I made some changes to the
web.config of a server running IIS 7.5 improve the performance (mostly front-end).
A 3rd party testing tool says the site is running "PHP/5.3.10, ASP.NET" and if memory serves, it is ASP.NET 4.5
I think it's due to the odd mix of technologies (e.g. running PHP on IIS) but touching anything makes me nervous.
I added (only) the directives for expires headers and gzip from the H5BP IIS server config
I think I added those directives on the afternoon of Jan. 15th 2013. The test history of the site from the Pingdom performance testing tool is available here.
You can see where the transfer size sharply drops off (click on the history tab).
Since then it seems like every time I test it, different files (generally assets like CSS & JS) are or aren't served with gzip with no rhyme or reason. Sometimes everything seems to be served with gzip, sometimes almost nothing seems to be served compressed but it's usually somewhere in the middle (as you can see in the history).
What is going on?
How can I fix it?
This site is not under active development, while some extra data has been added to the page (Google Analytics plugin scripts I added to improve tracking) after the 15th, there is nothing that should explain such large variations and inconsistencies.
My best guess is that it is related to CPU resources for compression, and this question seems close: Why is gzip compression varying in efficiency in IIS?