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232 lines
6.8 KiB
ReStructuredText
232 lines
6.8 KiB
ReStructuredText
====================================================
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PostgreSQL Automatic Failover - User Documentation
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====================================================
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Automatic Failover
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==================
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repmgr allows for automatic failover when it detects the failure of the master node.
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Following is a quick setup for this.
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Installation
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============
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For convenience, we define:
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**node1**
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is the fully qualified domain name of the Master server, IP 192.168.1.10
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**node2**
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is the fully qualified domain name of the Standby server, IP 192.168.1.11
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**witness**
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is the fully qualified domain name of the server used as a witness, IP 192.168.1.12
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**Note:** We don't recommend using names with the status of a server like «masterserver»,
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because it would be confusing once a failover takes place and the Master is
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now on the «standbyserver».
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Summary
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-------
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2 PostgreSQL servers are involved in the replication. Automatic failover needs
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a vote to decide what server it should promote, so an odd number is required.
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A witness-repmgrd is installed in a third server where it uses a PostgreSQL
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cluster to communicate with other repmgrd daemons.
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1. Install PostgreSQL in all the servers involved (including the witness server)
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2. Install repmgr in all the servers involved (including the witness server)
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3. Configure the Master PostreSQL
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4. Clone the Master to the Standby using "repmgr standby clone" command
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5. Configure repmgr in all the servers involved (including the witness server)
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6. Register Master and Standby nodes
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7. Initiate witness server
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8. Start the repmgrd daemons in all nodes
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**Note** A complete High-Availability design needs at least 3 servers to still have
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a backup node after a first failure.
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Install PostgreSQL
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------------------
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You can install PostgreSQL using any of the recommended methods. You should ensure
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it's 9.0 or later.
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Install repmgr
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--------------
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Install repmgr following the steps in the README file.
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Configure PostreSQL
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-------------------
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Log in to node1.
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Edit the file postgresql.conf and modify the parameters::
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listen_addresses='*'
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wal_level = 'hot_standby'
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archive_mode = on
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archive_command = 'cd .' # we can also use exit 0, anything that
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# just does nothing
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max_wal_senders = 10
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wal_keep_segments = 5000 # 80 GB required on pg_xlog
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hot_standby = on
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shared_preload_libraries = 'repmgr_funcs'
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Edit the file pg_hba.conf and add lines for the replication::
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host repmgr repmgr 127.0.0.1/32 trust
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host repmgr repmgr 192.168.1.10/30 trust
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host replication all 192.168.1.10/30 trust
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**Note:** It is also possible to use a password authentication (md5), .pgpass file
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should be edited to allow connection between each node.
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Create the user and database to manage replication::
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su - postgres
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createuser -s repmgr
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createdb -O repmgr repmgr
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psql -f /usr/share/postgresql/9.0/contrib/repmgr_funcs.sql repmgr
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Restart the PostgreSQL server::
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pg_ctl -D $PGDATA restart
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And check everything is fine in the server log.
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Create the ssh-key for the postgres user and copy it to other servers::
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su - postgres
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ssh-keygen # /!\ do not use a passphrase /!\
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cat ~/.ssh/id_rsa.pub > ~/.ssh/authorized_keys
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chmod 600 ~/.ssh/authorized_keys
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exit
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rsync -avz ~postgres/.ssh/authorized_keys node2:~postgres/.ssh/
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rsync -avz ~postgres/.ssh/authorized_keys witness:~postgres/.ssh/
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rsync -avz ~postgres/.ssh/id_rsa* node2:~postgres/.ssh/
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rsync -avz ~postgres/.ssh/id_rsa* witness:~postgres/.ssh/
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Clone Master
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------------
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Log in to node2.
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Clone node1 (the current Master)::
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su - postgres
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repmgr -d repmgr -U repmgr -h node1 standby clone
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Start the PostgreSQL server::
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pg_ctl -D $PGDATA start
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And check everything is fine in the server log.
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Configure repmgr
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----------------
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Log in to each server and configure repmgr by editing the file
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/etc/repmgr/repmgr.conf::
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cluster=my_cluster
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node=1
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node_name=earth
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conninfo='host=192.168.1.10 dbname=repmgr user=repmgr'
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master_response_timeout=60
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reconnect_attempts=6
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reconnect_interval=10
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failover=automatic
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promote_command='promote_command.sh'
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follow_command='repmgr standby follow -f /etc/repmgr/repmgr.conf'
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**cluster**
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is the name of the current replication.
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**node**
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is the number of the current node (1, 2 or 3 in the current example).
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**node_name**
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is an identifier for every node.
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**conninfo**
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is used to connect to the local PostgreSQL server (where the configuration file is) from any node. In the witness server configuration you need to add a 'port=5499' to the conninfo.
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**master_response_timeout**
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is the maximum amount of time we are going to wait before deciding the master has died and start the failover procedure.
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**reconnect_attempts**
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is the number of times we will try to reconnect to master after a failure has been detected and before start the failover procedure.
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**reconnect_interval**
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is the amount of time between retries to reconnect to master after a failure has been detected and before start the failover procedure.
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**failover**
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configure behavior: *manual* or *automatic*.
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**promote_command**
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the command executed to do the failover (including the PostgreSQL failover itself). The command must return 0 on success.
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**follow_command**
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the command executed to address the current standby to another Master. The command must return 0 on success.
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Register Master and Standby
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---------------------------
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Log in to node1.
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Register the node as Master::
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su - postgres
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repmgr -f /etc/repmgr/repmgr.conf master register
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Log in to node2. Register it as a standby::
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su - postgres
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repmgr -f /etc/repmgr/repmgr.conf standby register
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Initialize witness server
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-------------------------
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Log in to witness.
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Initialize the witness server::
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su - postgres
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repmgr -d repmgr -U repmgr -h 192.168.1.10 -D $WITNESS_PGDATA -f /etc/repmgr/repmgr.conf witness create
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The witness server needs the following information from the command
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line:
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* Connection details for the current master, to copy the cluster
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configuration.
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* A location for initializing its own $PGDATA.
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It will also ask for the superuser password on the witness database so
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it can reconnect when needed.
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Start the repmgrd daemons
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-------------------------
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Log in to node2 and witness::
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su - postgres
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repmgrd -f /etc/repmgr/repmgr.conf --daemonize -> /var/log/postgresql/repmgr.log 2>&1
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**Note:** The Master does not need a repmgrd daemon.
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Suspend Automatic behavior
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==========================
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Edit the repmgr.conf of the node to remove from automatic processing and change::
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failover=manual
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Then, signal repmgrd daemon::
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su - postgres
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kill -HUP $(pidof repmgrd)
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Usage
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=====
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The repmgr documentation is in the README file (how to build, options, etc.)
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