Load Balancing TFS Code Search Servers
At this time, it is NOT possible to load balance the TFS Code Search servers (Elasticsearch) as the service is not designed for load balancing. TFS supports a single Code Search server in the TFS environment.
The Code Search service is considered an ancillary service to TFS and would not impact the developers ability to complete source control check-in/out and other actions to deliver code if the server hosting the server were to go offline.
Here are instructions on how to setup multiple Application Tiers (AT) and configuring Code Search with multiple ATs in the TFS environment: