[Twisted-Python] Twisted HTTP client supporting failover for multiple A records?

Luke Marsden luke-lists at hybrid-logic.co.uk
Fri Jul 16 15:24:13 EDT 2010

Hi David,

> That's not to say using multiple A records isn't a helpful practice
> for many sorts of outages (especially to permit controlled
> maintenance).  Just don't expect it to necessarily be sufficient in
> all failure modes depending on the behavior you want clients to
> experience.

Indeed, in our application it's considered an optimisation over DNS
failover. This is why we also use a low TTL (30 seconds) to purge the
bad A records out of the pool as soon as possible.

> If this is strictly limited to a client you control, it's much less of
> an issue, since you can drop the TCP connect timeout much lower than
> what it defaults to, though you still probably can't match how fast it
> can happen for rejected connections, since you'll want to leave enough
> room for occasional latency or response time issues without
> immediately failing over.  But you can do a lot better than the system
> defaults.

Unfortunately we have no control over the clients' configuration (this
is a LAMP web hosting environment). But 30 seconds is considered much
more acceptable than the days it can often take a manual repair job if a
server goes down.

Best Regards,
Luke Marsden
Hybrid Logic Ltd.

Web: http://www.hybrid-cluster.com/
Hybrid Web Cluster - cloud web hosting based on FreeBSD and ZFS

Mobile: +447791750420

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