It is recommended that you use an external instance of the vPostgres database for the CAFÉ appliance in a high availability (HA) environment. However, since the release of VMware vRealize Automation standalone, VMware vFabric Postgres is the end of availability and is no longer available as a standalone product. To address customers' needs, VMware developed a way to utilize the database instance located in the VMware vRealize Automation appliance in HA mode without having to incur additional licensing.
The following steps are clearly documented at http://kb.vmware.com/kb/2108923. We will follow exactly the same steps given here, with some screenshots for ease of understanding.