Order of HTTP headers change cache behaviour
mdounin at mdounin.ru
Wed Feb 22 16:28:28 UTC 2012
On Wed, Feb 22, 2012 at 05:05:32PM +0100, Simone Fumagalli wrote:
> Looking at my log I've noticed that some pages were not cached. After a bit of debugging I've noticed that the order in which the HTTP header are returned from Apache change how NGINX this save the page in the cache
> So a page with this code is *NOT* cached
> header('Content-Type: text/html; charset=UTF-8');
> header('Last-Modified: Wed, 22 Feb 2012 14:44:11 GMT');
> header('Expires: Wed, 11 Jan 1984 05:00:00 GMT');
> header("X-Accel-Expires: 600");
> header('Cache-Control: no-cache, must-revalidate, max-age=0');
> header('Pragma: no-cache');
> Echo "Hello World !";
> if I comment/delete the line header('Expires: Wed, 11 Jan 1984 05:00:00 GMT'); the page is cached.
> Even if I move header("X-Accel-Expires: 600") before header('Expires: Wed, 11 Jan 1984 05:00:00 GMT'); the page is cached
> Same thing happen for the header Cache-Control. If is before X-Accel-Expires the page is not cached if is after it is !
> The conf for NGINX is very standard and proxy_cache_valid is not specified.
> Is this correct ? Where am I wrong ?
This probably should be counted as a bug (or at least
Here are what happens: if the Expires header comes first, it
disables caching due to being set to date in the past. The
X-Accel-Expires header which comes later can't re-enable caching.
On the other hand, if X-Accel-Expires comes first, it will set
cache expiration time. The Expires and Cache-Control headers
later will be just ignored as cache expiration time is already
As a workaround you may want to always sent X-Accel-Expires first,
or explicitly ignore other headers with proxy_ignore_headers.
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