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.
The current repmgr version (3.3) supports all PostgreSQL versions from
9.3 to 9.6.
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
-
repmgrdis 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.
For a multi-master replication solution, please see 2ndQuadrant's BDR (bi-directional replication) extension.
http://2ndquadrant.com/en-us/resources/bdr/
For selective replication, e.g. of individual tables or databases from one server to another, please see 2ndQuadrant's pglogical extension.
http://2ndquadrant.com/en-us/resources/pglogical/
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.
witness server
repmgr provides functionality to set up a so-called "witness server" to
assist in determining a new master server in a failover situation with more
than one standby. The witness server itself is not part of the replication
cluster, although it does contain a copy of the repmgr metadata schema
(see below).
The purpose of a witness server is to provide a "casting vote" where servers in the replication cluster are split over more than one location. In the event of a loss of connectivity between locations, the presence or absence of the witness server will decide whether a server at that location is promoted to master; this is to prevent a "split-brain" situation where an isolated location interprets a network outage as a failure of the (remote) master and promotes a (local) standby.
A witness server only needs to be created if repmgrd is in use.
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 created during the first step in initialising
a repmgr-controlled cluster (repmgr master register) and contains the
following objects:
tables:
repl_events: records events of interestrepl_nodes: connection and status information for each server in the replication clusterrepl_monitor: historical standby monitoring information written byrepmgrd
views:
repl_show_nodes: based on the tablerepl_nodes, additionally showing the name of the server's upstream noderepl_status: whenrepmgrd's monitoring is enabled, shows current monitoring status for each node
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 dedicated database superuser is required to own the meta-database as well as carry out administrative actions.
repmgr is developed and tested on Linux and OS X, but should work on any
UNIX-like system supported by PostgreSQL itself.
Current versions of repmgr support PostgreSQL from version 9.3. If you are
interested in using repmgr on earlier versions of PostgreSQL you can download
version 2.1 which supports PostgreSQL from version 9.1.
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
repmgrto copy configuration files from outside the PostgreSQL data directory - when using
rsyncto clone a standby - to perform switchover operations
- when executing
repmgr cluster matrixandrepmgr cluster crosscheck
In these cases rsync is required on all servers too.
TIP: We recommend using a session multiplexer utility such as
screenortmuxwhen performing long-running actions (such as cloning a database) on a remote server - this will ensure therepmgraction won't be prematurely terminated if yoursshsession to the server is interrupted or closed.
We recommend installing repmgr using the available packages for your
system.
-
RedHat/CentOS: RPM packages for
repmgrare available via Yum through the PostgreSQL Global Development Group RPM repository ( http://yum.postgresql.org/ ). Follow the instructions for your distribution (RedHat, CentOS, Fedora, etc.) and architecture as detailed at yum.postgresql.org.2ndQuadrant also provides its own RPM packages which are made available at the same time as each
repmgrrelease, as it can take some days for them to become available via the main PGDG repository. See here for details: -
Debian/Ubuntu: the most recent
repmgrpackages are available from the PostgreSQL Community APT repository ( http://apt.postgresql.org/ ). Instructions can be found in the APT section of the PostgreSQL Wiki ( https://wiki.postgresql.org/wiki/Apt ).
See PACKAGES.md for details on building .deb and .rpm packages from the
repmgr source code.
repmgr source code can be obtained directly from the project GitHub repository:
git clone https://github.com/2ndQuadrant/repmgr
Release tarballs are also available:
https://github.com/2ndQuadrant/repmgr/releases
http://repmgr.org/downloads.php
repmgr is compiled in the same way as a PostgreSQL extension using the PGXS
infrastructure, e.g.:
sudo make USE_PGXS=1 install
repmgr can be built from source in any environment suitable for building
PostgreSQL itself.
repmgr and repmgrd use a common configuration file, by default called
repmgr.conf (although any name can be used if explicitly specified).
At the very least, repmgr.conf must contain the connection parameters
for the local repmgr database; see 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-filecommand line option repmgr.confin 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_levelwith-L/--log-levelpg_bindirwith-b/--pg_bindir
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
(this is a change in behaviour from versions before 3.3, where it would always
log to the same location as repmgrd). 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.
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
The following section will describe how to set up a basic replication cluster
with a master 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 tolocalhostenabled.
On the master 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 master 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
TIP: rather than editing these settings in the default
postgresql.conffile, create a separate file such aspostgresql.replication.confand include it from the end of the main configuration file with:include 'postgresql.replication.conf'
Create a dedicated PostgreSQL superuser account and a database for
the repmgr metadata, e.g.
createuser -s repmgr
createdb repmgr -O repmgr
For the examples in this document, the name repmgr will be used for both
user and database, but any names can be used.
Ensure the repmgr user has appropriate permissions in pg_hba.conf and
can connect in replication mode; pg_hba.conf should contain entries
similar to the following:
local replication repmgr trust
host replication repmgr 127.0.0.1/32 trust
host replication repmgr 192.168.1.0/24 trust
local repmgr repmgr trust
host repmgr repmgr 127.0.0.1/32 trust
host repmgr repmgr 192.168.1.0/24 trust
Adjust according to your network environment and authentication requirements.
On the standby, do not create a PostgreSQL instance, but do ensure an empty
directory is available for the postgres system user to create a data
directory.
Create a repmgr.conf file on the master server. The file must contain at
least the following parameters:
cluster=test
node=1
node_name=node1
conninfo='host=repmgr_node1 user=repmgr dbname=repmgr'
cluster: an arbitrary name for the replication cluster; this must be identical on all nodesnode: a unique integer identifying the node; note this must be a positive 32 bit signed integer between 1 and 2147483647node_name: a unique string identifying the node; we recommend a name specific to the server (e.g. 'server_1'); avoid names indicating the current replication role like 'master' or 'standby' as the server's role could change.conninfo: a valid connection string for therepmgrdatabase on the current server. (On the standby, the database will not yet exist, butrepmgrneeds to know the connection details to complete the setup process).
repmgr.conf should not be stored inside the PostgreSQL data directory,
as it could be overwritten when setting up or reinitialising the PostgreSQL
server. See section Configuration above for further details about repmgr.conf.
repmgr will create a schema named after the cluster and prefixed with repmgr_,
e.g. repmgr_test; we also recommend that you set the repmgr user's search path
to include this schema name, e.g.
ALTER USER repmgr SET search_path TO repmgr_test, "$user", public;
TIP: for Debian-based distributions we recommend explictly setting
pg_bindirto the directory wherepg_ctland other binaries not in the standard path are located. For PostgreSQL 9.5 this would be/usr/lib/postgresql/9.5/bin/.
