[Varnish] #477: Change defaults to respect Cache-Control: private

[Varnish]

#477: Change defaults to respect Cache-Control: private
----------------------+-----------------------------------------------------
 Reporter:  olau      |       Owner:  sky            
     Type:  defect    |      Status:  new            
 Priority:  normal    |   Milestone:  Varnish 3.0 dev
Component:  varnishd  |     Version:  trunk          
 Severity:  normal    |    Keywords:                 
----------------------+-----------------------------------------------------
Changes (by kristian):

  * component:  build => varnishd
  * milestone:  => Varnish 3.0 dev


Old description:

> In some cases you'd want to bypass the cache if the web app behind is
> doing something based on the actual connection/request, e.g. inspecting
> the IP address to guestimate the country and then redirecting based on
> that.
>
> In this case, it makes sense to turn off any caches between the web app
> and the browser, but still allow the browser to cache the reply. As I
> read RFC2616, this is what Cache-Control: private is meant for.
>
> Thus I believe the default configuration of Varnish should take Cache-
> Control: private as a hint that the object is not cacheable and let it
> pass. As it is now, default Varnish will share the response between users
> which breaks the web app (this is not just theory, it actually broke mine
> :-).
>
> We talked about it on the mailing list here
>
> http://projects.linpro.no/pipermail/varnish-
> misc/2009-February/002575.html
>
> The only ill effect I can see of it is if you have a really broken
> backend that sends out Cache-Control: private even if it doesn't really
> mean it. But still defaulting to no caching is the safe choice. You can
> always configure Varnish to disregard the header if you know it's fine in
> your case.

New description:

 In some cases you'd want to bypass the cache if the web app behind is
 doing something based on the actual connection/request, e.g. inspecting
 the IP address to guestimate the country and then redirecting based on
 that.

 In this case, it makes sense to turn off any caches between the web app
 and the browser, but still allow the browser to cache the reply. As I read
 RFC2616, this is what Cache-Control: private is meant for.

 Thus I believe the default configuration of Varnish should take Cache-
 Control: private as a hint that the object is not cacheable and let it
 pass. As it is now, default Varnish will share the response between users
 which breaks the web app (this is not just theory, it actually broke mine
 :-).

 We talked about it on the mailing list here

 http://projects.linpro.no/pipermail/varnish-misc/2009-February/002575.html

 The only ill effect I can see of it is if you have a really broken backend
 that sends out Cache-Control: private even if it doesn't really mean it.
 But still defaulting to no caching is the safe choice. You can always
 configure Varnish to disregard the header if you know it's fine in your
 case.

--

Comment:

 Some discussion ensued... regarding http-bis and others. No clear
 conclusion yet, but we should resolve this one way or an other before 3.0.

-- 
Ticket URL: <http://varnish-cache.org/trac/ticket/477#comment:2>
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