Use ZenLoadBalancer 3.0.3 with Hyper-V 2012/SCVMM 2012 to load-balance Exchange 2010 CAS array

High availability should be a goal for any environment, but when you are the sole sysadmin and have to balance a second job role at the same time, it is key to protecting your sanity!

Here is what is entailed in creating a highly available Exchange 2010 environment. Our goal is to allow for one server to completely fail without disrupting clients or losing any email.

1. Make sure you are using Server 2008R2 Enterprise or Datacenter, or Server 2012 with Exchange 2010 SP3. Create at least two servers holding the mailbox role. If you desire, these servers can also host the CAS and Hub Transport roles.
2. Create a Database Availability Group.
3. Create a CAS array. Choose a DNS name for the CAS array, such as casarray.domain.local.
1. If you didn’t start out using the CAS array (like me), you will need to find a method of updating the profile on each client so they are aware of the CAS array. I created a profile using the Office setup wizard and then pushed it out to clients using GPP.
2. Assign the CAS array object to each database so that newly created profiles will point to the right place.
3. Make sure that the appropriate certificates are installed on each CAS server. Here, it is very helpful to use a SAN (subject alternative name) certificate as it is not keyed to a particular IP address.
4. Set up load balancing for the CAS array.

The standard approach is to use Windows Network Load Balancing. However, Microsoft no longer recommends this.

The key limitation that resonated with me is that adding a new NLB node will disrupt the existing cluster. This makes it very hard to create your NLB cluster without downtime. For other small environments without a separate mailbox and client access server, a third-party load balancer is the only option. Failover cluster (used by a DAG) can’t coexist with Network Load Balancing. So, you need to use 4 servers instead of 2, and many smaller environments may not have the server resources or licenses for this approach. Using a separate load balancer will allow you to have just two servers with combined mailbox/cas/hub transport roles.

After doing some research on the available load balancing options, I settled on ZenLoadBalancer. There are several (resolvable) roadblocks you can run into during the setup, none of which I found to be easy to research online, at least not all in one place.

• The Hyper-V support is not included in the default install.
• There is little up-to-date documentation.
• Clustering doesn’t work in a default install on Hyper-V.