Running multiple instances of Squid on a system

Running multiple instances of Squid on a system is not hard, but it requires the administrator to make sure they don't stomp on each other's feet, and know how to recognize each other to avoid forwarding loops (or misdetected forwarding loops).

Relevant squid.conf directives

• visible_hostname

  • you may want to keep this unique for troubleshooting purposes

• unique_hostname

  • if you don't change the visible_hostname and want your caches to cooperate, at least change this setting to properly detect forwarding loops

• http_port

  • either the various squids run on different ports, or on different IP addresses. In the latter case the syntax to be used is 1.2.3.4:3128 and 1.2.3.5:3128

• icp_port, snmp_port

  • same as with http_port. If you don need ICP and SNMP, just disable them by setting them to 0.

• cache_access_log, cache_log

  • you want to have different logfiles for you different squid instances. Squid might even work when all log to the same files, but the result would probably be a garbled mess

• pid_filename

  • this file must be changed. It is used by squid to detect a running instance and to send various internal messages (i.e. squid -k reconfigure)

• cache_dir

  • make sure that no overlapping cache_dirs exist. Squids do not coordinate when accessing them, and shuffling stuff around each others' playground is a bad thing ^TM

Tips

The easiest way I found to manage multiple squids runnning on one single box was to:

• create a configuration file per instance

• write a small shell script (named squid-something) per instance, containing:

exec /usr/local/sbin/squid -f /usr/local/etc/squid-something.conf $@

(of course, relevant path changes may have to be applied).

And then just run them as you would with a single-install squid setup.