Re: [squid-users] Caching dynamic content, trading between HTTP versions

From: Amos Jeffries <>
Date: Tue, 30 Apr 2013 23:03:48 +1200

On 30/04/2013 10:45 p.m., Andrea Aime wrote:
> Thanks for the prompt reply. Comments inline.
> On Tue, Apr 30, 2013 at 12:21 PM, Amos Jeffries <> wrote:
>>> So basically, we need the cache to talk HTTP 1.1 with the webapp.
>> Both If-Modified-Since and If-None-Modified are optional features. There is
>> no requirement in HTTP for any of the client, gateway or server to use
>> either of them.
> Yes, that was my understanding as well. However, I thought major browsers
> support them, and assumed (wrongly it seems) that Squid would also support them.
> By your mail it seems Squid does not support validation towards the dynamic
> webapp via If-None-Modified.
> Out of curiosity, does it support If-Modified-Since instead?

This all depends on your definition of "support"...

Squid will accept If-None-Match from clients and validate cached content
using it, as well as passing it on if necessary to upstream servers.
What Squid is missing is _generating_ the header if it is not supplied
by the client.

Yes Squid supports both client-supplied and Squid-generated
If-Modified-Since headers.

>>> So far so good. Now enter a second level of caching, a CDN made with
>>> cloudfront,
>>> and here is the gotcha: cloudfront only supports HTTP 1.0 requests towards
>>> the
>>> origin, which in this case would be Squid.
>> That is unfortunate. A missing feature in CloudFront. Even more
>> unfortunately it coincides with Squid missing the same feature ...
> Unfortunately CloudFront is not open source, so nothing I can do about it:
> (besides eventually looking into another CDN solution)

I'm a litte surprised to hear that they are omitting If-None-Match, I
would have expected that they at least pass on the browser supplied
headers like Squid does. That is trivial to support and has good
benefits for caching.

>>> Any other suggestion about how this could be handled?
>> Adding the If-None-Modified feature to either CloudFront or Squid is

Arg. Sorry. I meant If-None-Match there.

>> probably a good solution. I believe have a project
>> underway to add it to Squid. You may want to contact Alex there about
>> getting access or sponsoring further progress.
> Thanks for letting me know.
> However, would it do me any good if CloudFront does not support
> If-None-Modified?

... and yes it sounds like exactly what you need.

Received on Tue Apr 30 2013 - 11:03:55 MDT

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