[users@httpd] Apache 2.2 mod_proxy TCP timeouts

[Ian Reynolds <ir...@symplicity.com>]

Hey everyone. We have been running Apache 2.2 as a reverse proxy cache
server for some time, and in general it performs great. We have one
nagging problem however.

Currently we have a cluster of 70+ back-end web servers that are
BalancerMember's. If we apachectl stop on a backend web, we are fine.
If however the network dies because of a server crash, arp issues...
whatever, the front-end cache hangs until it comes back. This causes
all of the other back-end web servers web requests to also hang... and
we get a snowball effect that requires a total restart of both the
cache and the back-end webs to clear things up. Obviously this is not
ideal.

This all seems like a TCP timeout issue of some kind. I was perplexed
to discover that doing a netstat -anp|grep [backend that died ip]
Only showed 8 connections in the SYN_SENT state. I also notice that
the Apache balancer-manager scoreboard marks the web server as ERR
(appropriately)... yet we are still hanging on something.

We have eliminated the cluster fs as the culprit, as network issues on
a non-back-end web server do not cause a problem.

We would be perfectly happy if a web server not responding for 5
seconds meant it was marked as an error cluster and it didn't try to
connect for quite some time. So far we have specified each balancer
member to have:
retry=120 max=40

We do this because we have some web pages that can legitimately take
up to 60 seconds to finish rendering. Is there some kind of timeout we
can configure at the OS or apache level that would prevent waiting on
a host that has gone completely dark for 5 seconds?

Thanks in advance for any advice people have.

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