To enable repmgr to support a replication cluster, the master node must
be registered with repmgr, which creates the repmgr database and adds
a metadata record for the server:
$ repmgr -f repmgr.conf master register
NOTICE: master node correctly registered for cluster test with id 1 (conninfo: host=repmgr_node1 user=repmgr dbname=repmgr)
The metadata record looks like this:
repmgr=# SELECT * FROM repmgr_test.repl_nodes;
id | type | upstream_node_id | cluster | name | conninfo | slot_name | priority | active
----+---------+------------------+---------+-------+---------------------------------------------+-----------+----------+--------
1 | master | | test | node1 | host=repmgr_node1 dbname=repmgr user=repmgr | | 100 | t
(1 row)
Each server in the replication cluster will have its own record and will be updated when its status or role changes.
Create a repmgr.conf file on the standby server. It must contain at
least the same parameters as the master's repmgr.conf, but with
the values node, node_name and conninfo adjusted accordingly, e.g.:
cluster=test
node=2
node_name=node2
conninfo='host=repmgr_node2 user=repmgr dbname=repmgr'
Clone the standby with:
$ repmgr -h repmgr_node1 -U repmgr -d repmgr -D /path/to/node2/data/ -f /etc/repmgr.conf standby clone
NOTICE: destination directory '/path/to/node2/data/' provided
NOTICE: starting backup...
HINT: this may take some time; consider using the -c/--fast-checkpoint option
NOTICE: pg_stop_backup complete, all required WAL segments have been archived
NOTICE: standby clone (using pg_basebackup) complete
NOTICE: you can now start your PostgreSQL server
HINT: for example : pg_ctl -D /path/to/node2/data/ start
This will clone the PostgreSQL data directory files from the master at repmgr_node1
using PostgreSQL's pg_basebackup utility. A recovery.conf file containing the
correct parameters to start streaming from this master server will be created
automatically.
Note that by default, any configuration files in the master's data directory will be
copied to the standby. Typically these will be postgresql.conf, postgresql.auto.conf,
pg_hba.conf and pg_ident.conf. These may require modification before the standby
is started so it functions as desired.
In some cases (e.g. on Debian or Ubuntu Linux installations), PostgreSQL's
configuration files are located outside of the data directory and will
not be copied by default. repmgr can copy these files, either to the same
location on the standby server (provided appropriate directory and file permissions
are available), or into the standby's data directory. This requires passwordless
SSH access to the master server. Add the option --copy-external-config-files
to the repmgr standby clone command; by default files will be copied to
the same path as on the upstream server. To have them placed in the standby's
data directory, specify --copy-external-config-files=pgdata, but note that
any include directives in the copied files may need to be updated.
Caveat: when copying external configuration files: repmgr will only be able
to detect files which contain active settings. If a file is referenced by
an include directive but is empty, only contains comments or contains
settings which have not been activated, the file will not be copied.
TIP: for reliable configuration file management we recommend using a configuration management tool such as Ansible, Chef, Puppet or Salt.
Be aware that when initially cloning a standby, you will need to ensure
that all required WAL files remain available while the cloning is taking
place. To ensure this happens when using the default pg_basebackup method,
repmgr will set pg_basebackup's --xlog-method parameter to stream,
which will ensure all WAL files generated during the cloning process are
streamed in parallel with the main backup. Note that this requires two
replication connections to be available (repmgr will verify sufficient
connections are available before attempting to clone).
To override this behaviour, in repmgr.conf set pg_basebackup's
--xlog-method parameter to fetch:
pg_basebackup_options='--xlog-method=fetch'
and ensure that wal_keep_segments is set to an appropriately high value.
See the pg_basebackup documentation for details:
https://www.postgresql.org/docs/current/static/app-pgbasebackup.html
NOTE: From PostgreSQL 10,
pg_basebackup's--xlog-methodparameter has been renamed to--wal-method.
Make any adjustments to the standby's PostgreSQL configuration files now, then start the server.
NOTE:
repmgr standby clonedoes not requirerepmgr.conf, however we recommend providing this asrepmgrwill set theapplication_nameparameter inrecovery.confas the value provided innode_name, making it easier to identify the node inpg_stat_replication. It's also possible to provide some advanced options for controlling the standby cloning process; see next section for details.
Connect to the master server and execute:
repmgr=# SELECT * FROM pg_stat_replication;
-[ RECORD 1 ]----+------------------------------
pid | 7704
usesysid | 16384
usename | repmgr
application_name | node2
client_addr | 192.168.1.2
client_hostname |
client_port | 46196
backend_start | 2016-01-07 17:32:58.322373+09
backend_xmin |
state | streaming
sent_location | 0/3000220
write_location | 0/3000220
flush_location | 0/3000220
replay_location | 0/3000220
sync_priority | 0
sync_state | async
Register the standby server with:
$ repmgr -f /etc/repmgr.conf standby register
NOTICE: standby node correctly registered for cluster test with id 2 (conninfo: host=repmgr_node2 user=repmgr dbname=repmgr)
Connect to the standby server's repmgr database and check the repl_nodes
table:
repmgr=# SELECT * FROM repmgr_test.repl_nodes ORDER BY id;
id | type | upstream_node_id | cluster | name | conninfo | slot_name | priority | active
----+---------+------------------+---------+-------+---------------------------------------------+-----------+----------+--------
1 | master | | test | node1 | host=repmgr_node1 dbname=repmgr user=repmgr | | 100 | t
2 | standby | 1 | test | node2 | host=repmgr_node2 dbname=repmgr user=repmgr | | 100 | t
(2 rows)
The standby server now has a copy of the records for all servers in the
replication cluster. Note that the relationship between master and standby is
explicitly defined via the upstream_node_id value, which shows here that the
standby's upstream server is the replication cluster master. While of limited
use in a simple master/standby replication cluster, this information is required
to effectively manage cascading replication (see below).
TIP: depending on your environment and workload, it may take some time for the standby's node record to propagate from the master to the standby. Some actions (such as starting
repmgrd) require that the standby's node record is present and up-to-date to function correctly - by providing the option--wait-syncto therepmgr standby registercommand,repmgrwill wait until the record is synchronised before exiting. An optional timeout (in seconds) can be added to this option (e.g.--wait-sync=60).
Under some circumstances you may wish to register a standby which is not
yet running; this can be the case when using provisioning tools to create
a complex replication cluster. In this case, by using the -F/--force
option and providing the connection parameters to the master server,
the standby can be registered.
Similarly, with cascading replication it may be necessary to register
a standby whose upstream node has not yet been registered - in this case,
using -F/--force will result in the creation of an inactive placeholder
record for the upstream node, which will however later need to be registered
with the -F/--force option too.
When used with standby register, care should be taken that use of the
-F/--force option does not result in an incorrectly configured cluster.
repmgr standby clone also supports Barman, the Backup and
Replication manager (http://www.pgbarman.org/), as a provider of both
base backups and WAL files.
