How to enable gzip HTTP compression on Windows Azure dynamic content

Well it took a very long time ... but I have finally solved this, and I want to post the answer for anyone else who is struggling. The solution is very simple and I've verified that it does definitely work!!

Edit your ServiceDefinition.csdef file to contain this in the WebRole tag:

    <Startup>      <Task commandLine="EnableCompression.cmd" executionContext="elevated" taskType="simple"></Task>    </Startup>

In your web-role, create a text file and save it as "EnableCompression.cmd"

EnableCompression.cmd should contain this:

%windir%\system32\inetsrv\appcmd set config /section:urlCompression /doDynamicCompression:True /commit:apphost%windir%\system32\inetsrv\appcmd set config  -section:system.webServer/httpCompression /+"dynamicTypes.[mimeType='application/json; charset=utf-8',enabled='True']" /commit:apphost

.. and that's it! Done! This enables dynamic compression for the json returned by the web-role, which I think I read somewhere has a rather odd mime type, so make sure you copy the code exactly.

Well at least I'm not alone on this one - and it's still a stupid PITA almost a year later.

The problem is a MIME type mismatch. WCF returns JSON response with Content-Type: application/json; charset=UTF-8. The default IIS configuration, about halfway down that page, does not include that as a compressible MIME type.

Now, it might be tempting to add an <httpCompression> section to your web.config, and add application/json to that. But that's just a bad way to waste a good hour or two - you can only change the <httpCompression> element at the applicationHost.config level.

So there are two possible solutions. First, you could change your WCF response to use a MIME type that is compressible in the default configuration. text/json will work so adding this to your service method(s) will give you dynamic compression: WebOperationContext.Current.OutgoingResponse.ContentType = "text/json";

Alternatively, you could change the applicationHost.config file using appcmd and a startup task. This is discussed (among other things) on this thread. Note that if you add that startup task and run it in the dev fabric, it will work once. The second time it will fail because you already added the configuration element. I ended up creating a second cloud project with a separate csdef file, so that my devfabric would not run that startup script. There are probably other solutions though.

Update

My suggestion for separate projects in the previous paragraph is not really a good idea. Non-idempotent startup tasks are a very bad idea, because some day the Azure fabric will decide to restart your roles for you, the startup task will fail, and it'll go into a recycle loop. Most likely in the middle of the night. Instead, make your startup tasks idempotent as discussed on this SO thread.

To deal with local development fabric having issues after first deploy, I added the appropriate commands to the CMD file to reset config. In addition, I'm setting compression level here specifically, since it appears to default to zero in some (all?) cases.

REM Remove old settings - keeps local deploys working (since you get errors otherwise)%windir%\system32\inetsrv\appcmd reset config -section:urlCompression%windir%\system32\inetsrv\appcmd reset config -section:system.webServer/httpCompression REM urlCompression - is this needed?%windir%\system32\inetsrv\appcmd set config -section:urlCompression /doDynamicCompression:True /commit:apphostREM Enable json mime type%windir%\system32\inetsrv\appcmd set config -section:system.webServer/httpCompression /+"dynamicTypes.[mimeType='application/json; charset=utf-8',enabled='True']" /commit:apphostREM IIS Defaults%windir%\system32\inetsrv\appcmd set config -section:system.webServer/httpCompression /+"dynamicTypes.[mimeType='text/*',enabled='True']" /commit:apphost%windir%\system32\inetsrv\appcmd set config -section:system.webServer/httpCompression /+"dynamicTypes.[mimeType='message/*',enabled='True']" /commit:apphost%windir%\system32\inetsrv\appcmd set config -section:system.webServer/httpCompression /+"dynamicTypes.[mimeType='application/x-javascript',enabled='True']" /commit:apphost%windir%\system32\inetsrv\appcmd set config -section:system.webServer/httpCompression /+"dynamicTypes.[mimeType='*/*',enabled='False']" /commit:apphost%windir%\system32\inetsrv\appcmd set config -section:system.webServer/httpCompression /+"staticTypes.[mimeType='text/*',enabled='True']" /commit:apphost%windir%\system32\inetsrv\appcmd set config -section:system.webServer/httpCompression /+"staticTypes.[mimeType='message/*',enabled='True']" /commit:apphost%windir%\system32\inetsrv\appcmd set config -section:system.webServer/httpCompression /+"staticTypes.[mimeType='application/javascript',enabled='True']" /commit:apphost%windir%\system32\inetsrv\appcmd set config -section:system.webServer/httpCompression /+"staticTypes.[mimeType='*/*',enabled='False']" /commit:apphostREM Set dynamic compression level to appropriate level.  Note gzip will already be present because of reset above, but compression level will be zero after reset.%windir%\system32\inetsrv\appcmd.exe set config -section:system.webServer/httpCompression /+"[name='deflate',doStaticCompression='True',doDynamicCompression='True',dynamicCompressionLevel='7',dll='%%Windir%%\system32\inetsrv\gzip.dll']" /commit:apphost%windir%\system32\inetsrv\appcmd.exe set config -section:system.webServer/httpCompression -[name='gzip'].dynamicCompressionLevel:7 /commit:apphost