Why can’t I point my clients to the DAG Cluster IP?

I was reminded today of a question I used to see a lot in the forums. Not so much anymore, but perhaps a refresher is in order.

Granted, it seems almost brilliant to simply configure all the URLs and connection points to the DAG IP. And after all it does say its use is “Cluster and Client”¬† ūüėõ

capture

and if that means there is no need to worry about load balancing and let Exchange handle it, then why not?

Here’s Why:.

  1. There is no Exchange dependency on the Cluster IP being online. Both Exchange 2013 and Exchange 2016 support IP-Less Database Availability Groups.¬†The cluster IP can go offline and¬†Exchange will run just fine.¬†The only real reason to assign a¬†Cluster IP address is if you are using backup software or another 3rd party application that requires it. If you run Exchange with the Preferred Architecture recommendations, you¬†won’t be doing backups anyway!
  2. If the Cluster name goes offline and the IP with it, Managed Availability won’t attempt to bring it online. That¬†requires manual intervention. Yuck.
  3. The Cluster IP is held by a specific mailbox server in the DAG at any one time – meaning all client connections will go through that multi-role server and no others.
  4. If the quorum owner moves to another server, there is no guarantee that the clients will handle that gracefully.
  5. The only way to prevent a server from end-user client access in this scenario is to pause or stop the cluster service on the affected server.
  6. IT’S NOT SUPPORTED!

 

 

 

 

 

Recommended Reading

Discuss