Conditional GET (was Re: caching using ETags to vary the content)

Ricardo Newbery ric at
Wed Nov 12 12:19:10 CET 2008

On Nov 4, 2008, at 2:19 PM, Miles wrote:

> Ryan Tomayko wrote:
>> On 11/4/08 12:51 PM, Miles wrote:
>>> I know varnish doesn't do If-None-Match, but I don't think that is a
>>> problem in this scheme.
>> I'm curious to understand why Varnish doesn't do validation /  
>> conditional GET.
>> Has If-Modified-Since/If-None-Match support been considered and  
>> rejected on
>> merit or is it something that could theoretically be accepted into  
>> the
>> project? Has it just not received any real interest?
>> Personally, I'd love to see support for conditional GET as this can
>> significantly reduce backend resource use when the backend  
>> generates cache
>> validators upfront and 304's without generating the full response.
>> Ryan
> AFAIK varnish does do if-modified-since, just not if-none-match
> Miles

Unless this has changed with 2.0, varnish will *respond* to if- 
modified-since (IMS) with a 304 response if there is cached entry that  
fails this condition, but varnish will neither *pass* the IMS header  
to the backend (unless you customize the vcl) nor *generate* an IMS to  
the backend.


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