GZip Compression On IIS 7.5 is not working

After a lot of searching, I finally found what got compression working on my IIS 7.5.To start with, IIS will not compress a file unless it loaded often enough. That brings up the question "what does IIS consider often enough?" Well, the defaults are 2 times every 10 seconds. Yikes!

This setting can be changed in web.config, but the section needs to be unlocked first in applicationHost.config. Here are the commands:

First unlock the section:

C:\Windows\System32\inetsrv\appcmd.exe unlock config /section:system.webServer/serverRuntime

Unlocked section "system.webServer/serverRuntime" at configuration path "MACHINE/WEBROOT/APPHOST".

Now that is done, edit the web.config file and add the serverRuntime element:

<?xml version="1.0" encoding="UTF-8"?>
  <configuration>
    <system.webServer>
      <serverRuntime frequentHitThreshold="1" frequentHitTimePeriod="10:00:00" />
...

In this case, I set it to hit the file once in a 10 hour period. You can adjust the values as necessary. Here is the document that explains the serverRuntime element:

http://www.iis.net/configreference/system.webserver/serverruntime

I hope this helps get your compression working as well.

Note: you can also set the serverRuntime element up in the applicationHost.config file, but I chose to change it in the web.config because we have a number of servers and farms with various sites, and it is easier for me to control it from this level of granularity.

One thing to keep in mind is that the first hit usually is returned uncompressed immediately, but spins up a thread to compress the file in the background in order to service the response with compression for future requests.

Also, have you tried using a different client (e.g. IE)?

Make sure you install Dynamic Compression on the server. Add/Remove Features under IIS.