Barman support provides the following advantages:
- the master node does not need to perform a new backup every time a new standby is cloned;
- a standby node can be disconnected for longer periods without losing the ability to catch up, and without causing accumulation of WAL files on the master node;
- therefore,
repmgrdoes not need to use replication slots, and the master node does not need to setwal_keep_segments.
NOTE: In view of the above, Barman support is incompatible with the
use_replication_slotssetting inrepmgr.conf.
In order to enable Barman support for repmgr standby clone, you must
ensure that:
- the name of the server configured in Barman is equal to the
cluster_namesetting inrepmgr.conf; - the
barman_serversetting inrepmgr.confis set to the SSH hostname of the Barman server; - the
restore_commandsetting inrepmgr.confis configured to use a copy of thebarman-wal-restorescript shipped with thebarman-clipackage (see below); - the Barman catalogue includes at least one valid backup for this server.
NOTE: Barman support is automatically enabled if
barman_serveris set. Normally it is a good practice to use Barman, for instance when fetching a base backup while cloning a standby; in any case, Barman mode can be disabled using the--without-barmancommand line option.
NOTE: if you have a non-default SSH configuration on the Barman server, e.g. using a port other than 22, then you can set those parameters in a dedicated Host section in
~/.ssh/configcorresponding to the value ofbarman_serverinrepmgr.conf. See the "Host" section inman 5 ssh_configfor more details.
barman-wal-restore is a Python script provided by the Barman
development team as part of the barman-cli package (Barman 2.0
and later; for Barman 1.x the script is provided separately as
barman-wal-restore.py).
restore_command must then be set in repmgr.conf as follows:
<script> <Barman hostname> <cluster_name> %f %p
For instance, suppose that we have installed Barman on the barmansrv
host, and that barman-wal-restore is located as an executable at
/usr/bin/barman-wal-restore; repmgr.conf should include the following
lines:
barman_server=barmansrv
restore_command=/usr/bin/barman-wal-restore barmansrv test %f %p
NOTE: to use a non-default Barman configuration file on the Barman server,
specify this in repmgr.conf with barman_config:
barman_config=/path/to/barman.conf
Now we can clone a standby using the Barman server:
$ repmgr -h node1 -d repmgr -D 9.5/main -f /etc/repmgr.conf standby clone
NOTICE: destination directory '9.5/main' provided
NOTICE: getting backup from Barman...
NOTICE: standby clone (from Barman) complete
NOTICE: you can now start your PostgreSQL server
HINT: for example : pg_ctl -D 9.5/data start
HINT: After starting the server, you need to register this standby with "repmgr standby register"
The above section demonstrates the simplest possible way to clone a standby server. Depending on your circumstances, finer-grained control over the cloning process may be necessary.
By default, pg_basebackup performs a checkpoint before beginning the backup
process. However, a normal checkpoint may take some time to complete;
a fast checkpoint can be forced with the -c/--fast-checkpoint option.
However this may impact performance of the server being cloned from
so should be used with care.
Further options can be passed to the pg_basebackup utility via
the setting pg_basebackup_options in repmgr.conf. See the PostgreSQL
documentation for more details of available options:
https://www.postgresql.org/docs/current/static/app-pgbasebackup.html
By default repmgr uses the pg_basebackup utility to clone a standby's
data directory from the master. Under some circumstances it may be
desirable to use rsync to do this, such as when resyncing the data
directory of a failed server with an active replication node.
To use rsync instead of pg_basebackup, provide the -r/--rsync-only
option when executing repmgr standby clone.
Note that repmgr forces rsync to use --checksum mode to ensure that all
the required files are copied. This results in additional I/O on both source
and destination server as the contents of files existing on both servers need
to be compared, meaning this method is not necessarily faster than making a
fresh clone with pg_basebackup.
NOTE:
barman-wal-restoresupports command line switches to control parallelism (--parallel=N) and compression (--bzip2,--gzip).
The primary_conninfo setting in recovery.conf generated by repmgr
is generated from the following sources, in order of highest to lowest priority:
- the upstream node's
conninfosetting (as defined in therepl_nodestable) - the connection parameters provided to
repmgr standby clone - PostgreSQL's standard connection defaults, including any environment variables set on the local node.
To include specific connection parameters other than the standard host, port,
username and database values (e.g. sslmode), include these in a conninfo-style
string passed to repmgr with -d/--dbname (see above for details), and/or set
appropriate environment variables.
Note that PostgreSQL will always set explicit defaults for sslmode and
sslcompression (and from PostgreSQL 10.0 also target_session_attrs).
If application_name is set in the standby's conninfo parameter in
repmgr.conf, this value will be appended to primary_conninfo, otherwise
repmgr will set application_name to the same value as the node_name
parameter.
By default repmgr assumes the user who owns the repmgr metadatabase will
also be the replication user; a different replication user can be specified
with --replication-user.
If the upstream server requires a password, and this was provided via
PGPASSWORD, .pgpass etc., by default repmgr will include this in
primary_conninfo. Use the command line option --no-conninfo-password to
suppress this.
Cascading replication, introduced with PostgreSQL 9.2, enables a standby server to replicate from another standby server rather than directly from the master, meaning replication changes "cascade" down through a hierarchy of servers. This can be used to reduce load on the master and minimize bandwith usage between sites.
repmgr supports cascading replication. When cloning a standby, in repmgr.conf
set the parameter upstream_node to the id of the server the standby
should connect to, and repmgr will perform the clone using this server
and create recovery.conf to point to it. Note that if upstream_node
is not explicitly provided, repmgr will use the master as the server
to clone from.
To demonstrate cascading replication, ensure you have a master and standby
set up as shown above in the section "Setting up a simple replication cluster
with repmgr". Create an additional standby server with repmgr.conf looking
like this:
cluster=test
node=3
node_name=node3
conninfo='host=repmgr_node3 user=repmgr dbname=repmgr'
upstream_node=2
Ensure upstream_node contains the node id of the previously
created standby. Clone this standby (using the connection parameters
for the existing standby) and register it:
$ repmgr -h repmgr_node2 -U repmgr -d repmgr -D /path/to/node3/data/ -f /etc/repmgr.conf standby clone
NOTICE: destination directory 'node_3/data/' provided
NOTICE: starting backup (using pg_basebackup)...
