[squid-users] CARP Failover behavior - multiple parents chosen for URL

Hi,

I've noticed a behavior in CARP failover (on 2.7) that I was wondering
if someone could explain.

In my test environment, I have a non-caching squid configured with
multiple CARP parent caches - two servers, three per box (listening on
ports 1080/1081/1082, respectively, for a total of six servers.

When I fail a squid instance and immediately afterwards run GETs to
URLs that were previously directed to that instance, I notice that the
request goes to a different squid, as expected, and I see the
following in the log for each request:

May 6 11:43:28 cdce-den002-001 squid[1557]: TCP connection to http-
cache-1c.den002 (http-cache-1c.den002:1082) failed

And I notice that the request is being forwarded to a different, but
consistent, parent.

After ten of the above requests, I see this:

May 6 11:43:41 cdce-den002-001.den002 squid[1557]: Detected DEAD
Parent: http-cache-1c.den002

So, I'm presuming that after ten failed requests, the peer is
considered DEAD. So far, so good.

The problem is this: During my test GETs, I noticed that immediately
after the "Detected DEAD Parent" message was generated, the parent
server that the request was being forwarded to changed - as if there's
an "interim" decision made until the peer is officially declared DEAD,
and then another hash decision made afterwards. So while consistent
afterwards, it's apparent that during the failover, the parent server
for the test URL changed twice, not once.

Can someone explain this behavior?

Thanks,

-C
Received on Wed May 06 2009 - 17:52:46 MDT