Re: [squid-users] Question about reverse proxy and Apache Expires headers

> Matus UHLAR - fantomas wrote:
> >you set up images to expire after a month, and wonder that they don't
> >expire
> >before a month?

On 21.12.08 09:33, Tom Williams wrote:
> As strange as that sounds, basically yes. :) The reason I set the
> expiration period for one month is I don't expect the images to change
> frequently at all. However, if the image DOES change at some point
> within that month time period, I would want the image to be refreshed.

Don't send Expires then. Expires means that the object will NOT be
re-fetched. I think using "Cache-Control: must-revalidate" header should be
enough.

> I'm sure my understanding of this is wrong but I was thinking if I set
> the images to expire after say one day or one week, Squid would purge
> the image that was in the cache and request an updated copy of the
> image.
> If the image isn't changing with much frequency, I wouldn't want
> Squid to fetch a "fresh", yet unchanged, copy of the image with much
> frequency. Since I set the expiration to be since the image was last
> modified, I was thinking Squid would ask the server if the image had
> changed and fetch a new copy if it did. If the image had not changed,
> after a month it would purge the old image and fetch a new one. Now
> that I've written that, that doesn't make much sense either.
>
> So, how do the expires headers impact Squid's interaction with the web
> server in a reverse proxy configuration?

I think you should read RFC2616 (HTTP/1.1) for description of Expires and
Cache-Control headers. They together can be used to fine-tune caching
behaviour on caching proxy servers. The Expires: header just does not what
you want.

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