We are using a collection of Squid instances (version 2.7.stable9) as caching proxies behind a single gateway IP, processing requests from a large number of users.
We've observed that a number of websites throttle our usage when requests targeting a given domain are processed by two or more instances. This does not occur when all requests to this domain are processed by a single instance.
We are trying to find the root cause for this behaviour, and the fact that it does not occur with a single Squid instance may help us diagnose. From the origin server's perspective, only two changes are visible between using a single instance and using two or more:
* The value injected in the 'Via' header differs between Squid instances. The web server may not expect requests coming from a single IP to contain different values for the HTTP 'Via' header. This is something we can investigate ourselves, but input would be welcome.
* If each Squid limits the number of connections to a given server, using several instances may cause the origin server to see a number of connections which exceeds what they expect to see from a single IP. This is the question for this forum: does Squid actually limit the number of per-server connections? Is this number configurable (either in squid.conf or by rebuilding)?
Note that each affected website resolves to a single IP; Squid instances are not receiving different IPs from DNS servers.
Francis Fauteux
Software Engineer
Received on Mon Feb 27 2012 - 21:36:17 MST
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