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I have a Rails app that uses Cloudfront as its CDN and sprockets to compress assets and set long Cache-Control headers.
First request to an assets gives me response headers like so:
Cache-Control:public, max-age=31536000 Connection:close Content-Encoding:gzip Content-Type:application/javascript Etag:"892a3afb514e3c84646835f9ef101026" Last-Modified:Tue, 17 Jan 2012 16:05:17 GMT Server:thin 1.2.11 codename Bat-Shit Crazy Vary:Accept-Encoding Via:1.0 c662f4e5a3bc7b224ce1bbecb0a23d82.cloudfront.net:11180 (CloudFront), 1.0 fc4797024fafe16fcc03e892c23f078d.cloudfront.net:11180 (CloudFront) X-Amz-Cf-Id:bd2a89fb81bba2513f30d6940347693ef483defb4783da06d81b002af23545c39b9176b2c7cb144f,VF69FYlYU8ezzHQp7QkU2GvEQ8NmDqEwRX-wu7H63yNqE1ZlTaAq3g== X-Cache:Miss from cloudfront X-Runtime:0.012413 X-Ua-Compatible:IE=Edge,chrome=1
Perfect. It missed the cache from Cloudfront, fetched it from my app, so it should load it from there now from now on.
Now... if I refresh the page I get these response headers:
Connection:keep-alive Server:thin 1.2.11 codename Bat-Shit Crazy Via:1.0 86123d99569c9296c8605243e9a10621.cloudfront.net:11180 (CloudFront), 1.0 de9fc23d505dae3d19973a98bfa1eba0.cloudfront.net:11180 (CloudFront) X-Amz-Cf-Id:a7bf6ffb30c43d306835190d210aeb8ec794c1ff619ad7aaecbad220c1822fe165bda624ae8382e1,bcij_88KOAvLPSqEKDRSvOBjEj7atiKBCAjSbqc2cfdb-BHOTi--LA== X-Cache:RefreshHit from cloudfront X-Runtime:0.006909 X-Ua-Compatible:IE=Edge,chrome=1
Looks like it hit Cloudfront. I get a 304 not modified. So it would seem that I'm not downloading the file again HOWEVER, I see this request also being made to my source server.
Why does this happen? Shouldn't Cloudfront always cache my assets now? I'm versioning my assets, so I really NEVER want this to be fetched from the server save for the first request. Is there any way I can force this type of behaviour?
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On your custom origin web server application, add Cache-Control no-cache, no-store, or private directives to the objects that you don't want CloudFront to cache. Or, add Expires directives to the objects that you don't want CloudFront to cache.
Amazon CloudFront scales automatically as globally-distributed clients download software updates. You can make your software available right at the edge where your users are, via the content delivery network.
RefreshHit from cloudfront : This means that CloudFront is still caching but it's making conditional GET with origin to know if the object has been modified or not, if it receives 304 not modified, it serves it from it's cache otherwise the origin would return a new object (in case if object has been modified).
Turns out Cloudfront won't respect the Cache-Control header if no Date header is set.
Adding in a date header to the assets fixed everything.
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