Thanks for the reply Peter.
I've noticed something interesting and wondered if you could shed some
light on it.
Simply adding:
proxy_ignore_headers Cache-Control Expires;
Enables 304 responses from the origin server without setting:
proxy_set_header If-Modified-Since $http_if_modified_since;
I'm confused.
On 26/07/2017 09:11, Peter Booth wrote:
I can’t see an obvious issue, but I can say that there is no such
thing as a simple web server setup where caching is involved.
I have gray hairs that appeared after working with a high traffic
retail website that had seven levels of caching
(browser cache, CDN, hardware load balancer, nginx reverse proxy,
servlets that write content, tangosol /oracle coherence, endeca caching)
I’m hoping that you are living in a saner world than that one but I’m
sure that you will have some craziness.
I would encourage you to add $upstream_cache_status to your log format
and/or add the directive add_headerX-Cache-Status $upstream_cache_status;
Instrumenting the cache can be a real life-saver when things go awry.
I’d also strongly encourage you to use redbot.org <http://redbot.org>
to check for aberrant behavior and webpagetest.org
<http://webpagetest.org>
to see how different browsers handle your site.
Peter
On Jul 26, 2017, at 3:29 AM, Ryan Barclay <[email protected]
<mailto:[email protected]>> wrote:
The following config seems to work for the situation I discussed:
proxy_cache_valid 200 3M;
proxy_cache_valid 304 0;
proxy_cache_revalidate on;
proxy_set_header If-Modified-Since $http_if_modified_since;
proxy_ignore_headers Cache-Control Expires;
... can anybody see any problems with this config or future problems
that may arise?
On 24/07/2017 16:20, Ryan Barclay wrote:
We have a pretty simple setup with NGINX sitting on the front and a
backend server (on a separate physical server) that provides the
content.
Nginx then caches content based on the EXPIRES and Cache-Control
headers set by the origin server.
We noticed that NGINX was not issuing 304 headers to images that
were not in the local NGINX cache when the If-Modified-Since header
was sent by the client. Instead, it would issue a 200 with the full
data file.
To fix this, we applied:
proxy_set_header If-Modified-Since $http_if_modified_since
So then the If-Modified-Since header was passed to the backend and
of course, it returned correctly with the 304 header - great.
But what we noticed was that NGINX would cache this 304 response and
deliver future responses as 304 to clients even without the
If-Modified-Since header.
How can we disable caching of 304 responses and fix this issue?
Thank you for your help, suggestions, and tips in advance.
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