Image not stored in cache even though headers are set - html

Question

The last few hours, I have tried to figure out, why the following image is not cached in the browser, after it is requested the first time:
http://runrpg.net/assets/images/screenshots/placeit_outdoor_wide.jpg
I understand that the correct headers have to be set, and currently the response header looks like this:
HTTP/1.1 200 OK
Date: Sat, 04 Jan 2014 16:35:53 GMT
Server: Apache/2.4.4 (Unix) OpenSSL/1.0.1e PHP/5.5.3 mod_perl/2.0.8-dev
Perl/v5.16.3
Last-Modified: Sat, 30 Nov 2013 01:37:52 GMT
ETag: "1dac5-4ec5afebf3c00-gzip"
Accept-Ranges: bytes
Cache-Control: max-age=2592000
Expires: Mon, 03 Feb 2014 16:35:53 GMT
Vary: Accept-Encoding
Content-Encoding: gzip
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: image/jpeg
As you can see, the "Expires" header is set to "Mon, 03 Feb 2014 16:35:53 GMT" and I also included a "Cache-Control: max-age=2592000".
Can you help me and tell me what I am missing?
Your help would be very much appreciated.
Thanks!

Answer 1

This is most likely due to your server not validating ETags correctly. While cache validation through the Last-Modified header works perfectly:
$ HEAD -H "If-Modified-Since: Sat, 30 Nov 2013 01:37:52 GMT" http://runrpg.net/assets/images/screenshots/placeit_outdoor_wide.jpg
304 Not Modified
Cache-Control: max-age=290304000, public
Connection: close
Date: Sat, 04 Jan 2014 19:01:30 GMT
ETag: "1dac5-4ec5afebf3c00"
Server: Apache/2.4.4 (Unix) OpenSSL/1.0.1e PHP/5.5.3 mod_perl/2.0.8-dev Perl/v5.16.3
Expires: Thu, 09 Jan 2014 19:01:30 GMT
Client-Date: Sat, 04 Jan 2014 19:01:30 GMT
Client-Peer: 80.70.3.110:80
Client-Response-Num: 1
The same cannot be said with ETags:
$ HEAD -H 'If-None-Match: "1dac5-4ec5afebf3c00-gzip"' http://runrpg.net/assets/images/screenshots/placeit_outdoor_wide.jpg
200 OK
Cache-Control: max-age=290304000, public
Connection: close
Date: Sat, 04 Jan 2014 19:02:24 GMT
Accept-Ranges: bytes
ETag: "1dac5-4ec5afebf3c00"
Server: Apache/2.4.4 (Unix) OpenSSL/1.0.1e PHP/5.5.3 mod_perl/2.0.8-dev Perl/v5.16.3
Vary: Accept-Encoding
Content-Length: 121541
Content-Type: image/jpeg
Expires: Thu, 09 Jan 2014 19:02:24 GMT
Last-Modified: Sat, 30 Nov 2013 01:37:52 GMT
Access-Control-Allow-Credentials: true
Access-Control-Allow-Headers: origin, x-requested-with, content-type, X-Titanium-Id
Access-Control-Allow-Methods: PUT, GET, POST, DELETE, OPTIONS
Access-Control-Allow-Origin: http://127.0.0.1:8020
Client-Date: Sat, 04 Jan 2014 19:02:24 GMT
Client-Peer: 80.70.3.110:80
Client-Response-Num: 1
Bottom line: The problem is your server, not any clients. This seems to be a known issue with Apache 2.4.x. A quick solution to this is by switching ETags off:
FileETag None