Need advice on keeping backup database up to date

I have been using postgresql for my web application for a while now and
it has been great.

I want to set up a separate emergency failover server and database in a
different data center.

In the event that my primary data center becomes inaccessible, I want to
update a DNS record and then redirect visitors to the backup data
center.

I am trying to figure out how I can keep the postgresql database in the
backup data center as up to date as possible.

The ideal solution would keep the backup database updated in real time
as the primary database changes.

I need advice about the best way to accomplish this.

Thanks in advance.


Matt