PostgreSQL 9+ allow us to have replicated Hot Standby servers which we can query and/or use for high availability.
While the main components of the feature are included with PostgreSQL, the user is expected to manage the high availability part of it.
repmgr allows you to monitor and manage your replicated PostgreSQL databases as a single cluster. repmgr includes two components:
- repmgr: command program that performs tasks and then exits
- repmgrd: management and monitoring daemon that watches the cluster and can automate remote actions.
repmgr works with PostgreSQL versions 9.0 and 9.1.
There are currently no incompatibilities when upgrading repmgr from 9.0 to 9.1, so your 9.0 configuration will work with 9.1
Additional parameters must be added to postgresql.conf to take advantage of the new 9.1 features such as synchronous replication or hot standby feedback.
repmgr is currently aimed for installation on UNIX-like systems that include
development tools such as gcc and gmake. It also requires that the
rsync utility is available in the PATH of the user running the repmgr
programs. Some operations also require PostgreSQL components such
as pg_config and pg_ctl be in the PATH.
Suppose we have 3 nodes: node1 (the initial master), node2 and node3. To make node2 and node3 be standbys of node1, execute this on both nodes (node2 and node3):
repmgr -D /var/lib/pgsql/9.0 standby clone node1
In order to get full monitoring and easier state transitions,
you register each of the nodes, by creating a repmgr.conf file
and executing commands like this on the appropriate nodes:
repmgr -f /var/lib/pgsql/repmgr/repmgr.conf --verbose master register repmgr -f /var/lib/pgsql/repmgr/repmgr.conf --verbose standby register
Once everything is registered, you start the repmgrd daemon. It will maintain a view showing the state of all the nodes in the cluster, including how far they are lagging behind the master.
If you lose node1 you can then run this on node2:
repmgr -f /var/lib/pgsql/repmgr/repmgr.conf standby promote
To make node2 the new master. Then on node3 run:
repmgr -f /var/lib/pgsql/repmgr/repmgr.conf standby follow
To make node3 follow node2 (rather than node1).
If now we want to add a new node, we can a prepare a new server (node4) and run:
repmgr -D /var/lib/pgsql/9.0 standby clone node2
And if a previously failed node becomes available again, such as the lost node1 above, you can get it to resynchronize by only copying over changes made while it was down using. That hapens with what's called a forced clone, which overwrites existing data rather than assuming it starts with an empty database directory tree:
repmgr -D /var/lib/pgsql/9.0 --force standby clone node1
This can be much faster than creating a brand new node that must copy over every file in the database.
To install and use repmgr and repmgrd follow these steps:
- Build repmgr programs
- Set up trusted copy between postgres accounts, needed for the
STANDBY CLONEstep - Check your primary server is correctly configured
- Write a suitable
repmgr.conffor the node - Setup repmgrd to aid in failover transitions
Both methods of installation will place the binaries at the same location as your
postgres binaries, such as psql. There are two ways to build it. The second
requires a full PostgreSQL source code tree to install the program directly into.
The first instead uses the PostgreSQL Extension System (PGXS) to install. For
this method to work, you will need the pg_config program available in your PATH.
In some distributions of PostgreSQL, this requires installing a separate
development package in addition to the basic server software.
If you are using a packaged PostgreSQL build and have pg_config
available, the package can be built and installed using PGXS instead:
tar xvzf repmgr-1.0.tar.gz cd repmgr make USE_PGXS=1 make USE_PGXS=1 install
This is preferred to building from the contrib subdirectory of the main
source code tree.
If you need to remove the source code temporary files from this directory, that can be done like this:
make USE_PGXS=1 clean
See below for building notes specific to RedHat Linux variants.
In this method, the repmgr distribution is copied into the PostgreSQL source
code tree, assumed to be at the ${postgresql_sources} for this example.
