Why is gzip compression not working on IIS 8.5?

user_653646 0
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I am unable to get gzip compression working on IIS 8.5 on a Server 2012 R2 machine. I have done some research and followed the instructions found in these posts:

  1. How to enable GZIP compression in IIS 7.5
  2. Compression in IIS 8.5 not successful, stating ALREADY_CONTENT_ENCODING
  3. GZip Compression On IIS 7.5 is not working
  4. gzip compression not working with IIS 8.5

Here is the relevant section of my config:

<httpCompression directory="%SystemDrive%\inetpub\temp\IIS Temporary Compressed Files" staticCompressionIgnoreHitFrequency="true">
    <scheme name="gzip" dll="%Windir%\system32\inetsrv\gzip.dll" />
    <!-- I have read that dynamic compression increases server CPU load.
    <dynamicTypes>
        <add mimeType="text/*" enabled="true"/>
        <add mimeType="message/*" enabled="true"/>
        <add mimeType="application/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>
<urlCompression doStaticCompression="true" doDynamicCompression="true" />

Also, in IIS, I set compression to apply to anything larger than 256 bytes. And I have performed iisreset.

Nonetheless, I don't see the compression mentioned in my dev console in Chrome or IE and PageSpeed still tells me to compress stuff. What simple step have I missed?

iis-8.5 http-compression gzip iis asp.net
3 Answers

As mentioned in answers to one of the questions the OP links to, be sure to check for any anti-virus software running on the server. In my case it was ESET. None of the IIS compression settings had an effect until the relevant ESET settings were disabled.

I'm leaving out details of the settings- I did what seemed like a pretty blanket disable and left it to IT to figure out which exact setting was most appropriate for compression to still work while retaining security.

user_80104480

I had a similar issue and was caused by ESET with some strange behavior. It worked on some machines but not on the one with eset, it took me some time to realize.

What happened is that ESET caused chrome to downgrade http2 requests to http 1.1 and not compress them. It can be seen if you open network and enable 'protocol' column. After removing eset it worked even if I forced chrome to use http1.1 with '--disable-http2' flag

Anyway if it still not working I would try to (in addition to the other answers):

  • check if different clients behave the same (in my case only dev machine had the issue)
  • deploy a simple static site (event default one) and test
  • reinstall iis
  • check settings on iss server manager, configuration editor / system.webServer/httpCompression collection, change compression level
user_16121330
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