High Availability PostgreSQL HOWTO

　　Introduction:

　　This note describes ways to implement High Availibility (HA) for PostgreSQL. HA gives the ability to transparently fail-over database connections to an alternative system in the event of some sort of failure of the primary system.

　　Overview:

　　The HA-PostgreSQL system works the following way: The HA cluster consists of two machines running heartbeat that use both a serial port and a second network interface to provide the failover heartbeat. The primary system keeps the secondary system database files synchronized by periodic calls to a script that runs rsync.

　　The heartbeat software provides HA in the form of a hot standby 2-node cluster. In the event of a failure of the primary database system, the heartbeat software causes the secondary to take over. Any database changes that may have occurred between the last synchronization and the failure will be lost, so this synchronization must be done relatively frequently. The synchronization is done with the same network interface that is also doing the heartbeat in order to reduce the volume of traffic on the primary network.

　　Setting up HA-PostgreSQL

　　Install heartbeat(http://linux-ha.org/) and get it running properly on the two systems. The installation should use both a serial connection and a secondary network interface (connected via a cross-over cable) to implement the heartbeat. In what follows, I will assume that the secondary network interface is eth1 on both systems and that 10.0.0.1 (hb-castor) is the primary system (castor) and 10.0.0.2 (hb-pollux) is the secondary system (pollux).