I can’t see why IS would care what network equipment (load balancer, XML appliance, router, global server load balancing (gslb) device) is upstream of it so long as the request arrives intact and there is a mechanism to provide “stickiness” in the event that you are (probably unwisely) building stateful services.
There are open source load balancing modules that can be plugged into most http servers or installed into Linux or Windows-based servers.
Keep in mind, though, that any load balancing component upstream of IS should have a good HA strategy to avoid becoming a new single point of failure (SPOF).
HTH,
Mark
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