The resulting subdirectory must be named contrib/repmgr, without any
version number:
cp repmgr.tar.gz ${postgresql_sources}/contrib
cd ${postgresql_sources}/contrib
tar xvzf repmgr-1.0.tar.gz
cd repmgr
make
make install
If you need to remove the source code temporary files from this directory, that can be done like this:
make clean
The RPM packages of PostgreSQL put pg_config into the postgresql-devel
package, not the main server one. And if you have a RPM install of PostgreSQL
9.0, the entire PostgreSQL binary directory will not be in your PATH by default
either. Individual utilities are made available via the alternatives
mechanism, but not all commands will be wrapped that way. The files installed
by repmgr will certainly not be in the default PATH for the postgres user
on such a system. They will instead be in /usr/pgsql-9.0/bin/ on this
type of system.
When building repmgr against a RPM packaged build, you may discover that some development packages are needed as well. The following build errors can occur:
/usr/bin/ld: cannot find -lxslt /usr/bin/ld: cannot find -lpam
Install the following packages to correct those:
yum install libxslt-devel yum install pam-devel
If building repmgr as a regular user, then doing the install into the system
directories using sudo, the syntax is hard. pg_config won't be in root's
path either. The following recipe should work:
sudo PATH="/usr/pgsql-9.0/bin:$PATH" make USE_PGXS=1 install
If when building, you receive a series of errors of this form:
/usr/bin/ld: skipping incompatible /usr/pgsql-9.0/lib/libpq.so when searching for -lpq
This is likely because you have both the 32 and 64 bit versions of the
postgresql90-devel package installed. You can check that like this:
rpm -qa --queryformat '%{NAME}\t%{ARCH}\n' | grep postgresql90-devel
And if two packages appear, one for i386 and one for x86_64, that's not supposed to be allowed.
This can happen when using the PGDG repo to install that package; here is an example sessions demonstrating the problem case appearing:
# yum install postgresql-devel .. Setting up Install Process Resolving Dependencies --> Running transaction check ---> Package postgresql90-devel.i386 0:9.0.2-2PGDG.rhel5 set to be updated ---> Package postgresql90-devel.x86_64 0:9.0.2-2PGDG.rhel5 set to be updated --> Finished Dependency Resolution Dependencies Resolved ========================================================================= Package Arch Version Repository Size ========================================================================= Installing: postgresql90-devel i386 9.0.2-2PGDG.rhel5 pgdg90 1.5 M postgresql90-devel x86_64 9.0.2-2PGDG.rhel5 pgdg90 1.6 M
Note how both the i386 and x86_64 platform architectures are selected for installation. Your main PostgreSQL package will only be compatible with one of those, and if the repmgr build finds the wrong postgresql90-devel these "skipping incompatible" messages appear.
In this case, you can temporarily remove both packages, then just install the correct one for your architecture. Example:
rpm -e postgresql90-devel --allmatches yum install postgresql90-devel-9.0.2-2PGDG.rhel5.x86_64
Instead just deleting the package from the wrong platform might not leave behind the correct files, due to the way in which these accidentally happen to interact. If you already tried to build repmgr before doing this, you'll need to do:
make USE_PGXS=1 clean
To get rid of leftover files from the wrong architecture.
The Debian packages of PostgreSQL put pg_config into the development package
called postgresql-server-dev-$version.
When building repmgr against a Debian packages build, you may discover that some development packages are needed as well. You will need the following development packages installed:
sudo apt-get install libxslt-dev libxml2-dev libpam-dev libedit-dev
If your using Debian packages for PostgreSQL and are building repmgr with the USE_PGXS option you also need to install the corresponding development package:
sudo apt-get install postgresql-server-dev-9.0
If you build and install repmgr manually it will not be on the system path. The binaries will be installed in /usr/lib/postgresql/$version/bin/ which is not on the default path. The reason behind this is that Ubuntu/Debian systems manage multiple installed versions of PostgreSQL on the same system through a wrapper called pg_wrapper and repmgr is not (yet) known to this wrapper.
