How can we plan for a High Avialblity in Postgresql 9.3?

I am working for mission critical project.

We are palnning for High Availblity.At any point of time irrespective of the failure(n/w,Hw or db) one db server should be avilable for Application.

Scenario

A replicates to B(hot_standby)

if A goes down i can connect to B.Mean while after some time A has come up again how we can replicate from B to A.If we bring up A how can we bring it up either as old master or new slave to the master B.

One more clarification And also i am planning for Disaster recovery.Can it possible to enable wal archiving on both master A and slave B before starting replication.

And can we automate this whole procedure.I mean no manual intervention is required while replicating A from B(A is master) and B from A(B is master).

I am using OS redhat

Postgres Version 9.3.

Please help me in this.