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I've seen the various posts about the software architecture and indeed the db hardware is documented too.

I've also seen a reference to HAProxy as the load balancing software.

What does HAProxy run on though? It appears to be running on a Linux box; is this correct? Or have some other Linux-based balancing appliance now been installed?

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26

Check out the Stack Overflow Network Configuration blog entry. Jeff talks a lot about how they are using HAProxy.

Network Config
(source: stackoverflow.com)

The HAProxy box is indeed linux. I'm not sure if it is still a virtualized instance, but it used to be. I assume that, since they now have redundant HAProxy boxes that there is at least one physical box doing load balancing.

The High Scalability Blog also has some details on this as well:
http://highscalability.com/blog/2009/8/5/stack-overflow-architecture.html

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  • Thats perfect, many thanks.
    – Codek
    Feb 18, 2010 at 15:53
  • Ah; I can't do the upvote as i dont have the rep yet, doh. Not sure why my rep on stack overflow doesnt apply here. but will when i can :)
    – Codek
    Feb 18, 2010 at 15:57
  • @Codek: You can get an "account association bonus" of 100 rep, but only when you have 200 rep on one of the associating sites. But apparently I see you have enough rep to vote in the mean time ;-)
    – fretje
    Feb 18, 2010 at 16:01
  • yup, it's gone up enough now, so i upvoted!
    – Codek
    Feb 18, 2010 at 16:03
  • Upvote for both, very nice q and a!
    – Mark Harrison
    Feb 19, 2010 at 3:50
  • I guess also, there's no SSL in the architecture? Is the SSL all done by the OpenID provider? Or is there some SSL on the webservers?
    – Codek
    Feb 19, 2010 at 10:50

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