You can solve this in many different ways, the most Debian like is to make an alternate for repmgr and repmgrd:
sudo update-alternatives --install /usr/bin/repmgr repmgr /usr/lib/postgresql/9.0/bin/repmgr 10 sudo update-alternatives --install /usr/bin/repmgrd repmgrd /usr/lib/postgresql/9.0/bin/repmgrd 10
You can also make a deb package of repmgr using:
make USE_PGXS=1 deb
This will build a Debian package one level up from where you build, normally the same directory that you have your repmgr/ directory in.
You should now find the repmgr programs available in the subdirectory where the rest of your PostgreSQL installation is at. You can confirm the software is available by checking its version:
repmgr --version repmgrd --version
You may need to include the full path of the binary instead, such as this RHEL example:
/usr/pgsql-9.0/bin/repmgr --version /usr/pgsql-9.0/bin/repmgrd --version
Or in this Debian example:
/usr/lib/postgresql/9.0/bin/repmgr --version /usr/lib/postgresql/9.0/bin/repmgrd --version
Below this binary installation base directory is referred to as PGDIR.
Initial copy between nodes uses the rsync program running over ssh. For this to work, the postgres accounts on each system need to be able to access files on their partner node without a password.
First generate a ssh key, using an empty passphrase, and copy the resulting keys and a maching authorization file to a privledged user on the other system:
[postgres@node1]$ ssh-keygen -t rsa Generating public/private rsa key pair. Enter file in which to save the key (/var/lib/pgsql/.ssh/id_rsa): Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /var/lib/pgsql/.ssh/id_rsa. Your public key has been saved in /var/lib/pgsql/.ssh/id_rsa.pub. The key fingerprint is: aa:bb:cc:dd:ee:ff:aa:11:22:33:44:55:66:77:88:99 postgres@db1.domain.com [postgres@node1]$ cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys [postgres@node1]$ chmod go-rwx ~/.ssh/* [postgres@node1]$ cd ~/.ssh [postgres@node1]$ scp id_rsa.pub id_rsa authorized_keys postgres@node2:
Login as a user on the other system, and install the files into the postgres user's account:
[user@node2 ~]$ sudo chown postgres.postgres authorized_keys id_rsa.pub id_rsa [user@node2 ~]$ sudo mkdir -p ~postgres/.ssh [user@node2 ~]$ sudo chown postgres.postgres ~postgres/.ssh [user@node2 ~]$ sudo mv authorized_keys id_rsa.pub id_rsa ~postgres/.ssh [user@node2 ~]$ sudo chmod -R go-rwx ~postgres/.ssh
Now test that ssh in both directions works. You may have to accept some new known hosts in the process.
PostgreSQL should have been previously built and installed on the system. Here
is a sample of changes to the postgresql.conf file:
listen_addresses='*'
wal_level = 'hot_standby'
archive_mode = on
archive_command = 'cd .' # we can also use exit 0, anything that
# just does nothing
max_wal_senders = 10
wal_keep_segments = 5000 # 80 GB required on pg_xlog
hot_standby = on
Also you need to add the machines that will participate in the cluster in
pg_hba.conf file. One possibility is to trust all connections from the
replication users from all internal addresses, such as:
host all all 192.168.1.0/24 trust host replication all 192.168.1.0/24 trust
A more secure setup adds a repmgr user and database, just giving access to that user:
host repmgr repmgr 192.168.1.0/24 trust host replication all 192.168.1.0/24 trust
If you give a password to the user, you need to create a .pgpass file for
them as well to allow automatic login. In this case you might use the
md5 authentication method instead of trust for the repmgr user.
Don't forget to restart the database server after making all these changes.
This assumes you've already followed the steps in "Installation Outline" to install repmgr and repmgrd on the system.
A normal production installation of repmgr will normally involve two
different systems running on the same port, typically the default of 5432,
with both using files owned by the postgres user account. This
walkthrough assumes the following setup:
- A primary (master) server called "node1," running as the "postgres" user who is also the owner of the files. This server is operating on port 5432. This server will be known as "node1" in the cluster "test".
