A recent post by Scott had me look into how our IIS 7 servers were configured. Turns out we were not using dynamic compression (Ok, I already knew that as I’m the one who set them up), so I decided to go about installing the dynamic compression module (you can always un-enable it).

If you already have IIS 7 installed, you can go into the Role Manager and add a role service. The dynamic compression is under the performance section. Once installed, you will need to enable it via the IIS 7 management tool, or use the following command line option:

appcmd set config -section:urlCompression /doDynamicCompression:true 

The appcmd command line tool lives in C:\windows\system32\inetsrv, which is not included in PATH. You will want to review the httpCompression section in C:\Windows\System32\Inetsrv\Config\applicationHost.config to view what Mime types are compressed. By default, when you install dynamic compression, you get the following settings:

<dynamicTypes>
     <add mimeType="text/*" enabled="true" />
     <add mimeType="message/*" enabled="true" />
     <add mimeType="application/x-javascript" enabled="true" />
     <add mimeType="*/*" enabled="false" />
</dynamicTypes>

I couldn’t find a page that specifically listed mimeTypes in the context of IIS 7, but here is the full list of MimeTypes itself which should give you an idea of how you can configure compression.

As Scott points out in his article, you should make an attempt to justify your change, which I did by performing a simple test using a large web page (1.3 MB) we serve up, and noting the response size and time using Fiddler.

The 1.3 MB web page originally took 30 seconds to receive (I know, there is something funny going on with the network connection somewhere, but it does easily illustrate the savings compression gives). Enabling compression shrunk the response to 130KB, taking only 6 seconds.

For some additional information on compression in IIS 7 check out this blog entry by Kanwalijeet Singla.