Exchange 2013 Client Access HA via two-datacenters

Hi folks,

I'm wondering how to make the following a nice HA solution:

- 2 Datacenters on different locations
- On each DC there is a complete Exchange 2013 Infrastructure with dedicated ClientAccess Servers and dedicated Mailbox Servers with DAG

How to make CAS HA in case of DC blackout?

1st idea:

- DNS Round Robin to client access server (con in case everything's fine = 50% of the client requests may contact the wrong CAS first, con in case of failover = client requests won't be answered if contacting failed server, 20 seconds timeout then retry other IP)

How do you recommend make CAS an reliable deployment?

Regards and tia
Marcel