Howtoforge posted a guide about setting up an active/passive PostgreSQL cluster with Pacemaker, Corosync, and DRBD under CentOS 5.5

This article explains how to set up (and monitor) an Active/Passive PostgreSQL Cluster, using Pacemaker with Corosync and DRBD. We use two nodes, one active (that answers requests from apps) and the other on passive mode. If the active server is down, the passive one will automatically take its position (being the active node). We are using the CentOS 5.5 (64bits) distribution, but it will probably work on Fedora (and Red Hat, for sure) as well.

  How To Set Up An Active/Passive PostgreSQL Cluster With Pacemaker, Corosync, And DRBD (CentOS 5.5)