HINT: this may take some time; consider using the -c/--fast-checkpoint option
NOTICE: standby clone (using pg_basebackup) complete
NOTICE: you can now start your PostgreSQL server
HINT: for example : pg_ctl -D /path/to/node_3/data start
$ repmgr -f /etc/repmgr.conf standby register
NOTICE: standby node correctly registered for cluster test with id 3 (conninfo: host=repmgr_node3 dbname=repmgr user=repmgr)
After starting the standby, the repl_nodes table will look like this:
repmgr=# SELECT * FROM repmgr_test.repl_nodes ORDER BY id;
id | type | upstream_node_id | cluster | name | conninfo | slot_name | priority | active
----+---------+------------------+---------+-------+---------------------------------------------+-----------+----------+--------
1 | master | | test | node1 | host=repmgr_node1 dbname=repmgr user=repmgr | | 100 | t
2 | standby | 1 | test | node2 | host=repmgr_node2 dbname=repmgr user=repmgr | | 100 | t
3 | standby | 2 | test | node3 | host=repmgr_node3 dbname=repmgr user=repmgr | | 100 | t
(3 rows)
TIP: under some circumstances when setting up a cascading replication cluster, you may wish to clone a downstream standby whose upstream node does not yet exist. In this case you can clone from the master (or another upstream node) and provide the parameter
--upstream-conninfoto explictly set the upstream'sprimary_conninfostring inrecovery.conf.
Replication slots were introduced with PostgreSQL 9.4 and are designed to ensure
that any standby connected to the master using a replication slot will always
be able to retrieve the required WAL files. This removes the need to manually
manage WAL file retention by estimating the number of WAL files that need to
be maintained on the master using wal_keep_segments. Do however be aware
that if a standby is disconnected, WAL will continue to accumulate on the master
until either the standby reconnects or the replication slot is dropped.
To enable repmgr to use replication slots, set the boolean parameter
use_replication_slots in repmgr.conf:
use_replication_slots=1
Note that repmgr will fail with an error if this option is specified when
working with PostgreSQL 9.3.
Replication slots must be enabled in postgresql.conf by setting the parameter
max_replication_slots to at least the number of expected standbys (changes
to this parameter require a server restart).
When cloning a standby, repmgr will automatically generate an appropriate
slot name, which is stored in the repl_nodes table, and create the slot
on the master:
repmgr=# SELECT * from repl_nodes ORDER BY id;
id | type | upstream_node_id | cluster | name | conninfo | slot_name | priority | active
----+---------+------------------+---------+-------+------------------------------------------+---------------+----------+--------
1 | master | | test | node1 | host=localhost dbname=repmgr user=repmgr | repmgr_slot_1 | 100 | t
2 | standby | 1 | test | node2 | host=localhost dbname=repmgr user=repmgr | repmgr_slot_2 | 100 | t
3 | standby | 1 | test | node3 | host=localhost dbname=repmgr user=repmgr | repmgr_slot_3 | 100 | t
repmgr=# SELECT * FROM pg_replication_slots ;
slot_name | plugin | slot_type | datoid | database | active | active_pid | xmin | catalog_xmin | restart_lsn
---------------+--------+-----------+--------+----------+--------+------------+------+--------------+-------------
repmgr_slot_3 | | physical | | | t | 26060 | | | 0/50028F0
repmgr_slot_2 | | physical | | | t | 26079 | | | 0/50028F0
(2 rows)
Note that a slot name will be created by default for the master but not
actually used unless the master is converted to a standby using e.g.
repmgr standby switchover.
Further information on replication slots in the PostgreSQL documentation: https://www.postgresql.org/docs/current/interactive/warm-standby.html#STREAMING-REPLICATION-SLOTS
If a master server fails or needs to be removed from the replication cluster,
a new master server must be designated, to ensure the cluster continues
working correctly. This can be done with repmgr standby promote, which promotes
the standby on the current server to master
To demonstrate this, set up a replication cluster with a master and two attached
standby servers so that the repl_nodes table looks like this:
repmgr=# SELECT * FROM repmgr_test.repl_nodes ORDER BY id;
id | type | upstream_node_id | cluster | name | conninfo | slot_name | priority | active
----+---------+------------------+---------+-------+---------------------------------------------+-----------+----------+--------
1 | master | | test | node1 | host=repmgr_node1 dbname=repmgr user=repmgr | | 100 | t
2 | standby | 1 | test | node2 | host=repmgr_node2 dbname=repmgr user=repmgr | | 100 | t
3 | standby | 1 | test | node3 | host=repmgr_node3 dbname=repmgr user=repmgr | | 100 | t
(3 rows)
Stop the current master with e.g.:
$ pg_ctl -D /path/to/node_1/data -m fast stop
At this point the replication cluster will be in a partially disabled state with
both standbys accepting read-only connections while attempting to connect to the
stopped master. Note that the repl_nodes table will not yet have been updated
and will still show the master as active.
Promote the first standby with:
$ repmgr -f /etc/repmgr.conf standby promote
This will produce output similar to the following:
ERROR: connection to database failed: could not connect to server: Connection refused
Is the server running on host "repmgr_node1" (192.161.2.1) and accepting
TCP/IP connections on port 5432?
could not connect to server: Connection refused
Is the server running on host "repmgr_node1" (192.161.2.1) and accepting
TCP/IP connections on port 5432?
NOTICE: promoting standby
NOTICE: promoting server using '/usr/bin/postgres/pg_ctl -D /path/to/node_2/data promote'
server promoting
NOTICE: STANDBY PROMOTE successful
Note: the first ERROR is repmgr attempting to connect to the current
master to verify that it has failed. If a valid master is found, repmgr
will refuse to promote a standby.
The repl_nodes table will now look like this:
id | type | upstream_node_id | cluster | name | conninfo | slot_name | priority | active
----+---------+------------------+---------+-------+---------------------------------------------+-----------+----------+--------
1 | master | | test | node1 | host=repmgr_node1 dbname=repmgr user=repmgr | | 100 | f
2 | master | | test | node2 | host=repmgr_node2 dbname=repmgr user=repmgr | | 100 | t
3 | standby | 1 | test | node3 | host=repmgr_node3 dbname=repmgr user=repmgr | | 100 | t
(3 rows)
The previous master has been marked as inactive, and node2's upstream_node_id
has been cleared as it's now the "topmost" server in the replication cluster.
However the sole remaining standby is still trying to replicate from the failed
master; repmgr standby follow must now be executed to rectify this situation.
Following the failure or removal of the replication cluster's existing master
server, repmgr standby follow can be used to make 'orphaned' standbys
follow the new master and catch up to its current state.
To demonstrate this, assuming a replication cluster in the same state as the end of the preceding section ("Promoting a standby server with repmgr"), execute this:
$ repmgr -f /etc/repmgr.conf -D /path/to/node_3/data/ -h repmgr_node2 -U repmgr -d repmgr standby follow
NOTICE: restarting server using '/usr/bin/postgres/pg_ctl -D /path/to/node_3/data/ -w -m fast restart'
waiting for server to shut down.... done
server stopped
waiting for server to start.... done
server started
The standby is now replicating from the new master and repl_nodes has been
updated to reflect this:
id | type | upstream_node_id | cluster | name | conninfo | slot_name | priority | active
----+---------+------------------+---------+-------+---------------------------------------------+-----------+----------+--------
1 | master | | test | node1 | host=repmgr_node1 dbname=repmgr user=repmgr | | 100 | f
2 | master | | test | node2 | host=repmgr_node2 dbname=repmgr user=repmgr | | 100 | t
3 | standby | 2 | test | node3 | host=repmgr_node3 dbname=repmgr user=repmgr | | 100 | t
(3 rows)
Note that with cascading replication, repmgr standby follow can also be
used to detach a standby from its current upstream server and follow the
master. However it's currently not possible to have it follow another standby;
we hope to improve this in a future release.
