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repmgr: Replication Manager for PostgreSQL's clusters
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Introduction
============

PostgreSQL 9.0 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 works in two components:
* repmgr: command program that performs tasks and then exits
* repmgrd: management and monitoring daemon that watches cluster


COMMANDS
========

* standby clone [node to be cloned] 

Backup via rsync the data directory of the primary. And creates the recovery file
we need to start a new hot standby server.
It doesn't need the repmgr.conf so it can be executed anywhere in the new node.
So, you can step where you want your new data directory and execute:

./repmgr standby clone 10.68.1.161

That will make a backup of the primary then you only need to execute:

pg_ctl -D /your_data_directory_path start


* 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.conf is in the standby.
Doesn't need any additional arguments:

./repmgr standby promote

That will restart your standby postgresql service


* standby follow [node to be followed] 

Allows the standby to re-point itself to a new primary indicated as a parameter.
This needs to be executed on the same directory where the repmgr.conf is in the standby.

./repmgr standby follow 10.68.1.162


PRE-REQUISITES
==============

Primary must be configured with

postgresql.conf
---------------
listen_addresses='*'
wal_level = 'hot_standby'
archive_mode = on
archive_command = 'cd .'
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.
ie:
host     all              all         10.8.0.0/24         trust
host     replication      all         10.8.0.0/24         trust


Configuration file
==================

repmgr.conf: This is looked for in the directory repmgrd or repmgr exists
The configuration file should have 3 lines:
cluster : tha name of this cluster
node    : specify the number of this node inside the cluster
conninfo: specify how we can connect to this node's PostgreSQL service