mirror of
https://github.com/EnterpriseDB/repmgr.git
synced 2026-03-23 07:06:30 +00:00
57aa95f674
want to clone or connect to, instead of relying on the fact that for some time putting that argument at last worked.
214 lines
7.2 KiB
ReStructuredText
214 lines
7.2 KiB
ReStructuredText
=====================================================
|
|
PostgreSQL Automatic Fail-Over - User Documentation
|
|
=====================================================
|
|
|
|
Automatic Failover
|
|
==================
|
|
|
|
repmgr allows setups for automatic failover when it detects the failure of the master node.
|
|
Following is a quick setup for this.
|
|
|
|
Installation
|
|
============
|
|
|
|
For convenience, we define:
|
|
|
|
* node1 is the hostname fully qualified of the Master server, IP 192.168.1.10
|
|
* node2 is the hostname fully qualified of the Standby server, IP 192.168.1.11
|
|
* witness is the hostname fully qualified of the server used for witness, IP 192.168.1.12
|
|
|
|
:Note: It is not recommanded to use name defining status of a server like «masterserver»,
|
|
this is a name leading to confusion once a failover take place and the Master is
|
|
now on the «standbyserver».
|
|
|
|
Summary
|
|
-------
|
|
|
|
2 PostgreSQL servers are involved in the replication. Automatic fail-over need
|
|
to vote to decide what server it should promote, thus an odd number is required
|
|
and a witness-repmgrd is installed in a third server where it uses a PostgreSQL
|
|
cluster to communicate with other repmgrd daemons.
|
|
|
|
1. Install PostgreSQL in all the servers involved (including the server used for
|
|
witness)
|
|
2. Install repmgr in all the servers involved (including the server used for witness)
|
|
3. Configure the Master PostreSQL
|
|
4. Clone the Master to the Standby using "repmgr standby clone" command
|
|
5. Configure repmgr in all the servers involved (including the server used for witness)
|
|
6. Register Master and Standby nodes
|
|
7. Initiate witness server
|
|
8. Start the repmgrd daemons in all nodes
|
|
|
|
:Note: A complete Hight-Availability design need at least 3 servers to still have
|
|
a backup node after a first failure.
|
|
|
|
Install PostgreSQL
|
|
------------------
|
|
|
|
You can install PostgreSQL using any of the recommended methods. You should ensure
|
|
it's 9.0 or superior.
|
|
|
|
Install repmgr
|
|
--------------
|
|
|
|
Install repmgr following the steps in the README.
|
|
|
|
Configure PostreSQL
|
|
-------------------
|
|
|
|
Log in node1.
|
|
|
|
Edit the file postgresql.conf and modify the parameters::
|
|
|
|
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
|
|
shared_preload_libraries = 'repmgr_funcs'
|
|
|
|
Edit the file pg_hba.conf and add lines for the replication::
|
|
|
|
host repmgr repmgr 127.0.0.1/32 trust
|
|
host repmgr repmgr 192.168.1.10/30 trust
|
|
host replication all 192.168.1.10/30 trust
|
|
|
|
:Note: It is also possible to use a password authentication (md5), .pgpass file
|
|
should be edited to allow connection between each node.
|
|
|
|
Create the user and database to manage replication::
|
|
|
|
su - postgres
|
|
createuser -s repmgr
|
|
createdb -O repmgr repmgr
|
|
psql -f /usr/share/postgresql/9.0/contrib/repmgr_funcs.sql repmgr
|
|
|
|
Restart the PostgreSQL server::
|
|
|
|
pg_ctl -D $PGDATA restart
|
|
|
|
And check everything is fine in the server log.
|
|
|
|
Create the ssh-key for the postgres user and copy it to other servers::
|
|
|
|
su - postgres
|
|
ssh-keygen # /!\ do not use a passphrase /!\
|
|
cat ~/.ssh/id_rsa.pub > ~/.ssh/authorized_keys
|
|
chmod 600 ~/.ssh/authorized_keys
|
|
exit
|
|
rsync -avz ~postgres/.ssh/authorized_keys node2:~postgres/.ssh/
|
|
rsync -avz ~postgres/.ssh/authorized_keys witness:~postgres/.ssh/
|
|
rsync -avz ~postgres/.ssh/id_rsa* node2:~postgres/.ssh/
|
|
rsync -avz ~postgres/.ssh/id_rsa* witness:~postgres/.ssh/
|
|
|
|
Clone Master
|
|
------------
|
|
|
|
Log in node2.
