IIS Compression in IIS6.0

You can save a lot of bandwidth (though not on latency) by compressing the responses from IIS 

First, before anything else, backup the metabase. This is done by right-clicking on the server in the IIS snap-in and selecting All Tasks -> Backup/Restore Configuration. The rest is straight forward.

IIS changes

1. Right-click the server node and choose Properties
2. Tick the "Enable Direct Metabase Edit"

Create Compression Folder (optional)

Create a folder where the static file compression will be cached, you can call it anything you want or leave the default of “\IIS Temporary Compressed Files” if that works for you. The IUSR_{machinename} will need write permission to the folder. If you use custom anonymous users, make sure to assign the proper user. IIS will still work even if the permissions are wrong but the compression won't work properly. Once running, it's worth double checking Event Viewer to see if any errors are occurring that keep IIS Compression from working.

Enable Compression in IIS

From the IIS snap-in, right-click on the Web Sites node and click on Properties
Select the Service tab:

• Enable Compress application files
• Enable Compress static files
• Change Temporary Directory to the folder that you created above, or leave it at it's default
• Set the max size of the temp folder to something that the hard drive can handle. i.e. 1000.

Save and close the Web Site Properties dialog
Note - The temporary compress directory is only used for static pages. Dynamic pages aren't saved to disk and are recreated every time so there is some CPU overhead used on every page request for dynamic content.

Create a Web Service Extension (WSE)

IIS6.0 is much more proactive than IIS5 in regards to security and introduces a new feature called Web Service Extensions. This is great but means an extra step.

In the IIS snap-in select Web Service Extensions
Create a new web service extension
Call it HTTP Compression
Point it to c:\windows\system32\inetsrv\gzip.dll
Check the Set status checkbox so that it is enabled (Allowed)
Enable Direct Metabase Edit

Download IIS 6.0 Resource Kit from Microsoft it can help you administer, secure, and manage IIS. It also lets you edit and save changes to the Metabase.xml file:

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Settings for LM\w3svc\Filters\Compression\deflate

Make sure the values here are correct. HcDynamicCompressionLevel has a default value of 0. Basically this means at if you did everything else right, the compression for dynamic contact is at the lowest level. The valid range for this is from 0 to 10. I had the opportunity of receiving an internal testing summary from Chris Adams from Microsoft regarding the compression level vs- CPU usage which showed that the CPU needed for levels 0 9 is fairly low but for level 10 it hits the roof. Yet the compression for level 9 is nearly as good as level 10. I write all this to say that I recommend level 9 so make sure to change HcDynamicCompressionLevel to 9. Do this for both deflate and gzip.

HcFileExtensions Properties

1. htm
2. html
3. aspx
4. asmx
5. js
6. css
7. ashx
8. axd
9. txt

HcScriptFileExtensions Properties

1. asp
2. dll
3. aspx
4. asmx
5. js
6. css
7. ashx
8. axd
9. exe

Settings for LM\w3svc\Filters\Compression\gzip

Use the same settings for File Extensions as in the previous section (deflate)

Make sure the values here are correct. HcDynamicCompressionLevel has a default value of 0. Basically this means at if you did everything else right, the compression for dynamic contact is at the lowest level. The valid range for this is from 0 to 10. I had the opportunity of receiving an internal testing summary from Chris Adams from Microsoft regarding the compression level vs- CPU usage which showed that the CPU needed for levels 0 9 is fairly low but for level 10 it hits the roof. Yet the compression for level 9 is nearly as good as level 10. I write all this to say that I recommend level 9 so make sure to change HcDynamicCompressionLevel to 9. Do this for both deflate and gzip.

After these changes have been made, close and restart IIS.

Note - this procedure must be repeated on all web servers in the same cluster.