GZip Compression On IIS 7.5 is not working

Question

I am trying to support GZip compression for my static files under IIS (which should be enabled by default but not) but not working so far. Here is the the section under <system.webServer> node inside the web.config file of the web app;

<httpCompression directory="%SystemDrive%\inetpub\temp\IIS Temporary Compressed Files">
  <scheme name="gzip" dll="%Windir%\system32\inetsrv\gzip.dll" staticCompressionLevel="9" />
  <dynamicTypes>
    <add mimeType="text/*" enabled="true" />
    <add mimeType="message/*" enabled="true" />
    <add mimeType="application/x-javascript" enabled="true" />
    <add mimeType="application/json" enabled="true" />
    <add mimeType="*/*" enabled="false" />
  </dynamicTypes>
  <staticTypes>
    <add mimeType="text/*" enabled="true" />
    <add mimeType="message/*" enabled="true" />
    <add mimeType="application/x-javascript" enabled="true" />
    <add mimeType="application/atom+xml" enabled="true" />
    <add mimeType="application/xaml+xml" enabled="true" />
    <add mimeType="*/*" enabled="false" />
  </staticTypes>
</httpCompression>

<urlCompression doStaticCompression="true" />

I tried it with Google Chrome. Here are the Request Headers;

Accept:text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8

Accept-Charset:ISO-8859-1,utf-8;q=0.7,*;q=0.3

Accept-Encoding:gzip,deflate,sdch

Accept-Language:en-US,en;q=0.8

Cache-Control:no-cache

Connection:keep-alive

Host:my-website-url

Pragma:no-cache

User-Agent:Mozilla/5.0 (Windows NT 6.0) AppleWebKit/534.30 (KHTML, like Gecko) Chrome/12.0.742.122 Safari/534.30

These are the Response Headers;

Accept-Ranges:bytes

Content-Length:232651

Content-Type:application/x-javascript

Date:Thu, 04 Aug 2011 08:58:19 GMT

ETag:"a69135734a50cc1:0"

Last-Modified:Mon, 01 Aug 2011 12:56:37 GMT

Server:Microsoft-IIS/7.5

X-Powered-By:ASP.NET

I check the applicationHost.config file and found some nodes like below;

----

<section name="httpCompression" allowDefinition="AppHostOnly" overrideModeDefault="Deny" />

----

<section name="urlCompression" overrideModeDefault="Allow" />

----

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

----

<urlCompression />

What am I missing here?

I'm having the saame problem. No matter what I do, it will not compress anything, according to Wireshark. — Brain2000

Brain2000 Brain2000 · Accepted Answer · 2013-03-25T23:53:55

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.

GZip Compression On IIS 7.5 is not working

6 Answers