We have much the same setup (nginx -> IIS6) and compression works
fine. However, you have quite a few items in your gzip config that are
probably unnecessary, and might be causing issues.
I would first use a tool like Fiddler (www.fiddler2.com) rather than a
3rd party site for testing. You can see if a response is compressed
using the inspector section on the right side of the fidder window.
Secondly, try commenting out all your gzip-related settings except
"gzip on" and make sure it works with that.
Third, you likely don't want "gzip_comp_level 8", as it burns a lot of
CPU for saving maybe 5-10% size over the default setting (which is
Finally, add back your additional gzip-related settings until you
start to see uncompressed responses.