- A secondary (standby) server called "node2," running as the "postgres" user who is also the owner of the files. This server is operating on port 5432. This server will be known as "node2" in the cluster "test".
- Another standby server called "node3" with a similar configuration to "node2".
- The Postgress installation in each of the above is defined as $PGDATA,
which is represented here as
/var/lib/pgsql/9.0/data
If you already have a database with useful data to replicate, you can skip this step and use it instead. But if you do not already have data in this cluster to replication, you can create some like this:
createdb pgbench pgbench -i -s 10 pgbench
Examples below will use the database name pgbench to match this.
Substitute the name of your database instead. Note that the standby
nodes created here will include information for every database in the
cluster, not just the specified one. Needing the database name is
mainly for user authentication purposes.
Make sure that the "standby" user has a role in the database, "pgbench" in this case, and can login. On "node1":
createuser --login --superuser repmgr
Alternately you could start psql on the pgbench database on "node1" and at
the node1b# prompt type:
CREATE ROLE repmgr SUPERUSER LOGIN;
The main advantage of the latter is that you can do it remotely to any system you already have superuser access to.
To setup a new streaming replica, startin by removing any PostgreSQL installation on the existing standby nodes.
Stop any server on "node2" and "node3". You can confirm the database servers running using a command like this:
ps -eaf | grep postgres
And looking for the various database server processes: server, logger, wal writer, and autovacuum launcher.
Go to "node2" and "node3" database directories and remove the PostgreSQL installation:
cd $PGDATA rm -rf *
This will delete the entire database installation in
/var/lib/pgsql/9.0/data. Be careful that $PGDATA is defined here; executinglsto confirm you're in the right place is always a good idea before executingrm.
On the "node2" server, first test that you can connect to "node1" the way repmgr will by executing:
psql -h node1 -U repmgr -d pgbench
Possible sources for a problem here include:
Login role specified was not created on "node1"
The database configuration on "node1" is not listening on a TCP/IP port. That could be because the
listen_addressesparameter was not updated, or if it was but the server wasn't restarted afterwards. You can test this on "node1" itself the same way:psql -h node1 -U repmgr -d pgbench
With the "-h" parameter forcing a connnection over TCP/IP, rather than the default UNIX socket method.
There is a firewall setup that prevents incoming access to the PostgreSQL port (defaulting to 5432) used to access "node1". In this situation you would be able to connect to the "node1" server on itself, but not from any other host, and you'd just get a timeout when trying rather than a proper error message.
The
pg_hba.conffile does not list appropriate statements to allow this user to login. In this case you should connect to the server, but see an error message mentioning thepg_hba.conf.
With "node1" server running, we want to use the clone standby command
in repmgr to copy over the entire PostgreSQL database cluster onto the
"node2" server. Execute the clone process with:
repmgr -D $PGDATA -d pgbench -p 5432 -U repmgr -R postgres --verbose standby clone node1
Here "-U" specifies the database user to connect to the master as, while "-R" specifies what user to run the rsync command as. Potentially you could leave out one or both of these, in situations where the user and/or role setup is the same on each node.
If this fails with an error message about accessing the master database,
you should return to the previous step and confirm access to "node1"
from "node2" with psql, using the same parameters given to repmgr.
NOTE: you need to have $PGDIR/bin (where the PostgreSQL binaries are installed) in your path for the above to work. If you don't want that as a permanent setting, you can temporarily set it before running individual commands like this:
PATH=$PGDIR/bin:$PATH repmgr -D $PGDATA ...
Create a directory to store each repmgr configuration in for each node.
In that, there needs to be a repmgr.conf file for each node in the cluster.
