Conditional backend requests (ETag)

[Guillaume Quintard]

Hi Magnus,

The documention you are looking for is here :
https://www.varnish-cache.org/docs/4.0/reference/vcl.html

And beresp.keep is definitely what you are looking for. If ttl is expired
but not ttl + keep, varnish will issue a conditionnal request.

-- 
Guillaume Quintard

On Fri, Sep 18, 2015 at 12:35 PM, Magnus Hoff <maghoff at gmail.com> wrote:

> Hi :)
>
> What is the status of support for conditional backend requests?
>
> My use case is accelerating CouchDB, which has good support for ETags,
> but offers no other caching opportunities.
>
> I have found [1] which leads me to think that the branch implementing
> this feature was merged to trunk in 2011. According to [2] (which also
> says, in big bold letters, "This documentation is out of date"), I
> should be able to see this working with the default VCL: "In the
> default case (i.e. if not superseded by something in VCL), a
> conditional request is generated during fetch with If-Modified-Since
> and/or If-None-Match headers whose values are taken from stale_obj's
> Last-Modified and/or ETag headers."
>
> [1]:
> https://www.varnish-cache.org/lists/pipermail/varnish-commit/2011-July/006720.html
> [2]: https://www.varnish-cache.org/trac/wiki/BackendConditionalRequests
>
> However, when testing with the latest Varnish from the Varnish Ubuntu
> repository (https://www.varnish-cache.org/installation/ubuntu),
> "varnish-4.0.3 revision b8c4a34", I am unable to trigger conditional
> backend requests in the default configuration. I have feebly tried
> making the VCL more explicit in that it should try to keep the ETagged
> versions around by setting beresp.keep explicitly, but I can't seem to
> effect a change in behavior.
>
> So, what is happening? Does Varnish currently support what I am
> looking for? What is the up to date documentation on this? Is there
> support for this on a branch still? How is that branch coming along?
>
>
> Thank you :)
> - Magnus Hoff
>
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