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214 lines
7.2 KiB
ReStructuredText
214 lines
7.2 KiB
ReStructuredText
=====================================================
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PostgreSQL Automatic Fail-Over - User Documentation
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=====================================================
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Automatic Failover
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==================
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repmgr allows setups 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 is the hostname fully qualified of the Master server, IP 192.168.1.10
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* node2 is the hostname fully qualified of the Standby server, IP 192.168.1.11
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* witness is the hostname fully qualified of the server used for witness, IP 192.168.1.12
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:Note: It is not recommanded to use name defining status of a server like «masterserver»,
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this is a name leading to confusion once a failover take 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 fail-over need
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to vote to decide what server it should promote, thus an odd number is required
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and 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 server used for
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witness)
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2. Install repmgr in all the servers involved (including the server used for witness)
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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 server used for witness)
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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 Hight-Availability design need 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 superior.
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Install repmgr
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--------------
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Install repmgr following the steps in the README.
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Configure PostreSQL
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-------------------
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Log in 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 node2.
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Clone the node1 (the current Master)::
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su - postgres
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repmgr -d repmgr -U repmgr standby clone node1
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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 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* is the name of the current replication.
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* *node* is the number of the current node (1, 2 or 3 in the current example).
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* *node_name* is an identifier for every node.
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* *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.
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* *master_response_timeout* is the maximum amount of time we are going to wait before deciding the master has died and start failover procedure.
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* *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.
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* *reconnect_interval* is the amount of time between retries to reconnect to master after a failure has been detected and before start failover procedure.
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* *failover* configure behavior : *manual* or *automatic*.
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* *promote_command* 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* 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 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 node2.
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Register the node as 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 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 node1
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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.
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As part of the procees it also ask for the superuser password so it can connect when needed.
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Start the repmgrd daemons
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-------------------------
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Log in node2 and witness.
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su - postgres
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repmgrd -f /etc/repmgr/repmgr.conf > /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 `pidoff repmgrd`
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TODO : -HUP configuration update is not implemented and it should check its
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configuration file against its configuration in DB, updating
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accordingly the SQL conf (especialy the failover manual or auto)
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this allow witness-standby and standby-not-promotable features
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and simpler usage of the tool ;)
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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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