Replication
This is the nicest guide for streaming replication that I've found: Zero to PostgreSQL streaming replication in 10 mins. It is written for Ubuntu, but it only needs a couple of steps done differently on CentOS, which I have noted in the comments of that article. This guide is not as clear (for my preference), but it includes some commands to verify that the replication is running: How To Setup PostgreSQL Replication On CentOS.