High availability question

[Sidney Shapiro]

I am running a hosting server currently equipped with a backup diesel
generator. Since the blackout, I have been considering a backup high
availability system, where if one would go out, the other would pick up
the slack. I have been told that this is impossible, and can only work
if I use a high availability scheme which would always keep one server
running.  

I have been told: "The expensive version of that would be to use the
akamai network, you could have both geographical load balancing and
near-instant failover. Otherwise, Youd have to build a cluster to start
with, there are a lot of ways to do this, and it depends on the service.
WWW for example is much easier to do than mail, you can use rsync to
keep the content up to date. Logfiles on the other hand would have to be
recombined and processed later on to do statistics. Another cheap way to
do this would be to set up a bunch of squid servers to proxy traffic to
your box. This wouldnt do anything for mail though, to keep that
together you'd need some kind of network file system, NFS, AFS or Coda
(qmail is NFS aware, which helps). You'd only need to store the user
mailboxes (/var/qmail/mailnames) on the network filesystem, Id keep the
queue on a local disk for performance reasons. For content, I'd
designate one system as the designated "master" for inbound content
(ftp, database, etc), and everything else mirrors that (rsync,
replication for mysql and postgres, etc). Databases would be the most
complex component, you'd have to work out your replication strategy to
break out how to do the inserts/updates without each system stepping on
each others toes."

Does anyone have an idea of how I could offer live (or rsynced to 2
hours) backup/live services for hosting. I would like if one server went
down, the other would take over. Is this possible?

Sid


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