iis - Azure Website slow to serve static JS/CSS but not binary

Question

I have an Azure Website/Web App that is incredibly slow to serve static JS and CSS files but seems perfectly fine serving binary.

To test the problem I uploaded two 30MB files, one big.js and the other big.rar. The JS file downloads at around 100KB/s if I'm lucky. The RAR file downloads at around 4,000KB/s. The results are extremely consistent.

I've checked in Fiddler and gzip compression is occurring in both cases. As expected, the JS file is being sent with the MIME type application/x-javascript whereas the RAR file is being served as application/octet-stream.

I am struggling to understand this - why would IIS serve one type of static content so much slower than another?

Answer 1

We had this issue, and was able to resolve this with the help of Azure Support Team. The issue was that the slow files would use TransferEncoding: Chuncked. They suggested that we force static compression to get around this issue.

We had to add the following to <system.webServer>:

<serverRuntime enabled="true"  frequentHitThreshold="1"  frequentHitTimePeriod="00:00:20" />