How to send proxy cache status to backend server?

[Maxim Dounin]

Hello!

On Thu, Mar 27, 2014 at 03:01:22PM +0530, Makailol Charls wrote:

> Hi Maxim,
> 
> Apart from passing cache status to backend, would it be possible to send
> some other headers which are stored in cache?
> 
> For example, If backed sets header "Foo : Bar" , which is stored in cache.
> Now when cache is expired , request will be sent to backend. At that time
> can we send the value of Foo header stored in cache to upstream backend?
> 
> I tried to achieve this with below code but it could not work.
> proxy_set_header Foo  $upstream_http_Foo;
> 
> Would you suggest me how to achieve this or what am I doing wrong here.

This is not something possible.

> 
> Thanks,
> Makailol
> 
> 
> 
> 
> On Thu, Mar 20, 2014 at 6:56 PM, Maxim Dounin <mdounin at mdounin.ru> wrote:
> 
> > Hello!
> >
> > On Thu, Mar 20, 2014 at 09:38:40AM +0530, Makailol Charls wrote:
> >
> > > Hi,
> > >
> > > Is there some way to achieve this? I want to pass requests to backend
> > based
> > > on cache status condition.
> >
> > This is not something easily possible, as cache status is only
> > known after we started processing proxy_pass and already know
> > which backend will be used.  (Note that by default proxy_cache_key
> > uses $proxy_host, which wouldn't be known otherwise.)
> >
> > If you want to check BYPASS as in your previous message, I would
> > recommend checking relevant conditions from proxy_cache_bypass
> > separately.  As a more generic though less effective aproach, an
> > additional proxy layer may be used.
> >
> > --
> > Maxim Dounin
> > http://nginx.org/
> >
> > _______________________________________________
> > nginx mailing list
> > nginx at nginx.org
> > http://mailman.nginx.org/mailman/listinfo/nginx
> >

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-- 
Maxim Dounin
http://nginx.org/