304 Status code for my Azure CDN images hosted in Azure Blob Storage
My images are stored in azure blob storage and referenced through my web application using my azure CDN. However all images return a 304 response header. Ideally I dont want the browser to return to the CDN to check for validity at every request, instead for the browser to always use the cache. - Well for at the life of the image cache.
With my limited knowledge of Caching, I understand that the cache uses the ETag value to compare if the version of the image is the same when requested. In this case it is and the CDN returns a 304 response. But because the CacheControl header is set as public, max-age=2592000 I would hope the browser would use the cached copy of the image. I have another CDN setup that has a hosted service endpoint which returns a 200 response because I remove the ETag value.
Any help with this would be greatly appreciated.
When ETag "triggers" 304 response => the browser has sent If-None-Match validating request to the server. This is normally done after max-age has elapsed. You could find a good description of this here:
https://stackoverflow.com/a/500103/2550808
it is also worth mentioning, Firefox browser settings should be set to default: go to about:config page and check this settings: http://kb.mozillazine.org/Browser.cache.check_doc_frequency
Going back to your question, something might be wrong with Cache-Control header the server returns to the browser. In my modest personal experience I didn't encounter explicitly public version of the header, it would be more likely just this:
Cache-Control: max-age=3600, must-revalidate
Anyway, here is pretty good description of headers pertaining to caching:
https://www.mnot.net/cache_docs/
Alternatively, there might be other reasons for incessant re-validation to consider: