's possible to use repmgrd to provide monitoring only for some or all nodes by setting failover=manual in the node's repmgr.conf file. In the event of the node's upstream failing, no failover action will be taken and the node will require manual intervention to be reattached to replication. If this occurs, an event notification standby_disconnect_manual will be created.

Note that when a standby node is not streaming directly from its upstream node, e.g. recovering WAL from an archive, apply_lag will always appear as 0 bytes.

XXX ALTER TABLE monitoring_history SET UNLOGGED ;

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.

  primary 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
  

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 formatted 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:

• primary_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 primary 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"