Re: [squid-users] How to configure squid so it serves stale web pages when Internet Down

 On Tue, 22 Nov 2011 11:57:15 -0500, Doug Karl wrote:
> We are trying to configure Squid for installation in school labs in
> Belize, Central America where the Internet routinely goes down for
> several minutes and sometimes an hour at a time. We are very happy
> to
> serve up stales pages to the children for their classroom session. So
> we need to either: (1) Configure squid to handle such situations
> where
> cached pages are simply served stale when the Internet is down (i.e.
> don't have Internet to verify freshness) or (2) Have squid respond to
> a script that detects the Internet to be down telling it to serve up
> stales pages when Internet down. As configured, our Squid
> implementation will not serve stale pages because it tries to access
> the original Web site and the cached pages are not served up at all.
>
> NOTE: We have tried "Squid Off-line mode" and that does not work as
> you would think as several others reported. SO ARE THERE config
> parameters that can make caching work in the presence of bad Internet
> connection?

 Yes and no.

 The key directive _is_ offline_mode. Although the confusing bit is that
 the mode must be always set to ON for situations like yours. Don't
 toggle it on/off. All it does is expand the type of things Squid caches
 to include some which would normally be discarded immediately. It
 prepares the cache content as best as possible for the second
 directive...

 max_stale - once items already in cache (via offline_mode), this
 controls how long they may be served for after the Internet connection
 starts failing.
   Also there are refresh_pattern max-stale=N options in Squid 2.7 and
 3.2 to provide per-URL staleness control.
   Also HTTP responses from websites can contain max-stale controls
 telling your Squid its safe to cache and serve while stale.

 Note that all of this is determined by the cacheability of the site
 objects from the start. If an object is not safe to cache and re-use the
 page which depends on it will break in some way while offline. A lot of
 sites webmasters do not send cache friendly header and so create sites
 which break very easily.

 Amos
Received on Tue Nov 22 2011 - 21:36:12 MST