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Hi Rene,

To enable gzip compression, you only need to make a few changes to web.config (assuming that the site is hosted on IIS 7).

Static content (js, css, ...)

Add the following under system.webServer section in web.config

<httpCompression minFileSizeForComp="1024">
      <scheme name="gzip" dll="%Windir%\system32\inetsrv\gzip.dll" />
      <staticTypes>
        <add mimeType="text/*" enabled="true" />
        <add mimeType="message/*" enabled="true" />
        <add mimeType="application/javascript" enabled="true" />
        <add mimeType="application/x-javascript" enabled="true" />
        <add mimeType="application/json" enabled="true" />
        <add mimeType="*/*" enabled="false" />
      </staticTypes>
    </httpCompression>
<urlCompression doStaticCompression="true" />

Dynamic content

For dynamic compression, I will recommend that you use the HttpCompression module that is enabled in Dynamicwebs default web.config, because IIS compression can cause problems in the administration (maybe not anymore?).

Another option is to use IIS compression for the front end, but not the administration. You can do that by adding a different web.config to the admin folder.

The HttpCompression module (not IIS compression) is set up to use deflate compression by default. To make it use gzip compression, you change the HttpCompressionPreferredAlgorithm setting under appSettings in web.config:

<add key="HttpCompressionPreferredAlgorithm" value="gzip" />

I have attached the modified web.config (DW 8 + IIS7).

For details about the IIS compression settings, have a look here: http://www.iis.net/configreference/system.webserver/httpcompression

/Morten

My 2 cents...

I think the best way to accomplish this is to have appropriate default settings in applicationHost.config (app host level) and allow overrides in web.config (application level) - at least on dedicated servers.

I've had some issues with this on HN servers, because by default most overrides are denied in web.config (settings are ignored), so I had to modify applicationHost.config in order to get gzip compression on all static files and various other stuff.

As an example, the correct MIME type for .svg files is image/svg+xml, which is not gzip compressed when using the default settings in IIS. Usually, you can't change this behaviour by simply modifying web.config, because overrides are denied :/

What I usually do (on dedicated servers) is...

1) Allow overrides in applicationHost.config

BEFORE: 

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

AFTER:

<section name="httpCompression" allowDefinition="MachineToApplication" overrideModeDefault="Allow" />

2) Modify web.config to include appropriate default settings, more or less the ones used in H5BP web.config. Those default settings could be added to applicationHost.config instead.

3) Add a few lines in web.config, in order to avoid a broken DW administration (reverting any setting that causes problems)...

<configuration>
    ...
    <location path="Admin">
        <system.webServer>
            ... revert settings ...
        </system.webServer>
    </location>
    <location path="CustomModules">
        <system.webServer>
            ... revert settings ...
        </system.webServer>
    </location>
</configuration>

BR, Morten