processing of passing network requests through a single point, which passes them along to one out of a cluster of ultimate servers
Needs to be able to determine the "health" of each server, and take unhealthy units out of the cluster: hit status page which provides rich definition of all-green.
If uses "sticky" mapping of user to a single server, you can store session-state on that server with "reasonable" safety.
Sometimes combined with FireWall.
Open Source options?
- you can now get some pretty decent Layer 7 load balancers (Netscaler announced a per hr pricing model, F5 will be announcing one soon & Riverbed (Sting Ray) has had one available for the longest time). I highly recommend leveraging a layer 7 load balancer and using it's built-in capabilities - I find them to help significantly reduce application complexity if you leverage all the features available (Cache, Gzip Compression, SSL Termination, Security, etc).
Edited: | Tweet this!