A typical use-case for replication is a combination of master and standby server, with the standby serving as a backup which can easily be activated in case of a problem with the master. Such an unplanned failover would normally be handled by promoting the standby, after which an appropriate action must be taken to restore the old master.
In some cases however it's desirable to promote the standby in a planned
way, e.g. so maintenance can be performed on the master; this kind of switchover
is supported by the repmgr standby switchover command.
repmgr standby switchover differs from other repmgr actions in that it
also performs actions on another server, for which reason you must provide
both passwordless SSH access and the path of repmgr.conf on that server.
NOTE
repmgr standby switchoverperforms a relatively complex series of operations on two servers, and should therefore be performed after careful preparation and with adequate attention. In particular you should be confident that your network environment is stable and reliable.We recommend running
repmgr standby switchoverat the most verbose logging level (--log-level DEBUG --verbose) and capturing all output to assist troubleshooting any problems.Please also read carefully the list of caveats below.
To demonstrate switchover, we will assume a replication cluster running on
PostgreSQL 9.5 or later with a master (node1) and a standby (node2);
after the switchover node2 should become the master with node1 following it.
The switchover command must be run from the standby which is to be promoted, and in its simplest form looks like this:
repmgr -f /etc/repmgr.conf -C /etc/repmgr.conf standby switchover
-f /etc/repmgr.conf is, as usual the local repmgr node's configuration file.
-C /etc/repmgr.conf is the path to the configuration file on the current
master, which is required to execute repmgr remotely on that server;
if it is not provided with -C, repmgr will check the same path as on the
local server, as well as the normal default locations. repmgr will check
this file can be found before performing any further actions.
$ repmgr -f /etc/repmgr.conf -C /etc/repmgr.conf standby switchover -v
NOTICE: using configuration file "/etc/repmgr.conf"
NOTICE: switching current node 2 to master server and demoting current master to standby...
NOTICE: 5 files copied to /tmp/repmgr-node1-archive
NOTICE: connection to database failed: FATAL: the database system is shutting down
NOTICE: current master has been stopped
ERROR: connection to database failed: FATAL: the database system is shutting down
NOTICE: promoting standby
NOTICE: promoting server using '/usr/local/bin/pg_ctl -D /var/lib/postgresql/9.5/node_2/data promote'
server promoting
NOTICE: STANDBY PROMOTE successful
NOTICE: Executing pg_rewind on old master server
NOTICE: 5 files copied to /var/lib/postgresql/9.5/data
NOTICE: restarting server using '/usr/local/bin/pg_ctl -w -D /var/lib/postgresql/9.5/node_1/data -m fast restart'
pg_ctl: PID file "/var/lib/postgresql/9.5/node_1/data/postmaster.pid" does not exist
Is server running?
starting server anyway
NOTICE: node 1 is replicating in state "streaming"
NOTICE: switchover was successful
Messages containing the line connection to database failed: FATAL: the database system is shutting down are not errors - repmgr is polling the old master database
to make sure it has shut down correctly. repmgr will also archive any
configuration files in the old master's data directory as they will otherwise
be overwritten by pg_rewind; they are restored once the pg_rewind operation
has completed.
The old master is now replicating as a standby from the new master and repl_nodes
should have been updated to reflect this:
repmgr=# SELECT * from repl_nodes ORDER BY id;
id | type | upstream_node_id | cluster | name | conninfo | slot_name | priority | active
----+---------+------------------+---------+-------+------------------------------------------+-----------+----------+--------
1 | standby | 2 | test | node1 | host=localhost dbname=repmgr user=repmgr | | 100 | t
2 | master | | test | node2 | host=localhost dbname=repmgr user=repmgr | | 100 | t
(2 rows)
- The functionality provided
repmgr standby switchoveris primarily aimed at a two-server master/standby replication cluster and currently does not support additional standbys. repmgr standby switchoveris designed to use thepg_rewindutility, standard in 9.5 and later and available separately in 9.3 and 9.4 (see note below)pg_rewindrequires that eitherwal_log_hintsis enabled, or that data checksums were enabled when the cluster was initialized. See thepg_rewinddocumentation for details: https://www.postgresql.org/docs/current/static/app-pgrewind.htmlrepmgrdshould not be running when a switchover is carried out, otherwise therepmgrdmay try and promote a standby by itself.- Any other standbys attached to the old master will need to be manually
instructed to point to the new master (e.g. with
repmgr standby follow). - You must ensure that following a server start using
pg_ctl, log output is not send to STDERR (the default behaviour). If logging is not configured, we recommend settinglogging_collector=oninpostgresql.confand providing an explicit-l/--logsetting inrepmgr.conf'spg_ctl_optionsparameter.
We hope to remove some of these restrictions in future versions of repmgr.
In order to efficiently reintegrate a demoted master into the replication cluster as a standby, it's necessary to resynchronise its data directory with that of the current master, as it's very likely that their timelines will have diverged slightly following the shutdown of the old master.
The utility pg_rewind provides an efficient way of doing this, however
is not included in the core PostgreSQL distribution for versions 9.3 and 9.4.
However, pg_rewind is available separately for these versions and we
strongly recommend its installation. To use it with versions 9.3 and 9.4,
provide the command line option --pg_rewind, optionally with the
path to the pg_rewind binary location if not installed in the PostgreSQL
bin directory.
pg_rewind for versions 9.3 and 9.4 can be obtained from:
https://github.com/vmware/pg_rewind
Note that building this version of pg_rewind requires the PostgreSQL source
code. Also, PostgreSQL 9.3 does not provide wal_log_hints, meaning data
checksums must have been enabled when the database was initialized.
If pg_rewind is not available, as a fallback repmgr will use repmgr standby clone to resynchronise the old master's data directory using
rsync. However, in order to ensure all files are synchronised, the
entire data directory on both servers must be scanned, a process which
can take some time on larger databases, in which case you should
consider making a fresh standby clone.
To unregister a running standby, execute:
repmgr standby unregister -f /etc/repmgr.conf
This will remove the standby record from repmgr's internal metadata
table (repl_nodes). A standby_unregister event notification will be
recorded in the repl_events table.
Note that this command will not stop the server itself or remove it from the replication cluster. Note that if the standby was using a replication slot, this will not be removed.
