Can I Load Balance 2010 CAS After Installing The Role On DAG Members?
I have read in a number of blog posts & forums that you can have a resilient & redundant 2010 messaging system with just two servers, making use of the new DAG functionality and the option to install CAS & HUB roles on the DAG members as well. This becomes a big driving factor for…
I have read in a number of blog posts & forums that you can have a resilient & redundant 2010 messaging system with just two servers, making use of the new DAG functionality and the option to install CAS & HUB roles on the DAG members as well. This becomes a big driving factor for people to upgrade from 2007, which needs atleast four servers to provide a redundant solution.
Though this is true, certain points need to be considered.
- You can install CAS & HUB roles on both DAG members
- But you cannot have them load balanced using NLB, as you cannot have both clustering and NLB running on the same servers.
- An external load balancer (not ISA server) becomes the option to configure a load balanced CAS array with just two servers.
- Once you have a load balancer, CAS array needs to be configured on all mailbox databases.
Many are not aware of this fact & hence thought of making it clear.
Thanks for the comment George Khalil.
Thanks for the clarification guys. A lot of forums (potentially some Microsoft ones as well) have mentioned ISA as a NLB alternative which I always thought was impossible in Exchange 2010 RPC access. Yes fair enough, ISA does a good job with http requests and have so for many years.
We are going down the path of utilising Windows NLB on 2 dedicated CAS boxes and Hub/Mail Box together in a DAG config.
Liran & Elan,
Thanks a lot for the comments with good explanation guys. I haven't checked my emails in days & hence the delay in replying.
As I was in the festive mood, I didn't double check my article, which I normally do. I have seen in many forums that you can use ISA to load balance CAS array & wanted to clear that issue.
But, instead of writing "not ISA server", I ended up writing "or ISA server".
Thanks for pointing it out guys! I have fixed the typo.
Liran, you are correct and Rajith will probably fix that in his article. You cannot use ISA to load balance RPC traffic, only HTTP. So, ISA is an option to load balance the HTTP traffic for the CAS Servers but you'll still need a load balancer for the RPC Client Accesss Array.
Even with two NICs, it wouldn't matter. ISA can only load balance HTTP traffic which you can do with 1 or 2 NICs. For other protocols, ISA can only publish via a 1:1 mapping. Having two NICs just allows you to publish things other than HTTP/FTP.
I don't understand how it is possible!
ISA Server can publish a web farm.
However…. CAS for Mapi clients needs to load balance port 135 and the returned high port.
A web publishing rule in intended for web content and reverse proxying. Not NLB. It is an NLB for web applications (Which CAS for MAPI is not)
Additionally, let say you want to use ISA. You will use it inside your network to "Load Balance" the CAS servers. The ISA server will only have one NIC with a listener since the ISA server and CAS servers are on the same network with a single NIC configuration.
With a single NIC no Firewall publishing can be done, only web… this will not work.
Another thing… ISA is 32bit and the Exchange servers are 64bit. Just imagine the load on the ISA server with all MAPI requests going through it. ISA will need to work hard on the application level and not the network level like a load balancer.
I don't think this can be done at all, and I would love to find out I'm wrong.