I am trying to sort out caching in IIS for my site.

Basically, I want nothing cached, except for .png, .js, and .css files.

At my site level, I opened the HTTP Reponse Headers and used the "Set Common Hedaers..." to set content to expire immediately.

I have no Output Caching profiles set at any level in IIS.

I clear my browser cache then try accessing my site. When my site requests a PNG file, I see responses like:

Accept-Ranges   bytes
Age 0
Connection  Keep-Alive
Content-Type    image/png
Date    Thu, 12 Apr 2012 21:55:15 GMT
Etag    "83b7322de318cd1:0"
Last-Modified   Thu, 12 Apr 2012 19:33:45 GMT
Server  Microsoft-IIS/7.5
X-Powered-By    ASP.NET

For JS and CSS files, I see responses like:

Accept-Ranges   bytes
Cache-Control   no-cache
Connection  Keep-Alive
Content-Encoding    gzip
Content-Length  597
Content-Type    text/css
Date    Thu, 12 Apr 2012 21:55:15 GMT
Etag    "06e45ede15bca1:0"
Last-Modified   Mon, 02 Nov 2009 17:28:44 GMT
Server  Microsoft-IIS/7.5
Vary    Accept-Encoding
X-Powered-By    ASP.NET

Accept-Ranges   bytes
Cache-Control   no-cache
Connection  Keep-Alive
Content-Encoding    gzip
Content-Length  42060
Content-Type    application/x-javascript
Date    Thu, 12 Apr 2012 21:55:14 GMT
Etag    "2356302de318cd1:0"
Last-Modified   Thu, 12 Apr 2012 19:33:45 GMT
Server  Microsoft-IIS/7.5
Vary    Accept-Encoding
X-Powered-By    ASP.NET

So, why are my PNGs able to be cached, but JS and CSS files not?

Then, I go into the Output Caching feature in IIS and set up profiles for .png, .css, and .js files. This updates the web.config file as follows:

<caching>
     <profiles>
           <add extension=".png" policy="CacheUntilChange" kernelCachePolicy="DontCache" />
           <add extension=".css" policy="CacheUntilChange" kernelCachePolicy="DontCache" />
           <add extension=".js" policy="CacheUntilChange" kernelCachePolicy="DontCache" />
     </profiles>
</caching>

I do a "precautionary" IISReset then try accessing my site again.

For PNG files, I see the following response:

Accept-Ranges   bytes
Age 0
Connection  Keep-Alive
Content-Length  3833
Content-Type    image/png
Date    Thu, 12 Apr 2012 22:02:30 GMT
Etag    "0548c9e2c5dc81:0"
Last-Modified   Tue, 22 Jan 2008 19:26:00 GMT
Server  Microsoft-IIS/7.5
X-Powered-By    ASP.NET

For CSS and JS files, I see the following responses:

Accept-Ranges   bytes
Cache-Control   no-cache,no-cache
Connection  Keep-Alive
Content-Encoding    gzip
Content-Length  2680
Content-Type    application/x-javascript
Date    Thu, 12 Apr 2012 22:02:29 GMT
Etag    "0f743af9015c81:0"
Last-Modified   Tue, 23 Oct 2007 16:20:54 GMT
Server  Microsoft-IIS/7.5
Vary    Accept-Encoding
X-Powered-By    ASP.NET



Accept-Ranges   bytes
Cache-Control   no-cache,no-cache
Connection  Keep-Alive
Content-Encoding    gzip
Content-Length  3831
Content-Type    text/css
Date    Thu, 12 Apr 2012 22:02:29 GMT
Etag    "c3f42d2de318cd1:0"
Last-Modified   Thu, 12 Apr 2012 19:33:45 GMT
Server  Microsoft-IIS/7.5
Vary    Accept-Encoding
X-Powered-By    ASP.NET

What am I doing wrong? Have I completely misunderstood the features of IIS, or is there a bug.

Most importantly, how do I achieve what I want - that is get the browser to cache only PNG, JS and CSS files?