If the standby is not running, the command can be executed on another
node by providing the id of the node to be unregistered using
the command line parameter --node, e.g. executing the following
command on the master server will unregister the standby with
id 3:
repmgr standby unregister -f /etc/repmgr.conf --node=3
repmgrd is a management and monitoring daemon which runs on standby nodes
and which can automate actions such as failover and updating standbys to
follow the new master.
To use repmgrd for automatic failover, postgresql.conf must contain the
following line:
shared_preload_libraries = 'repmgr_funcs'
(changing this setting requires a restart of PostgreSQL).
Additionally the following repmgrd options must be set in repmgr.conf:
failover=automatic
promote_command='repmgr standby promote -f /etc/repmgr.conf --log-to-file'
follow_command='repmgr standby follow -f /etc/repmgr.conf --log-to-file'
Note that the --log-to-file option will cause repmgr's output to be logged to
the destination configured to receive log output for repmgrd.
See repmgr.conf.sample for further repmgrd-specific settings
When failover is set to automatic, upon detecting failure of the current
master, repmgrd will execute one of promote_command or follow_command,
depending on whether the current server is becoming the new master or
needs to follow another server which has become the new master. Note that
these commands can be any valid shell script which results in one of these
actions happening, but we strongly recommend executing repmgr directly.
repmgrd can be started simply with e.g.:
repmgrd -f /etc/repmgr.conf --verbose >> $HOME/repmgr/repmgr.log 2>&1
For permanent operation, we recommend using the options -d/--daemonize to
detach the repmgrd process, and -p/--pid-file to write the process PID
to a file.
Note that currently repmgrd is not required to run on the master server.
To demonstrate automatic failover, set up a 3-node replication cluster (one master
and two standbys streaming directly from the master) so that the repl_nodes
table looks like this:
repmgr=# SELECT * FROM repmgr_test.repl_nodes ORDER BY id;
id | type | upstream_node_id | cluster | name | conninfo | slot_name | priority | active
----+---------+------------------+---------+-------+---------------------------------------------+-----------+----------+--------
1 | master | | test | node1 | host=repmgr_node1 dbname=repmgr user=repmgr | | 100 | t
2 | standby | 1 | test | node2 | host=repmgr_node2 dbname=repmgr user=repmgr | | 100 | t
3 | standby | 1 | test | node3 | host=repmgr_node3 dbname=repmgr user=repmgr | | 100 | t
(3 rows)
Start repmgrd on each standby and verify that it's running by examining
the log output, which at log level INFO will look like this:
[2016-01-05 13:15:40] [INFO] checking cluster configuration with schema 'repmgr_test'
[2016-01-05 13:15:40] [INFO] checking node 2 in cluster 'test'
[2016-01-05 13:15:40] [INFO] reloading configuration file and updating repmgr tables
[2016-01-05 13:15:40] [INFO] starting continuous standby node monitoring
Each repmgrd should also have noted its successful startup in the repl_events
table:
repmgr=# SELECT * FROM repl_events WHERE event = 'repmgrd_start';
node_id | event | successful | event_timestamp | details
---------+---------------+------------+-------------------------------+---------
2 | repmgrd_start | t | 2016-01-27 18:22:38.080231+09 |
3 | repmgrd_start | t | 2016-01-27 18:22:38.08756+09 |
(2 rows)
Now stop the current master server with e.g.:
pg_ctl -D /path/to/node1/data -m immediate stop
This will force the master node to shut down straight away, aborting all
processes and transactions. This will cause a flurry of activity in
the repmgrd log files as each repmgrd detects the failure of the master
and a failover decision is made. Here extracts from the standby server
promoted to new master:
[2016-01-06 18:32:58] [WARNING] connection to upstream has been lost, trying to recover... 15 seconds before failover decision
[2016-01-06 18:33:03] [WARNING] connection to upstream has been lost, trying to recover... 10 seconds before failover decision
[2016-01-06 18:33:08] [WARNING] connection to upstream has been lost, trying to recover... 5 seconds before failover decision
...
[2016-01-06 18:33:18] [NOTICE] this node is the best candidate to be the new master, promoting...
...
[2016-01-06 18:33:20] [NOTICE] STANDBY PROMOTE successful
and here from the standby server which is now following the new master:
[2016-01-06 18:32:58] [WARNING] connection to upstream has been lost, trying to recover... 15 seconds before failover decision
[2016-01-06 18:33:03] [WARNING] connection to upstream has been lost, trying to recover... 10 seconds before failover decision
[2016-01-06 18:33:08] [WARNING] connection to upstream has been lost, trying to recover... 5 seconds before failover decision
...
[2016-01-06 18:33:23] [NOTICE] node 2 is the best candidate for new master, attempting to follow...
[2016-01-06 18:33:23] [INFO] changing standby's master
...
[2016-01-06 18:33:25] [NOTICE] node 3 now following new upstream node 2
The repl_nodes table should have been updated to reflect the new situation,
with the original master (node1) marked as inactive, and standby node3
now following the new master (node2):
repmgr=# SELECT * from repl_nodes ORDER BY id;
id | type | upstream_node_id | cluster | name | conninfo | slot_name | priority | active
----+---------+------------------+---------+-------+------------------------------------------+-----------+----------+--------
1 | master | | test | node1 | host=localhost dbname=repmgr user=repmgr | | 100 | f
2 | master | | test | node2 | host=localhost dbname=repmgr user=repmgr | | 100 | t
3 | standby | 2 | test | node3 | host=localhost dbname=repmgr user=repmgr | | 100 | t
(3 rows)
The repl_events table will contain a summary of what happened to each server
during the failover:
repmgr=# SELECT * from repmgr_test.repl_events where event_timestamp>='2016-01-06 18:30';
node_id | event | successful | event_timestamp | details
---------+--------------------------+------------+-------------------------------+----------------------------------------------------------
2 | standby_promote | t | 2016-01-06 18:33:20.061736+09 | node 2 was successfully promoted to master
2 | repmgrd_failover_promote | t | 2016-01-06 18:33:20.067132+09 | node 2 promoted to master; old master 1 marked as failed
3 | repmgrd_failover_follow | t | 2016-01-06 18:33:25.331012+09 | node 3 now following new upstream node 2
(3 rows)
Note that currently repmgrd does not provide logfile rotation. To ensure
the current logfile does not grow indefinitely, configure your system's logrotate
to do this. Sample configuration to rotate logfiles weekly with retention
for up to 52 weeks and rotation forced if a file grows beyond 100Mb:
/var/log/postgresql/repmgr-9.5.log {
missingok
compress
rotate 52
maxsize 100M
weekly
create 0600 postgres postgres
}
In addition to the repmgr configuration settings, parameters in the
conninfo string influence how repmgr makes a network connection to
PostgreSQL. In particular, if another server in the replication cluster
is unreachable at network level, system network settings will influence
the length of time it takes to determine that the connection is not possible.
