I've set up an Azure CDN using the Standard Akamai tier. My origin is a Web App. I've set up the cache-control header in my web.config as follows:
<clientCache cacheControlMode="UseMaxAge" cacheControlCustom="public" cacheControlMaxAge="30.00:00:00" />
In my markup, I'm hitting my image file with the following code:
<img src="https://xxxx.azureedge.net/Content/Images/Turtle.jpg?v=1.0.0.27987">
When I do so, I get the following response headers:
cache-control:public, max-age=2591903
content-length:2321435
content-type:image/jpeg
date:Mon, 03 Apr 2017 19:34:23 GMT
etag:"2e7a1f1690a9d21:0"
last-modified:Thu, 30 Mar 2017 19:59:05 GMT
pragma:no-cache
server:Microsoft-IIS/8.0 status:200 vary:Accept-Encoding x-powered-by:ASP.NET
Notice the pragma:no-cache. I have NO IDEA where that is coming from. This is definitely NOT in my origin's response to load the cache. If I hit the origin, I see the following headers sent for the same image:
Accept-Ranges:bytes
Cache-Control:public,max-age=2592000
Content-Length:2321435
Content-Type:image/jpeg
Date:Mon, 03 Apr 2017 19:41:50 GMT
ETag:"2e7a1f1690a9d21:0"
Last-Modified:Thu, 30 Mar 2017 19:59:05 GMT
Server:Microsoft-IIS/8.0
X-Powered-By:ASP.NET
This means that when hitting the CDN, instead of serving this image from http cache, it's sending the ETag and I'm wasting a HTTP roundtrip. I'm assuming that the culprit is the pragma:no-cache header that is sent, which is overriding the cache-control header. My questions are:
- Why is the Azure CDN adding this pragma:no-cache header when serving my image?
- Is the pragma:no-cache the reason we're seeing the 304/ETag validation instead of serving from http cache?
Thanks!
Edit: I've also tried removing the tag from the web.config. I'm still seeing an ETag transmitted for the image instead of serving it from the browser http cache.
