Load Balancing

processing of passing network requests through a single point, which passes them along to one out of a cluster of ultimate servers

Often done with cluster of Web Server-s (which all speak to a single Data Base server)

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?

• Apache 'mod_proxy_balancer'

• Balance - http://www.linux.com/article.pl?sid=05/07/27/1729229

  • Balance Ng - http://www.inlab.de/balance.html

• http://blogs.law.harvard.edu/philg/2006/11/06/best-open-source-software-for-a-firewallload-balancer/

Dec'2012 recommendations from some friends (coming from context of running SSL in the Load Balancer): if "in the cloud", do not use Amazon ELB

• 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).