MISS from Cloudfront after HIT from Cloudfront

Question

I am switching to Amazon Cloudfront for serving images on my website. To reduce load when we finally make it live, I thought of warming up the cache by hitting image URLs (I am making these request from India and expect majority of users to request from the same region so no need to have a copy of object on all edge locations worldwide).

The problem is that script uses curl to request image and when I access the same URL in browser I get MISS from Cloudfront. So Cloudfront is making two copies of object for these two request.

My current Cloudfront configuration forwards Content-Type request Header to origin.

How should I configure Cloudfront so that it doesn't care about request headers at all and once I made a request (whether curl or using browser) it should serve all future request for same resource from edge and not origin.

Request/Response headers- I am afraid that the Cloudfront url won't be accessible from outside (until we go live) but I am posting request/response headers, this should give you fair idea. Also you can check out caching headers at origin - https://origin.ixigo.com/image/upload/t_thumb,f_auto/r7y6ykuajvlumkp4lk2a.jpg

Response after two successive request using browser
Remote Address:54.230.156.66:443
Request URL:https://youcannotaccess.com/image/upload/t_thumb,f_auto/r7y6ykuajvlumkp4lk2a.jpg
Request Method:GET
Status Code:200 OK
Response Headers
view source
Accept-Ranges:bytes
Age:23
Cache-Control:public, max-age=31557600
Connection:keep-alive
Content-Length:8708
Content-Type:image/jpg
Date:Fri, 27 Nov 2015 09:16:03 GMT
ETag:"-170562206"
Last-Modified:Sun, 29 Jun 2014 03:44:59 GMT
Vary:Accept-Encoding
Via:1.1 7968275877e438c758292828c0593684.cloudfront.net (CloudFront)
X-Amz-Cf-Id:fcbGLv8uBOP89qfR52OWa-NlqWkEREJPpZpy9ix0jdq8-a4oTx7lNw==
X-Backend:image6_40
X-Cache:Hit from cloudfront
X-Cache-Hits:0
X-Device:pc
X-DeviceType:pc
X-Powered-By:xyz

Now same url requested using curl but gave me miss
curl manu-mdc:cache manuc$ curl -I https://youcannotaccess.com/image/upload/t_thumb,f_auto/r7y6ykuajvlumkp4lk2a.jpg
HTTP/1.1 200 OK
Content-Type: image/jpg
Content-Length: 8708
Connection: keep-alive
Age: 0
Cache-Control: public, max-age=31557600
Date: Fri, 27 Nov 2015 09:16:47 GMT
ETag: "-170562206"
Last-Modified: Sun, 29 Jun 2014 03:44:59 GMT
X-Backend: image6_40
X-Cache-Hits: 0
X-Device: pc
X-DeviceType: pc
X-Powered-By: xyz
Vary: Accept-Encoding
X-Cache: Miss from cloudfront
Via: 1.1 4d42171c56a4c8b5c627040e6aa0938d.cloudfront.net (CloudFront)
X-Amz-Cf-Id: fY0LXhp7NlqB-I8F5-1TIMnA6bONjPD3CEp7dsyVdykP-7N2mbffvw==

Now this will give HIT
manu-mdc:cache manuc$ curl -I https://youcannotaccess.com/image/upload/t_thumb,f_auto/r7y6ykuajvlumkp4lk2a.jpg
HTTP/1.1 200 OK
Content-Type: image/jpg
Content-Length: 8708
Connection: keep-alive
Cache-Control: public, max-age=31557600
Date: Fri, 27 Nov 2015 09:16:47 GMT
ETag: "-170562206"
Last-Modified: Sun, 29 Jun 2014 03:44:59 GMT
X-Backend: image6_40
X-Cache-Hits: 0
X-Device: pc
X-DeviceType: pc
X-Powered-By: xyz
Age: 3
Vary: Accept-Encoding
X-Cache: Hit from cloudfront
Via: 1.1 6877899d48ba844a34ea4378ce336f06.cloudfront.net (CloudFront)
X-Amz-Cf-Id: qpPhbLX_5t2Xj0XZuZdjWD2w-BI80DUVyL496meQkLfSEn3ikt7hNg==

Solution

This is similar to this issue: Why are two requests with different clients from the same computer cache misses on cloudfront?

Depending on whether you provide the "Accept-Encoding: gzip" header or not, CloudFront edge server caches the object separately. Since browsers provides this header by default, and your site is likely to be accessed majorly via browser, I will suggest changing your curl call to include this header.

I was facing the same problem, after making the change in my curl call, I started to get a Hit from the browser on my first try via browser (after making a curl call).

Another thing I noticed is that CloudFront requires the full requested object to be downloaded before it will be cached. If you try to download the file partially by specifying the byte range in the curl, the intended object does not get cached, only the downloaded part gets cached as a different object. Same goes for a curl that was terminated in between. The other options I tried were wget call with spider option, but that internally does a HEAD call only and thus does not get the content cached on the edge server.