For each node we'll assume this is stored in /var/lib/pgsql/repmgr/repmgr.conf
following the standard directory structure of a RHEL system. It should contain:
cluster=test node=1 conninfo='host=node1 user=repmgr dbname=pgbench'
On "node2" create the file /var/lib/pgsql/repmgr/repmgr.conf with:
cluster=test node=2 conninfo='host=node2 user=repmgr dbname=pgbench'
The STANDBY CLONE process should have created a recovery.conf file on "node2" in the $PGDATA directory that reads as follows:
standby_mode = 'on' primary_conninfo = 'host=node1 port=5432'
First, register the master by typing on "node1":
repmgr -f /var/lib/pgsql/repmgr/repmgr.conf --verbose master register
Then start the "standby" server.
You could now register the standby by typing on "node2":
repmgr -f /var/lib/pgsql/repmgr/repmgr.conf --verbose standby register
However, you can instead start repmgrd:
repmgrd -f /var/lib/pgsql/repmgr/repmgr.conf --verbose > /var/lib/pgsql/repmgr/repmgr.log 2>&1
Which will automatically register your standby system. And eventually you need repmgrd running anyway, to save lag monitoring information. repmgrd will log the deamon activity to the listed file. You can watch what it is doing with:
tail -f /var/lib/pgsql/repmgr/repmgr.log
Hit control-C to exit this tail command when you are done.
At this point, you have a functioning primary on "node1" and a functioning
standby server running on "node2". You can confirm the master knows
about the standby, and that it is keeping it current, by looking at
repl_status:
postgres@node2 $ psql -x -d pgbench -c "SELECT * FROM repmgr_test.repl_status" -[ RECORD 1 ]-------------+------------------------------ primary_node | 1 standby_node | 2 last_monitor_time | 2011-02-23 08:19:39.791974-05 last_wal_primary_location | 0/1902D5E0 last_wal_standby_location | 0/1902D5E0 replication_lag | 0 bytes apply_lag | 0 bytes time_lag | 00:26:13.30293
Some tests you might do at this point include:
- Insert some records into the primary server here, confirm they appear very quickly (within milliseconds) on the standby, and that the repl_status view advances accordingly.
- Verify that you can run queries against the standby server, but cannot make insertions into the standby database.
To simulate the loss of the primary server, simply stop the "node1" server.
At this point, the standby contains the database as it existed at the time of
the "failure" of the primary server. If looking at repl_status on
"node2", you should see the time_lag value increase the longer "node1"
is down.
Now you can promote the standby server to be the primary, to allow applications to read and write to the database again, by typing:
repmgr -f /var/lib/pgsql/repmgr/repmgr.conf --verbose standby promote
The server restarts and now has read/write ability.
To make the former primary act as a standby, which is necessary before restoring the original roles, type the following on node1:
repmgr -D $PGDATA -d pgbench -p 5432 -U repmgr -R postgres --verbose --force standby clone node2
Then start the "node1" server, which is now acting as a standby server. Check
Make sure the record(s) inserted the earlier step are still available on the now standby (prime). Confirm the database on "node1" is read-only.
Now restore to the original configuration by stopping
"node2" (now acting as a primary), promoting "node1" again to be the
primary server, then bringing up "node2" as a standby with a valid
recovery.conf file.
Stop the "node2" server:
repmgr -f /var/lib/pgsql/repmgr/repmgr.conf standby promote
Now the original primary, "node1" is acting again as primary.
Start the "node2" server and type this on "node1":
repmgr standby clone --force -h node2 -p 5432 -U postgres -R postgres --verbose
Verify the roles have reversed by attempting to insert a record on "node" and on "node1".
The servers are now again acting as primary on "node1" and standby on "node2".
Another test setup assumes you might be using the default installation of
PostgreSQL on port 5432 for some other purpose, and instead relocates these
instances onto different ports running as different users. In places where
127.0.0.1 is used as a host name, a more traditional configuration
would instead use the name of the relevant host for that parameter.
You can usually leave out changes to the port number in this case too.
- A primary (master) server called "prime," with a user as "prime," who is also the owner of the files. This server is operating on port 5433. This server will be known as "node1" in the cluster "test"
- A standby server called "standby", with a user of "standby", who is the owner of the files. This server is operating on port 5434. This server will be known and "node2" on the cluster "test."
