<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">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.</div><div class="">I have gray hairs that appeared after working with a high traffic retail website that had seven levels of caching</div><div class="">(browser cache, CDN, hardware load balancer, nginx reverse proxy, servlets that write content, tangosol /oracle coherence, endeca caching)</div><div class=""><br class=""></div><div class="">I’m hoping that you are living in a saner world than that one but I’m sure that you will have some craziness. </div><div class="">I would encourage you to add <span style="font-family: Consolas, 'Andale Mono', 'DejaVu Sans Mono', monospace; font-size: 10.199999809265137px; orphans: 2; white-space: pre-wrap; widows: 2; background-color: rgb(238, 238, 238);" class="">$upstream_cache_status</span> to your log format</div><div class="">and/or add the directive <span style="font-family: inherit; font-style: inherit; orphans: 2; white-space: pre-wrap; widows: 2; box-sizing: inherit; border: 0px; font-size: 12.75px; font-weight: 700; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" class="">add_header</span><span style="font-family: Consolas, 'Andale Mono', 'DejaVu Sans Mono', monospace; font-size: 0.85em; font-style: inherit; orphans: 2; white-space: pre-wrap; widows: 2; background-color: rgb(238, 238, 238);" class=""> X-Cache-Status $upstream_cache_status;</span></div><div class="">Instrumenting the cache can be a real life-saver when things go awry.</div><div class=""><br class=""></div><div class="">I’d also strongly encourage you to use <a href="http://redbot.org" class="">redbot.org</a> to check for aberrant behavior and <a href="http://webpagetest.org" class="">webpagetest.org</a></div><div class="">to see how different browsers handle your site. </div><div class=""><br class=""></div><div class="">Peter</div><div class=""><br class=""></div><div class=""><br class=""></div><br class=""><div><blockquote type="cite" class=""><div class="">On Jul 26, 2017, at 3:29 AM, Ryan Barclay <<a href="mailto:ryan@rbftpnetworks.com" class="">ryan@rbftpnetworks.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">The following config seems to work for the situation I discussed:<br class=""><br class="">proxy_cache_valid 200 3M;<br class="">proxy_cache_valid 304 0;<br class="">proxy_cache_revalidate on;<br class="">proxy_set_header If-Modified-Since $http_if_modified_since;<br class="">proxy_ignore_headers Cache-Control Expires;<br class=""><br class=""><br class="">... can anybody see any problems with this config or future problems that may arise?<br class=""><br class=""> <br class="">On 24/07/2017 16:20, Ryan Barclay wrote:<br class=""><blockquote type="cite" class="">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.<br class=""><br class="">Nginx then caches content based on the EXPIRES and Cache-Control headers set by the origin server.<br class=""><br class="">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.<br class=""><br class="">To fix this, we applied:<br class="">proxy_set_header If-Modified-Since $http_if_modified_since<br class=""><br class="">So then the If-Modified-Since header was passed to the backend and of course, it returned correctly with the 304 header - great.<br class=""><br class="">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.<br class=""><br class="">How can we disable caching of 304 responses and fix this issue?<br class=""><br class="">Thank you for your help, suggestions, and tips in advance.<br class=""></blockquote><br class="">_______________________________________________<br class="">nginx mailing list<br class=""><a href="mailto:nginx@nginx.org" class="">nginx@nginx.org</a><br class="">http://mailman.nginx.org/mailman/listinfo/nginx<br class=""></div></div></blockquote></div><br class=""></body></html>