> 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 abou=
t
> 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 identic=
al,
> our web nodes all do the same things, etc.  The only parts of the syste=
m
> that can't just be swapped out at will are the databases -- but they ge=
t
> redundancy through having two machines doing the same load with only on=
e
> 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 abilit=
y
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.

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