- A database exists on "prime" called "testdb."
- The Postgress installation in each of the above is defined as $PGDATA,
which is represented here with
/data/primeas the "prime" server and/data/standbyas the "standby" server.
You might setup such an installation by adjusting the login script for the "prime" and "standby" users as in these two examples:
# prime PGDATA=/data/prime PGENGINE=/usr/pgsql-9.0/bin PGPORT=5433 export PGDATA PGENGINE PGPORT PATH="$PATH:$PGENGINE" # standby PGDATA=/data/standby PGENGINE=/usr/pgsql-9.0/bin PGPORT=5434 export PGDATA PGENGINE PGPORT PATH="$PATH:$PGENGINE"
And then starting/stopping each installation as needed using the pg_ctl
utility.
Note: naming your nodes based on their starting role is not a recommended best practice! As you'll see in this example, once there is a failover, names strongly associated with one particular role (primary or standby) can become confusing, once that node no longer has that role. Future versions of this walkthrough are expected to use more generic terminology for these names.
Setup a streaming replica, strip away any PostgreSQL installation on the existing replica:
Stop both servers.
Go to "standby" database directory and remove the PostgreSQL installation:
cd $PGDATA rm -rf *
This will delete the entire database installation in
/data/standby.
Create a directory to store each repmgr configuration in for each node.
In that, there needs to be a repmgr.conf file for each node in the cluster.
For "prime" we'll assume this is stored in /home/prime/repmgr
and it should contain:
cluster=test node=1 conninfo='host=127.0.0.1 dbname=testdb'
On "standby" create the file /home/standby/repmgr/repmgr.conf with:
cluster=test node=2 conninfo='host=127.0.0.1 dbname=testdb'
Next, with "prime" server running, we want to use the clone standby command
in repmgr to copy over the entire PostgreSQL database cluster onto the
"standby" server. On the "standby" server, type:
repmgr -D $PGDATA -p 5433 -U prime -R prime --verbose standby clone localhost
Next, we need a recovery.conf file on "standby" in the $PGDATA directory that reads as follows:
standby_mode = 'on' primary_conninfo = 'host=127.0.0.1 port=5433'
Make sure that standby has a qualifying role in the database, "testdb" in this
case, and can login. Start psql on the testdb database on "prime" and at
the testdb# prompt type:
CREATE ROLE standby SUPERUSER LOGIN
First, register the master by typing on "prime":
repmgr -f /home/prime/repmgr/repmgr.conf --verbose master register
On "standby," edit the postgresql.conf file and change the port to 5434.
Start the "standby" server.
Register the standby by typing on "standby":
repmgr -f /home/standby/repmgr/repmgr.conf --verbose standby register
At this point, you have a functioning primary on "prime" and a functioning standby server running on "standby." You can confirm the master knows about the standby, and that it is keeping it current, by running the following on the master:
psql -x -d pgbench -c "SELECT * FROM repmgr_test.repl_status"
Some tests you might do at this point include:
- Insert some records into the primary server here, confirm they appear very quickly (within milliseconds) on the standby, and that the repl_status view advances accordingly.
- Verify that you can run queries against the standby server, but cannot make insertions into the standby database.
To simulate the loss of the primary server, simply stop the "prime" server. At this point, the standby contains the database as it existed at the time of the "failure" of the primary server.
Now you can promote the standby server to be the primary, to allow applications to read and write to the database again, by typing:
repmgr -f /home/standby/repmgr/repmgr.conf --verbose standby promote
The server restarts and now has read/write ability.
To make the former primary act as a standby, which is necessary before restoring the original roles, type:
repmgr -U standby -R prime -h 127.0.0.1 -p 5433 -d testdb --force --verbose standby clone
Stop and restart the "prime" server, which is now acting as a standby server.
