Tuesday, May 22, 2012

Exchange 2010 High Availability without Hardware Load Balancer

Achieve High Availability without hardware load balancer on Exchange 2010 with two DAG members

1. Create the DAG as normal.
2. Run the new-CASArray PS command…adding both servers to the array.
3. Go into DNS and create a CNAME record matching the CASArray name…pointing to the DAG name
4. Set the TTL of the records to 5 minutes (for cross-site IP address notification).
5. Set the URLs for all the internal and external to point to the CASArray name.
6. Get a UC cert with the common name matching the CASArray name.
7. Add autodiscover…and each FQDN of both servers as Subject Alternate Names.

That’s it. Failover happens within site in about 5 seconds (clients show a brief disconnect/reconnect…that’s all). Cross site failover occurs within ~5 minutes (due to the DAG claiming a new IP and the TTL of the DNS record cache flush occurring). No $20k BigIP boxes needed. No Cisco IOS commands. No complicated scripts or scheduling event. Certainly no need for a separate NLB array costing thousands…and thousands more dollars.
The only difference in this scenario is that the CASArray doesn’t load balance…it always prefers the current Active DAG member. Which…for most companies <1000 users…is perfectly acceptable. Other than that…it's incredibly less expensive…and much less complicated to setup and/or troubleshoot.