1

I have an Amazon EC2 Web Server instance which serves gzipped content when the Accept-Encoding header is set to gzip. But when I make the same request with the exact same header to a CloudFront CDN with the origin server as my Amazon EC2 instance, it doesn't send back a gzipped response.

I also tried creating a new CloudFront distribution(because I thought that the old distribution might have uncompressed response cached) and then making the same request and I still get an uncompressed response.

Can someone please tell me what I may be missing?

chaudharyp
  • 3,394
  • 3
  • 26
  • 42

1 Answers1

0

This has been marked as a possible duplicate of a question relating to S3. The question is around EC2 - not S3, so I don't think this is a duplicate.

You’re likely seeing this issue due to Cloudfront adding a ‘Via’ header to the requests made to your origin server - it’s a know issue with IIS.

If you were to look at the incoming HTTP requests to your origin, you’d see something like this in your HTTP headers:

Via=1.1 9dc1db658f6cee1429b5ff20764c5b07.cloudfront.net (CloudFront)
X-Amz-Cf-Id=k7rFUA2mss4oJDdT7rA0HyjG_XV__XwBV14juZ8ZAQCrbfOrye438A==
X-Forwarded-For=121.125.239.19, 116.127.54.19

The addition of a ‘Via’ header is standard proxy server behaviour. When IIS sees this, it drops the gzip encryption (I’m guessing due to an assumption that older proxy servers couldn’t handle compressed content).

If you make the following changes to your applicationHost.config, you should rectify the issue:

<location path="Your Site">
  <system.webServer>
    <httpCompression noCompressionForHttp10="false" noCompressionForProxies="false" />
  </system.webServer>
</location>

The other issue to watch out for is that IIS doesn’t always compress the first response it receives for a given resource, therefore, Cloudfront may make a request to the origin, receive, cache and then serve uncompressed version of the content to subsequent visitors. Again you can modify this behaviour using the serverRuntime settings in the applicationHost.config:

<location path="Your Site">
  <system.webServer>
    <httpCompression noCompressionForHttp10="false" noCompressionForProxies="false" />
    <serverRuntime frequentHitThreshold="1" frequentHitTimePeriod="00:00:05"       />
  </system.webServer>

More details on these settings here: http://www.iis.net/configreference/system.webserver/serverruntime http://www.iis.net/configreference/system.webserver/httpcompression

Credit to this blog post for explaining the issue: http://codepolice.net/2012/06/26/problems-with-gzip-when-using-iis-7-5-as-an-origin-server-for-a-cdn/

Mark Kelly
  • 553
  • 4
  • 13
  • The platform in Windows and the server is IIS. The problem is that the server serves gzipped files when the domain name is of the server. But when the domain name is of the Cloudfront CDN, then the file served is not gzipped. Requests to both, the server directly and to CDN, have `Accept-Encoding` header set as `gzip, deflate, sdch` – chaudharyp Jan 31 '15 at 15:53
  • Hi @pa669 - did this fix the issue you were having? – Mark Kelly Feb 02 '15 at 20:15
  • Hi Mark. Sorry, I was out for a while. So didn't try out the solution. Will try and revert back ASAP. Thanks. – chaudharyp Feb 08 '15 at 17:42
  • Hey @mark. Really sorry for the very delayed response. The solution above didn't help. – chaudharyp Apr 15 '15 at 17:47