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157 lines
4.8 KiB
Plaintext
157 lines
4.8 KiB
Plaintext
repmgr daemon
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==================================================================
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repmgr: Replication Manager for PostgreSQL's clusters
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=====================================================
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Introduction
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============
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PostgreSQL 9.0 allow us to have replicated hot standby servers
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which we can query and/or use for high availability.
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While the main components of the feature are included with
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PostgreSQL, the user is expected to manage the high availability
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part of it.
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repmgr allows you to monitor and manage your replicated PostgreSQL
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databases as a single cluster.
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repmgr works in two components:
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* repmgr: command program that performs tasks and then exits
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* repmgrd: management and monitoring daemon that watches cluster
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COMMANDS
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========
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None of this commands need the repmgr.conf file but they need to be able to
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connect to the remote and local database.
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You can teach it which is the remote database by using the -h parameter or
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as a last parameter in standby clone and standby follow. If you need to specify
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a port different then the default 5432 you can specify a -p parameter.
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Standby is always considered as localhost and a second -p parameter will indicate
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its port if is different from the default one.
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* master register
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Registers a master in a cluster, it needs to be executed before any node is
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registered
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* standby register
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Registers a standby in a cluster, it needs to be executed before any repmgrd
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is executed
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* standby clone [node to be cloned]
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Backup via rsync the data directory of the primary. And creates the recovery file
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we need to start a new hot standby server.
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It doesn't need the repmgr.conf so it can be executed anywhere in the new node.
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So, you can step where you want your new data directory and execute:
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./repmgr standby clone 10.68.1.161
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or from wherever you are
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./repmgr -D /path/to/new/data/directory standby clone 10.68.1.161
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That will make a backup of the primary then you only need to execute:
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pg_ctl -D /your_data_directory_path start
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* standby promote
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Allows manual promotion of a specific standby into a new primary in the event of a failover
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This needs to be executed on the same directory where the repmgr.conf is in the standby or
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then use the -f option to indicate where the repmgr.conf is.
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Doesn't need any additional arguments:
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./repmgr standby promote
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That will restart your standby postgresql service
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* standby follow
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Allows the standby to re-point itself to a new primary indicated as a parameter.
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This needs to be executed on the same directory where the repmgr.conf is in the standby or
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then use the -f option to indicate where the repmgr.conf is.
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./repmgr standby follow
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PRE-REQUISITES
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==============
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Primary must be configured with
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postgresql.conf
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---------------
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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 .'
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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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Also you need to add the machines that will participate in the cluster in pg_hba.conf.
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ie:
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host all all 10.8.0.0/24 trust
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host replication all 10.8.0.0/24 trust
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EXAMPLES
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========
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Suppose we have 3 nodes: node1 (the master), node2 and node3
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To make node2 and node3 be standbys of node1, execute this on both nodes (node2 and node3):
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repmgr -D /var/lib/postgresql/9.0 standby clone node1
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If we lose node1 we can run on node2:
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repmgr -f /home/postgres/repmgr.conf standby promote
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which makes node2 the new master, we then run on node3:
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repmgr standby follow
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to make node3 follow node2 (rather than node1)
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If now we want to add a new node we can a prepare a new server (node4) and run:
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repmgr -D /var/lib/postgresql/9.0 standby clone node2
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NOTE: you need to have PGDIR/bin in your path, if you don't want that as a
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permanent setting you can do it this way:
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PATH=$PGDIR/bin:$PATH repmgr standby promote
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CONFIGURATION FILE
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==================
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repmgr.conf: This is looked for in the directory repmgrd or repmgr exists
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The configuration file should have 3 lines:
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cluster : tha name of this cluster
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node : specify the number of this node inside the cluster
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conninfo: specify how we can connect to this node's PostgreSQL service
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REPMGR DAEMON
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=============
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It reads the repmgr.conf file in current directory or as indicated with -f
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parameter looks if the standby is in repl_nodes and if it is not add it.
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Before you can run the repmgr daemon (repmgrd) you need to register a master
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and at least a standby in a cluster, for that you need to use the MASTER
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REGISTER and STANDBY REGISTER commands.
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For example, following last example and assuming that repmgr.conf is in postgres
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home directory you will run this on the master:
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repmgr -f /home/postgres/repmgr.conf master register
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and the same in the standby.
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The repmgr daemon creates 2 connections: one to master and other to standby.
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