In particular explicitly setting a parameter for connect_timeout should
be considered; the effective minimum value of 2 (seconds) will ensure
that a connection failure at network level is reported as soon as possible,
otherwise depending on the system settings (e.g. tcp_syn_retries in Linux)
a delay of a minute or more is possible.
For further details on conninfo network connection parameters, see:
https://www.postgresql.org/docs/current/static/libpq-connect.html#LIBPQ-PARAMKEYWORDS
When repmgrd is running with the option -m/--monitoring-history, it will
constantly write standby node status information to the repl_monitor table,
providing a near-real time overview of replication status on all nodes
in the cluster.
The view repl_status shows the most recent state for each node, e.g.:
repmgr=# SELECT * FROM repmgr_test.repl_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 repl_monitor
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.
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. 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, 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.
In a situation caused e.g. by a network interruption between two data centres, it's important to avoid a "split-brain" situation where both sides of the network assume they are the active segment and the side without an active master unilaterally promotes one of its standbys.
To prevent this situation happening, it's essential to ensure that one network segment has a "voting majority", so other segments will know they're in the minority and not attempt to promote a new master. Where an odd number of servers exists, this is not an issue. However, if each network has an even number of nodes, it's necessary to provide some way of ensuring a majority, which is where the witness server becomes useful.
This is not a fully-fledged standby node and is not integrated into
replication, but it effectively represents the "casting vote" when
deciding which network segment has a majority. A witness server can
be set up using repmgr witness create (see below for details) and
can run on a dedicated server or an existing node. Note that it only
makes sense to create a witness server in conjunction with running
repmgrd; the witness server will require its own repmgrd instance.
Cascading replication - where a standby can connect to an upstream node and not
the master server itself - was introduced in PostgreSQL 9.2. repmgr and
repmgrd support cascading replication by keeping track of the relationship
between standby servers - each node record is stored with the node id of its
upstream ("parent") server (except of course the master server).
In a failover situation where the master node fails and a top-level standby is promoted, a standby connected to another standby will not be affected and continue working as normal (even if the upstream standby it's connected to becomes the master node). If however the node's direct upstream fails, the "cascaded standby" will attempt to reconnect to that node's parent.
Each time repmgr or repmgrd perform a significant event, a record
of that event is written into the repl_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 master was registered and a standby cloned and registered:
repmgr=# SELECT * from repmgr_test.repl_events ;
node_id | event | successful | event_timestamp | details
---------+------------------+------------+-------------------------------+-------------------------------------------------------------------------------------
1 | master_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)
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"'
By default, all notifications will be passed; the notification types can be filtered to explicitly named ones:
event_notifications=master_register,standby_register,witness_create
The following event types are available:
master_registerstandby_registerstandby_unregisterstandby_clonestandby_promotestandby_followstandby_switchoverstandby_disconnect_manualwitness_createwitness_registerwitness_unregisterrepmgrd_startrepmgrd_shutdownrepmgrd_failover_promoterepmgrd_failover_follow
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 repl_events
table, in which case event_notification_command can serve as a fallback.
repmgr is updated regularly with point releases (e.g. 3.0.2 to 3.0.3)
containing bugfixes and other minor improvements. Any substantial new
functionality will be included in a feature release (e.g. 3.0.x to 3.1.x).
In general repmgr can be upgraded as-is without any further action required,
however feature releases may require the repmgr database to be upgraded.
An SQL script will be provided - please check the release notes for details:
repmgr is largely OS-agnostic and can be run on any UNIX-like environment
including various Linux distributions, Solaris, macOS and the various BSDs.
However, often OS-specific configuration is required, particularly when dealing with system service management (e.g. stopping and starting the PostgreSQL server), file paths and configuration file locations.
By default, repmgr will use PostgreSQL's standard pg_ctl utility to control
a running PostgreSQL server. However it may be better to use the operating
system's service management system, e.g. systemd. To specify which service
control commands are used, the following repmgr.conf configuration settings
are available:
service_start_command
service_stop_command
service_restart_command
service_reload_command
service_promote_command
See repmgr.conf.sample for further details.
Some PostgreSQL system packages, such as those provided for Debian/Ubuntu, like
to hide some PostgreSQL utility programs outside of the default path. To ensure
repmgr finds all required executables, explicitly set pg_bindir to the
appropriate location, e.g. for PostgreSQL 9.6 on Debian/Ubuntu this would be
/usr/lib/postgresql/9.6/bin/.
For some command line and most configuration file parameters, repmgr falls
back to default values if values for these are not explicitly provided.
The file repmgr.conf.sample documents the default value of configuration
parameters if one is set. Of particular note is the log level, which
defaults to NOTICE; particularly when using repmgr from the command line
it may be useful to set this to a higher level with -L/--log-level. e.g.
to INFO.
Execute repmgr --help to see the default values for various command
line parameters, particularly database connection parameters.
See the section Configuration above for information on how the
configuration file is located if -f/--config-file is not supplied.
The repmgr command line tool accepts commands for specific servers in the
replication in the format "server_type action", or for the entire
replication cluster in the format "cluster action". Each command is
described below.
In general, each command needs to be provided with the path to repmgr.conf,
which contains connection details for the local database.
-
master registerRegisters a master in a cluster. This command needs to be executed before any standby nodes are registered.
primary registercan be used as an alias formaster register. -
standby registerRegisters a standby with
repmgr. This command needs to be executed to enable promote/follow operations and to allowrepmgrdto work with the node. An existing standby can be registered using this command. -
standby unregisterUnregisters a standby with
repmgr. This command does not affect the actual replication, just removes the standby's entry from therepl_nodestable. -
standby clone [node to be cloned]Clones a new standby node from the data directory of the master (or an upstream cascading standby) using
pg_basebackuporrsync. Additionally it will create therecovery.conffile required to start the server as a standby. This command does not requirerepmgr.confto be provided, but does require connection details of the master or upstream server as command line parameters.Provide the
-D/--data-diroption to specify the destination data directory; if not, the same directory path as on the source server will be used. By default,pg_basebackupwill be used to copy data from the master or upstream node but this can only be used for bootstrapping new installations. To update an existing but 'stale' data directory (for example belonging to a failed master),rsyncmust be used by specifying--rsync-only. In this case, passwordless SSH connections between servers are required. -
standby promotePromotes a standby to a master if the current master has failed. This command requires a valid
repmgr.conffile for the standby, either specified explicitly with-f/--config-fileor located in the current working directory; no additional arguments are required.If the standby promotion succeeds, the server will not need to be restarted. However any other standbys will need to follow the new server, by using
standby follow(see below); ifrepmgrdis active, it will handle this.This command will fail with an error if the current master is still running.
