Microsoft Exchange 2010 CAS Array Non-Hardware Load Balancing Options

Posted on 2013-01-16
Last Modified: 2016-10-25
We are in the process of migrating from Exchange 2003 to Exchange 2010.  We have 3 Exchange 2010 VMs that all have Transport, Client Access, and Mailbox roles on them.  We recently realized that it's not supported to use Windows NLB on these VMs for our CAS Array since we're already using Windows Clustering for our DAG on the same servers.  We're trying to figure out what our best solution would be moving forward.  We currently have 4 Exchange 2010 server licenses so we could in theory add one additional Exchange 2010 VM, but we're not desirous of having more than 4 Exchange servers.

I've taken a look at both the Citrix Netscaler VPX Express and the Kemp LoadMaster virtual load balancers.  I was turned off on the Citrix one by their lack of documentation for their recent versions of the virtual appliance.  As for Kemp, I didn't really like that I had to leave a message when I called them for support, and then wait almost 2 hours to hear back from someone.

Right now, I'm configuring Steve Goodman's Exchange 2010 HA Proxy VM (from to see if that will work well enough for us.  Has anyone had any experience with that?  

We need a solution that is going to work well across our MPLS WAN, hopefully without having to ask AT&T to add a static arp entry to our router at each of our sites for clients to be able to reach the CAS.  I should add, all three of the current Exchange 2010 servers are on separate ESXi hosts in one location.


Question by:rschnitzer
LVL 28

Expert Comment

by:Ryan McCauley
ID: 38784616
If you've got a load balancer in place, you'll need to direct your traffic there, and it acts as a single point of contact - even if you're running three exchange VMs and the load balancer levels traffic to all three of them, traffic still has to hit the balancer first. The solution you link to looks like it would meet your needs, though I've never used it.
LVL 63

Accepted Solution

Simon Butler (Sembee) earned 500 total points
ID: 38784661
I have deployed the Zen Load Balancer in a couple of locations now. It is open source, but you can get commercial support for that. That is the major advantage over Steve's solution, which I think he says isn't really designed for production use.

However you don't have to use a load balancer with a RPC CAS Array. If you are happy to move the DNS entry manually then you can just point the DNS entry at a live CAS role holder and then when it goes down move it. I have seen a script that will check the server is available and change the DNS entry for you if you wish.


Author Comment

ID: 38805324
We've been using Steve's solution for half a week now, and no problems so far.  Hopefully, it will continue to work well for us.

- R

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