Hiding 302 replies from clients

Artur Bergman sky at crucially.net
Mon Aug 9 07:13:47 CEST 2010

if(bereq.status == 302) {
	set req.url = bereq.http.Location;

Would this work?

On Aug 8, 2010, at 2:50 PM, Paul Millar wrote:

> Hi all,
> I've a question about whether something is possible with Varnish.
> Suppose the back-end replies with a 302 return code ("Found" or "Moved
> temporarily").  From a quick test, it seems that Varnish will relay  
> this 302
> reply back to the client.  The client will extract the new URL from  
> the
> "Location" header field and make a second request.
> [aside: from a quick test, it seems that varnish always caches the  
> 302 reply
> from the back-end.  It will give the same reply if a client asks for  
> the same
> URL, even when the back-end reply omits any "Cache-Control" or  
> "Expires"
> header.  If this is so then it's a bug.]
> What I'd like to happen is that, when receiving a 302 reply from the  
> back-end,
> Varnish would attempt to fetch the data from the redirect URL (given  
> in the
> "Location" header).  Assuming the data is accessible from this URL  
> then the
> client would obtain the data without being redirected.
> Is it possible to configure varnish to do this?
> In case you're wondering, here's why... Simplifying the setup  
> somewhat,
> consider a distributed http service where a central server that  
> knows about
> all the files but hosts none of the data.  When a client requests a  
> file, the
> central server redirects the client to whichever server is currently  
> hosting
> that file by replying with a 302 reply.  The client can read that  
> file from the
> hosting server with the URL in the "Location" header.
> The redirect URL ("Location" header) is a single-use URL: subsequent  
> attempts
> to use that URL will fail.  Requests from the central server will  
> generate a
> new single-use URL.  Since 302 requests are non-cachable by default  
> and
> conforming clients should make subsequent requests to the central  
> server, this
> works.
> However, it does make caching awkward.  The stored data does not  
> change, so
> could be cached.  However, if the client sees the redirect then the  
> data would
> be cached against the single-use URLs, and subsequent requests for  
> the same
> data wouldn't use the cached copy.
> Cheers,
> Paul.
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