Azimuddin,
Then you should look at the tools you have at hand. i.e. Using nothing but the OS (FreeBSD/CARP/ZFS), Postgres and some custom scripts.
In the postgres.conf file setup synchronous replication and the application_name in the recovery.conf file:
synchronous_standby_names = '1 (standby, witness)'
----------- -----------
| | | |
| primary |---sync--->| standby |
| | | |
----------- -----------
| |
| |
---------carp-----------
|
|
async/sync
|
|
-----------
| |
| witness |
| |
-----------
