How to Turn on IIS7 Compression

One thing you can do to speed up your site is by turning on compression on your web server. This approach is highly recommended by Yahoo in their website performance analysis tool YSLOW as well as Google via PageSpeed.

In essence, compression helps in reducing data payload transmitted between the web server and the client browser. With machines (both the server and client machine) that are relatively powerful nowadays to handle compression easily - this than becomes a very viable and efficient solution to reduce network bottlenecks, thus increasing the perceived response to the browsing experience.

Here is how to do it in IIS7:

1. Open IIS Manager and In "Features" view, double-click Compression. 
2. Choose one or both of the following: 


• Enable dynamic content compression to configure IIS to compress dynamic content. 
• Enable static content compression to configure IIS to compress static content. 


3. Open the configuration file at "C:\Windows\System32\inetsrv\config\applicationhost.config" and make sure your compression settings are correct or if you want to add/remove any compression settings.

Mine looks like this:

 
<httpCompression directory="%SystemDrive%\inetpub\temp\IIS Temporary Compressed Files">
    <scheme name="gzip" dll="%Windir%\system32\inetsrv\gzip.dll" />
    <dynamicTypes>
        <add mimeType="text/*" enabled="true" />
        <add mimeType="message/*" enabled="true" />
        <add mimeType="application/x-javascript" enabled="true" />
        <add mimeType="*/*" enabled="false" />
    </dynamicTypes>
    <staticTypes>
        <add mimeType="text/*" enabled="true" />
        <add mimeType="message/*" enabled="true" />
        <add mimeType="application/javascript" enabled="true" />
        <add mimeType="*/*" enabled="false" />
    </staticTypes>
</httpCompression>

That's it! Easy!

Now one caveat is that it seems that IIS7 does not compress javascript file immediately, so it may need a few hits before you can detect it using fiddler or firebug etc. I waited for about 2-3 days before eventually YSLow and PageSpeed both detect that all my javascript files are compressed.