Make sure the record(s) inserted the earlier step are still available on the now standby (prime). Confirm the database on "prime" is read-only.
Now restore to the original configuration by stopping the
"standby" (now acting as a primary), promoting "prime" again to be the
primary server, then bringing up "standby" as a standby with a valid
recovery.conf file on "standby".
Stop the "standby" server:
repmgr -f /home/prime/repmgr/repmgr.conf standby promote
Now the original primary, "prime" is acting again as primary.
Start the "standby" server and type this on "prime":
repmgr standby clone --force -h 127.0.0.1 -p 5434 -U prime -R standby --verbose
Stop the "standby" and change the port to be 5434 in the postgresql.conf
file.
Verify the roles have reversed by attempting to insert a record on "standby" and on "prime."
The servers are now again acting as primary on "prime" and standby on "standby".
repmgr.conf is looked for in the directory repmgrd or repmgr exists in.
The configuration file should have 3 lines:
- cluster: A string (single quoted) that identify the cluster we are on
- node: An integer that identify our node in the cluster
- conninfo: A string (single quoted) specifying how we can connect to this node's PostgreSQL service
The current supported syntax for the program can be seen using:
repmgr --help
The output from this program looks like this:
repmgr: Replicator manager
Usage:
repmgr [OPTIONS] master {register}
repmgr [OPTIONS] standby {register|clone|promote|follow}
General options:
--help show this help, then exit
--version output version information, then exit
--verbose output verbose activity information
Connection options:
-d, --dbname=DBNAME database to connect to
-h, --host=HOSTNAME database server host or socket directory
-p, --port=PORT database server port
-U, --username=USERNAME database user name to connect as
Configuration options:
-D, --data-dir=DIR local directory where the files will be copied to
-f, --config_file=PATH path to the configuration file
-R, --remote-user=USERNAME database server username for rsync
-w, --wal-keep-segments=VALUE minimum value for the GUC wal_keep_segments (default: 5000)
-I, --ignore-rsync-warning ignore rsync partial transfer warning
-F, --force force potentially dangerous operations to happen
repmgr performs some tasks like clone a node, promote it or making follow another node and then exits.
COMMANDS:
master register - registers the master in a cluster
standby register - registers a standby in a cluster
standby clone [node] - allows creation of a new standby
standby promote - allows manual promotion of a specific standby into a new master in the event of a failover
standby follow - allows the standby to re-point itself to a new master
The --verbose option can be useful in troubleshooting issues with
the program.
Not all of these commands need the repmgr.conf file, but they need to be able to
connect to the remote and local databases.
You can teach it which is the remote database by using the -h parameter or as a last parameter in standby clone and standby follow. If you need to specify a port different then the default 5432 you can specify a -p parameter. Standby is always considered as localhost and a second -p parameter will indicate its port if is different from the default one.
master register
- Registers a master in a cluster, it needs to be executed before any standby nodes are registered
standby register
- Registers a standby in a cluster, it needs to be executed before repmgrd will function on the node.
standby clone [node to be cloned]
Does a backup via
rsyncof the data directory of the primary. And it creates the recovery file we need to start a new hot standby server. It doesn't need therepmgr.confso it can be executed anywhere on the new node. You can change to the directory you want the new database cluster at and execute:./repmgr standby clone node1
or run from wherever you are with a full path:
./repmgr -D /path/to/new/data/directory standby clone node1
That will make a backup of the primary then you only need to start the server using a command like:
pg_ctl -D /your_data_directory_path start
Note that some installations will also redirect the output log file when executing
pg_ctl; check the server startup script you are using and try to match what it does.
standby promote
Allows manual promotion of a specific standby into a new primary in the event of a failover. This needs to be executed on the same directory where the
repmgr.confis in the standby, or you can use the-foption to indicate where therepmgr.confis at. It doesn't need any additional arguments:./repmgr standby promote
That will restart your standby postgresql service.
standby follow
Allows the standby to base itself to the new primary passed as a parameter. This needs to be executed on the same directory where the
repmgr.confis in the standby, or you can use the-foption to indicate where therepmgr.confis at. Example:./repmgr standby follow
The current supported syntax for the program can be seen using:
repmgrd --help
The output from this program looks like this:
repmgrd: Replicator manager daemon Usage: repmgrd [OPTIONS] Options: --help show this help, then exit --version output version information, then exit --verbose output verbose activity information -f, --config_file=PATH database to connect to repmgrd monitors a cluster of servers.
