[vidarh]

One approach I used when we migrated data centres to avoid having to manage timing etc. of IP address changes in our apps, was to use haproxy.

We configured slaves in the new data centre, set up a haproxy in the new data centre that used the old data centre databases as the main backend, and the new data centre databases as the backup, changed the apps to point to haproxy, shut down the masters and let haproxy shift all the traffic, promoted the slaves once we were certain they'd caught up. We had a period of seconds where the sites were effectively read-only, but that was it.

We're planning rolling out haproxy with keepalived or ucarp to mediate between a lot more of our backend services