-
standby switchoverPromotes a standby to master and demotes the existing master to a standby. This command must be run on the standby to be promoted, and requires a passwordless SSH connection to the current master. Additionally the location of the master's
repmgr.conffile must be provided with-C/--remote-config-file.repmgrdshould not be active if a switchover is attempted. This restriction may be lifted in a later version. -
standby followAttaches the standby to a new master. This command requires a valid
repmgr.conffile for the standby, either specified explicitly with-f/--config-fileor located in the current working directory; no additional arguments are required.This command will force a restart of the standby server. It can only be used to attach a standby to a new master node.
-
witness createCreates a witness server as a separate PostgreSQL instance. This instance can be on a separate server or a server running an existing node. The witness server contain a copy of the repmgr metadata tables but will not be set up as a standby; instead it will update its metadata copy each time a failover occurs.
Note that it only makes sense to create a witness server if
repmgrdis in use; see section "Using a witness server" above.This command requires a
repmgr.conffile containing a valid conninfo string for the server to be created, as well as the other minimum required parameters detailed in the sectionrepmgr configuration fileabove.By default the witness server will use port 5499 to facilitate easier setup on a server running an existing node. To use a different port, supply this explicitly in the
repmgr.confconninfo string.This command also requires the location of the witness server's data directory to be provided (
-D/--datadir) as well as valid connection parameters for the master server. If not explicitly provided, database and user names will be extracted from theconninfostring inrepmgr.conf.By default this command will create a superuser and a repmgr user. The
repmgruser name will be extracted from theconninfostring inrepmgr.conf. -
witness registerThis will set up the witness server configuration, including the witness server's copy of the
repmgrmeta database, on a running PostgreSQL instance and register the witness server with the master. It requires the same command line options aswitness create. -
witness unregisterRemoves the entry for a witness server from the
repl_nodestable. This command will not shut down the witness server or remove its data directory. -
cluster showDisplays information about each active node in the replication cluster. This command polls each registered server and shows its role (
master/standby/witness) orFAILEDif the node doesn't respond. 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 a valid
repmgr.conffile to be provided; no additional arguments are needed.Example:
$ repmgr -f /etc/repmgr.conf cluster show Role | Name | Upstream | Connection String ----------+-------|----------|---------------------------------------- * master | node1 | | host=db_node1 dbname=repmgr user=repmgr standby | node2 | node1 | host=db_node2 dbname=repmgr user=repmgr standby | node3 | node2 | host=db_node3 dbname=repmgr user=repmgrTo show database connection errors when polling nodes, run the command in
--verbosemode.The
cluster showcommand now accepts the 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 2,0 3,1The first column is the node's ID, and the second column represents the node's status (0 = available, -1 = failed).
-
cluster matrixandcluster crosscheckThese commands display connection information for each pair of nodes in the replication cluster.
-
cluster matrixruns acluster showon each node and arranges the results in a matrix, recording success or failure; -
cluster crosscheckruns acluster matrixon 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.conffile on each node. Additionally passwordlesssshconnections 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 matrixis sufficient to establish the state of each possible connection.Example 2 (node1 and
node2up,node3down):$ 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
node3is 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 crosscheckgives the same result ascluster matrix, because from any functioning node we can observe the same state:node1andnode2are up,node3is down.Example 3 (all nodes up, firewall dropping packets originating from
node1and directed to port 5432 on node3)Running
cluster matrixfromnode1gives 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_timeoutsetting in the registered nodeconninfostrings; default is 1 minute which means without modification the above command would take around 2 minutes to run; see comment elsewhere about settingconnect_timeout)The matrix tells us that we cannot connect from
node1tonode3, and that (therefore) we don't know the state of any outbound connection from node3.In this case, the
cluster crosscheckcommand 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 crosscheckmerged its owncluster matrixwith thecluster matrixoutput fromnode2; the latter is able to connect tonode3and therefore determine the state of outbound connections from that node. -
-
cluster cleanupPurges monitoring history from the
repl_monitortable to prevent excessive table growth. Use the-k/--keep-historyto specify the number of days of monitoring history to retain. This command can be used manually or as a cronjob.This command requires a valid
repmgr.conffile for the node on which it is executed, either specified explicitly with-f/--config-fileor located in the current working directory; no additional arguments are required.
As well as this README, the repmgr source contains following additional
documentation files:
- FAQ.md - frequently asked questions
- CONTRIBUTING.md - how to contribute to
repmgr - PACKAGES.md - details on building packages
- SSH-RSYNC.md - how to set up passwordless SSH between nodes
- docs/repmgrd-failover-mechanism.md - how repmgrd picks which node to promote
- docs/repmgrd-node-fencing.md - how to "fence" a failed master node
repmgr or repmgrd will return one of the following error codes on program
exit:
- SUCCESS (0) Program ran successfully.
- ERR_BAD_CONFIG (1) Configuration file could not be parsed or was invalid
- ERR_BAD_RSYNC (2) An rsync call made by the program returned an error (repmgr only)
- ERR_NO_RESTART (4) An attempt to restart a PostgreSQL instance failed
- ERR_DB_CON (6) Error when trying to connect to a database
- ERR_DB_QUERY (7) Error while executing a database query
- ERR_PROMOTED (8) Exiting program because the node has been promoted to master
- ERR_STR_OVERFLOW (10) String overflow error
- ERR_FAILOVER_FAIL (11) Error encountered during failover (repmgrd only)
- ERR_BAD_SSH (12) Error when connecting to remote host via SSH (repmgr only)
- ERR_SYS_FAILURE (13) Error when forking (repmgrd only)
- ERR_BAD_BASEBACKUP (14) Error when executing pg_basebackup (repmgr only)
- ERR_MONITORING_FAIL (16) Unrecoverable error encountered during monitoring (repmgrd only)
- ERR_BAD_BACKUP_LABEL (17) Corrupt or unreadable backup label encountered (repmgr only)
- ERR_SWITCHOVER_FAIL (18) Error encountered during switchover (repmgr only)
- ERR_BARMAN (19) Unrecoverable error while accessing the barman server (repmgr only)
- ERR_REGISTRATION_SYNC (20) After registering a standby, local node record was not syncrhonised (repmgr only, with --wait option)
2ndQuadrant provides 24x7 production support for repmgr, including
configuration assistance, installation verification and training for
running a robust replication cluster. For further details see:
There is a mailing list/forum to discuss contributions or issues:
The IRC channel #repmgr is registered with freenode.
Please report bugs and other issues to:
Further information is available at http://www.repmgr.org/
We'd love to hear from you about how you use repmgr. Case studies and news are always welcome. Send us an email at [email protected], or send a postcard to
repmgr
c/o 2ndQuadrant
7200 The Quorum
Oxford Business Park North
Oxford
OX4 2JZ
United Kingdom
Thanks from the repmgr core team.
- Ian Barwick
- Jaime Casanova
- Abhijit Menon-Sen
- Simon Riggs
- Cedric Villemain