SharePoint 2010 Application server Load Balancer

Question:

I've been tasked with setting up a 3-tier SharePoint farm.

1. Two load balanced webservers
2. Two applications servers
3. A SQL server

Everything is all set up and working with load balancing etc. etc.

My question is what do I do with the application servers?

• Do I load balance the two application servers?
• Do I cluster them?
• Do I run certain services on each server?
• Do I have the same services running on each server and SharePoint automatically chooses a server?

I'm not quite sure why we have two application servers. Currently I just have the same services running on each app server.

Answers: 

1. What you do with the application servers largely depends on what services you are running in the    farm and how heavy they are utilized (i.e. it depends on your requirements). SharePoint 2010 will handle it's own internal load balancing with the service applications, so no need to set those up behind  a load balancer. It just depends which application servers you have activated to run those services.

2. You do want to load balance the web front ends, but you do not want to load balance or cluster the Application Servers. The App servers should be where you run your Service Applications. These Service Applications can be started on more than one server. When they are started automatically on more than one server they are load balanced between the 2 app servers. If one goes down the server gets marked down and the other server handles the load by itself. When the other server comes back up it will eventually get marked as active again and load balancing will resume. I agree the query role should be located on the WFE. However in your situation I would run the Indexing Service on both App servers along with almost all of the other services so you get performance and redundancy.

3. SharePoint servers that hold roles such as search are typically labeled as application servers. These servers do not require load-balancing technology, since SharePoint provides load-balancing internally for service applications. In reality, servers labeled as either WFE servers or application servers may hold many different roles. For example, it is common for the search query role to be configured on WFE servers.
Reference:

http://www.microsofttechnology.net/2013/04/sharepoint-2010-application-server-load.html