Perlbal and sessions.

[christopher at baus.net]

> State is accessible from every node.  Requests come in with a session
> cookie, and the web node asks memcache to see if it knows anything about
> that session.  It falls back on the databases if memcache has no
> information on that cookie.
>
> Most of our infrastructure is replaceable and non-unique.  Our storage
> nodes are all duplicated through Mogile, our load balancers are identical,
> our web nodes all do the same things, etc.  The only parts of the system
> that can't just be swapped out at will are the databases -- but they get
> redundancy through having two machines doing the same load with only one
> active at a time.

Interesting.  I really like that architecture because it is simple, but
effective.  I believe some of the high end load balancers have the ability
to maintain connections even if a load balancer node catches fire.  With
perlbal I guess you'll still drop the connections that are active on that
proxy server.  Although that probably isn't that big of a deal given the
application.  Web users are used to hitting refresh anyway.