Re: Does squid re-resolve hostnames named in squid.conf?

From: Michael Sparks <>
Date: Wed, 16 Sep 1998 17:31:05 +0000

Bob Franklin <> writes:

> The UK Joint Academic Network (JANET) provides a National Cache which
> individual institutions are supposed to use as their upstream parents.
> To allow them (the National Cache managers) to move institutions around
> between different parent caches in their cache farm, they set up aliases
> for each site to use: '' is one of ours.
> What I'd like to know is, if they change this alias to point at another
> machine, will Squid notice and switch over? Or, does it only resolve the
> hostnames -> IP addresses on startup and we'd need to HUP Squid
> occasionally to have it re-resolve these names?


After some experimentation by creating a name which I can alias to
different IP addresses, I've discovered that squid does *not* detect the
change in the name, neither at the time your cache machine can resolve
(say) nor after a kill -HUP at that time.
Whether squid does re-resolve it or not though perhaps depends on the
DNS entry stating how long the refresh value is? (I have given squid
about 3

If however squid is killed and restarted by RunCache, then squid detects
change in IP (not a big suprise) and uses the correct host. In running
national cache due to memory leaks with squid we automatically monitor
size of the squid process and kill it to relieve memory problems.
Working on
the assumption that most users of the cache probably do the same, when
we make
minor changes to the DNS (mainly due to user request) we don't need to
inform individual site caches.

That said, we are in the process of re-allocating UK institutions sites
on cache size & site usage, since we have recently been working very
hard substantially increasing the total capacity of the national cache
(both in
terms of storage and number of machines) and will be contacting each
individual site shortly.


Local Caching:  National Caching :
Address:  G95C, Communications, Operations and Systems, Manchester
          University of Manchester, Oxford Rd, Manchester, M13 9PL.
Tel:      0161-275 7195    Fax: 0161-275 6040
Received on Wed Sep 16 1998 - 08:32:17 MDT

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