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Value of "Expires" header differ for caching and content serving servers

April 06, 2011 06:47AM
I have a following servers structure:
content.server contains an Apache instance, which processes one simple PHP script. On the same node Nginx is set as a caching proxy to that Apache.
caching.server contains Nginx with proxy_cache directive, with upstream set to content.server

Php script generates an XML file, that has a lifetime of 30 minutes. This is achieved by setting headers in PHP code: "Cache-Control: max-age=1800", "Date: now()" and "Expires: now()+1800seconds".

content.server serves the cached file correctly:
> Date Wed, 06 Apr 2011 09:50:49 GMT
> Cache-Control public, must-revalidate, max-age=1800
> Expires Wed, 06 Apr 2011 10:14:25 GMT
> Etag 26ee7051c360ee28d2a5697fb2b97a03

But approximately half of the time caching.server serves the content where Date header is larger than Expires, and Expires is different from the one on content.server:
> Date Wed, 06 Apr 2011 09:49:58 GMT
> Cache-Control public, must-revalidate, max-age=1800
> Expires Wed, 06 Apr 2011 09:44:23 GMT
> Etag 26ee7051c360ee28d2a5697fb2b97a03


My questions is: what can cause such behaviour, when caching nginx sets its own Expires header?
Subject Author Posted

Value of "Expires" header differ for caching and content serving servers

i.s.ivanov2 April 06, 2011 06:47AM

Re: Value of "Expires" header differ for caching and content serving servers

i.s.ivanov2 April 06, 2011 07:39AM

Re: Value of "Expires" header differ for caching and content serving servers

i.s.ivanov2 April 07, 2011 07:46AM

Re: Value of "Expires" header differ for caching and content serving servers

Maxim Dounin April 07, 2011 08:16AM

Re: Value of "Expires" header differ for caching and content serving servers

Ryan Malayter April 07, 2011 03:56PM

Re: Value of "Expires" header differ for caching and content serving servers

Maxim Dounin April 07, 2011 09:28PM

Re: Value of "Expires" header differ for caching and content serving servers

i.s.ivanov2 April 11, 2011 01:37AM



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