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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.

Ted Wilmont
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1 Answers1

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You should be replace that with

proxy_cache_revalidate on

as it is indicated in Nginx documentation

proxy_cache_revalidate instructs NGINX to use conditional GET requests when refreshing content from the origin servers. If a client requests an item that is cached but expired as defined by the cache control headers, NGINX includes the If-Modified-Since field in the header of the GET request it sends to the origin server. This saves on bandwidth, because the server sends the full item only if it has been modified since the time recorded in the Last-Modified header attached to the file when NGINX originally cached it.

Alfonso S.
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