The --verbose option can be useful in troubleshooting issues with
the program.
repmgrd reads the repmgr.conf file in current directory, or as
indicated with -f parameter. If run on a standby, it checks if that
standby is in repl_nodes and adds it if not.
Before you can run repmgrd you need to register a master in a cluster
using the MASTER REGISTER command. If run on a master,
repmgrd will exit, as it has nothing to do on them yet. It is only
targeted at running on standby servers currently. If converting
a former master into a standby, you will need to start repmgrd
in order to make it fully operational in its new role.
The repmgr daemon creates 2 connections: one to the master and another to the standby.
repmgrd helps monitor a set of master and standby servers. You can see which node is the current master, as well as how far behind each is from current.
To look at the current lag between primary and each node listed
in repl_node, consult the repl_status view:
psql -d postgres -c "SELECT * FROM repmgr_test.repl_status"
This view shows the latest monitor info from every node.
- replication_lag: in bytes. This is how far the latest xlog record we have received is from master.
- apply_lag: in bytes. This is how far the latest xlog record we have applied is from the latest record we have received.
- time_lag: in seconds. How many seconds behind the master is this node.
When the repmgr or repmgrd program exits, it will set one of the following
- SUCCESS 0: Program ran successfully.
- ERR_BAD_CONFIG 1: One of the configuration checks the program makes failed.
- ERR_BAD_RSYNC 2: An rsync call made by the program returned an error.
- ERR_STOP_BACKUP 3: A
pg_stop_backup()call made by the program didn't succeed. - ERR_NO_RESTART 4: An attempt to restart a PostgreSQL instance failed.
- ERR_NEEDS_XLOG 5: Could note create the
pg_xlogdirectory when cloning. - ERR_DB_CON 6: Error when trying to connect to a database.
- ERR_DB_QUERY 7: Error executing a database query.
- ERR_PROMOTED 8: Exiting program because the node has been promoted to master.
- ERR_BAD_PASSWORD 9: Password used to connect to a database was rejected.
repmgr is licensed under the GPL v3. All of its code and documentation is Copyright 2010-2011, 2ndQuadrant Limited. See the files COPYRIGHT and LICENSE for details.
Main sponsorship of repmgr has been from 2ndQuadrant customers.
Additional work has been sponsored by the 4CaaST project for cloud computing, which has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement 258862.
Contributions to repmgr are welcome, and will be listed in the file CREDITS. 2ndQuadrant Limited requires that any contributions provide a copyright assignment and a disclaimer of any work-for-hire ownership claims from the employer of the developer. This lets us make sure that all of the repmgr distribution remains free code. Please contact info@2ndQuadrant.com for a copy of the relevant Copyright Assignment Form.
Code in repmgr is formatted to a consistent style using the following command:
astyle --style=ansi --indent=tab --suffix=none *.c *.h
Contributors should reformat their code similarly before submitting code to the project, in order to minimize merge conflicts with other work.
2ndQuadrant provides 24x7 production support for repmgr, as well as help you configure it correctly, verify an installation and train you in running a robust replication cluster.
There is a mailing list/forum to discuss contributions or issues http://groups.google.com/group/repmgr
#repmgr is registered in freenode IRC
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 info@2ndQuadrant.com, or send a postcard to
repmgr c/o 2ndQuadrant 7200 The Quorum Oxford Business Park North Oxford OX4 2JZ
Thanks from the repmgr core team
Jaime Casanova Simon Riggs Greg Smith Cedric Villemain