GZip Compression On IIS 7.5 is not working
Solution 1:
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.
Solution 2:
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)?
Solution 3:
Make sure you install Dynamic Compression on the server. Add/Remove Features under IIS.
Solution 4:
Took me a while to figure this out too. Setting the frequentHitThreshold attribute to 1 on the system.webServer/serverRuntime node in the applicationHost.config file should do the trick, as documented at http://www.iis.net/ConfigReference/system.webServer/serverRuntime.
You can do this by executing the following command as an administrator:
%windir%\system32\inetsrv\appcmd set config /section:serverRuntime /frequentHitThreshold:1 /commit:apphost
A word of warning - the "frequent hit" concept does not seem specific to compression. I have no idea whether there are other consequences as a result of setting this!