|
|
|
|
Clone the node1 (the current Master)::
|
|
|
|
su - postgres
|
|
repmgr -d repmgr -U repmgr -h node1 standby clone
|
|
|
|
Start the PostgreSQL server::
|
|
|
|
pg_ctl -D $PGDATA start
|
|
|
|
And check everything is fine in the server log.
|
|
|
|
Configure repmgr
|
|
----------------
|
|
|
|
Log in each server and configure repmgr by editing the file
|
|
/etc/repmgr/repmgr.conf::
|
|
|
|
cluster=my_cluster
|
|
node=1
|
|
node_name=earth
|
|
conninfo='host=192.168.1.10 dbname=repmgr user=repmgr'
|
|
master_response_timeout=60
|
|
reconnect_attempts=6
|
|
reconnect_interval=10
|
|
failover=automatic
|
|
promote_command='promote_command.sh'
|
|
follow_command='repmgr standby follow -f /etc/repmgr/repmgr.conf'
|
|
|
|
* *cluster* is the name of the current replication.
|
|
* *node* is the number of the current node (1, 2 or 3 in the current example).
|
|
* *node_name* is an identifier for every node.
|
|
* *conninfo* is used to connect to the local PostgreSQL server (where the configuration file is) from any node. In the witness server configuration it is needed to add a 'port=5499' to the conninfo.
|
|
* *master_response_timeout* is the maximum amount of time we are going to wait before deciding the master has died and start failover procedure.
|
|
* *reconnect_attempts* is the number of times we will try to reconnect to master after a failure has been detected and before start failover procedure.
|
|
* *reconnect_interval* is the amount of time between retries to reconnect to master after a failure has been detected and before start failover procedure.
|
|
* *failover* configure behavior : *manual* or *automatic*.
|
|
* *promote_command* the command executed to do the failover (including the PostgreSQL failover itself). The command must return 0 on success.
|
|
* *follow_command* the command executed to address the current standby to another Master. The command must return 0 on success.
|
|
|
|
Register Master and Standby
|
|
---------------------------
|
|
|
|
Log in node1.
|
|
|
|
Register the node as Master::
|
|
|
|
su - postgres
|
|
repmgr -f /etc/repmgr/repmgr.conf master register
|
|
|
|
Log in node2.
|
|
|
|
Register the node as Standby::
|
|
|
|
su - postgres
|
|
repmgr -f /etc/repmgr/repmgr.conf standby register
|
|
|
|
Initialize witness server
|
|
-------------------------
|
|
|
|
Log in witness.
|
|
|
|
Initialize the witness server::
|
|
|
|
su - postgres
|
|
repmgr -d repmgr -U repmgr -h 192.168.1.10 -D $WITNESS_PGDATA -f /etc/repmgr/repmgr.conf witness create
|
|
|
|
It needs information to connect to the master to copy the configuration of the cluster, also it needs to know where it should initialize it's own $PGDATA.
|
|
As part of the procees it also ask for the superuser password so it can connect when needed.
|
|
|
|
Start the repmgrd daemons
|
|
-------------------------
|
|
|
|
Log in node2 and witness.
|
|
|
|
su - postgres
|
|
repmgrd -f /etc/repmgr/repmgr.conf > /var/log/postgresql/repmgr.log 2>&1
|
|
|
|
:Note: The Master does not need a repmgrd daemon.
|
|
|
|
|
|
Suspend Automatic behavior
|
|
==========================
|
|
|
|
Edit the repmgr.conf of the node to remove from automatic processing and change::
|
|
|
|
failover=manual
|
|
|
|
Then, signal repmgrd daemon::
|
|
|
|
su - postgres
|
|
kill -HUP `pidoff repmgrd`
|
|
|
|
TODO : -HUP configuration update is not implemented and it should check its
|
|
configuration file against its configuration in DB, updating
|
|
accordingly the SQL conf (especialy the failover manual or auto)
|
|
this allow witness-standby and standby-not-promotable features
|
|
and simpler usage of the tool ;)
|
|
|
|
Usage
|
|
=====
|
|
|
|
The repmgr documentation is in the README file (how to build, options, etc.)
|