<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>Ryan,</div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature">Just to be pedantic, can you spell out exactly what you meant when you said "<span style="background-color: rgba(255, 255, 255, 0);">and deliver future responses as 304 to clients even without the If-Modified-Since header?"</span></div><div id="AppleMailSignature">What requests were triggering the 304 response?</div><div id="AppleMailSignature">Were you observing what a browser was seeing or were you using curl or wget to trigger the response?</div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature">Peter<br><br>Sent from my iPhone</div><div><br>On Jul 26, 2017, at 5:10 AM, Ryan Barclay <<a href="mailto:ryan@rbftpnetworks.com">ryan@rbftpnetworks.com</a>> wrote:<br><br></div><blockquote type="cite"><div>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<p>So this config seems to work:</p>
<p>proxy_cache_valid 200 3M;<br>
proxy_cache_valid 304 0;<br>
proxy_cache_valid 404 0;<br>
proxy_cache_revalidate on;<br>
proxy_ignore_headers Cache-Control Expires;</p>
<p><br>
</p>
<p>There is no need for: <br>
</p>
<p>proxy_set_header If-Modified-Since $http_if_modified_since;</p>
<p><br>
</p>
<p><br>
</p>
<pre class="moz-signature" cols="72"></pre>
<div class="moz-cite-prefix">On 26/07/2017 09:57, Ryan Barclay
wrote:<br>
</div>
<blockquote type="cite" cite="mid:6913bf6b-aaee-885a-41b1-a386ea788e34@rbftpnetworks.com">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<p>Thanks for the reply Peter.</p>
<p>I've noticed something interesting and wondered if you could
shed some light on it.</p>
<p>Simply adding:<br>
</p>
<p>proxy_ignore_headers Cache-Control Expires;</p>
<p>Enables 304 responses from the origin server without setting:</p>
<p>proxy_set_header If-Modified-Since $http_if_modified_since;</p>
<p>I'm confused.<br>
</p>
<div class="moz-cite-prefix">On 26/07/2017 09:11, Peter Booth
wrote:<br>
</div>
<blockquote type="cite" cite="mid:63438CEF-8E36-4496-A069-1A51F33F0C24@me.com">
<meta http-equiv="Content-Type" content="text/html;
charset=utf-8">
<div class="">I can’t see an obvious issue, but I can say that
there is no such thing as a simple web server setup where
caching is involved.</div>
<div class="">I have gray hairs that appeared after working with
a high traffic retail website that had seven levels of caching</div>
<div class="">(browser cache, CDN, hardware load balancer, nginx
reverse proxy, servlets that write content, tangosol /oracle
coherence, endeca caching)</div>
<div class=""><br class="">
</div>
<div class="">I’m hoping that you are living in a saner world
than that one but I’m sure that you will have some craziness. </div>
<div class="">I would encourage you to add <span style="font-family: Consolas, 'Andale Mono', 'DejaVu Sans Mono', monospace; font-size: 10.199999809265137px; orphans: 2; white-space: pre-wrap; widows: 2; background-color: rgb(238, 238, 238);" class="">$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="" moz-do-not-send="true">redbot.org</a>
to check for aberrant behavior and <a href="http://webpagetest.org" class="" moz-do-not-send="true">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="" moz-do-not-send="true">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="">
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</div>
</blockquote>
</div>
<br class="">
<br>
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</blockquote>
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