[asp.net] IIS7 Cache-Control

I'm trying to do something which I thought would be fairly simple. Get IIS 7 to tell clients they can cache all images on my site for a certain amount of time, let's say 24 hours.

I have tried the step on http://www.galcho.com/Blog/post/2008/02/27/IIS7-How-to-set-cache-control-for-static-content.aspx but to no avail. I still get requests going to the server with 304s being returned.

Does anyone have a way of doing this? I have a graphically intensive site and my users are being hammered (so is my server) every time they request a page. Wierdly the images seem to have "Cache-Control private,max-age=3600" showing up in Firebug but the browser is still requesting them when I press F5.

there is a easy way: 1. using website's web.config 2. in "staticContent" section remove specific fileExtension and add mimeMap 3. add "clientCache"

<configuration>
  <system.webServer>
    <urlCompression doStaticCompression="true" doDynamicCompression="true" />
    <staticContent>
      <remove fileExtension=".ipa" />
      <remove fileExtension=".apk" />
      <mimeMap fileExtension=".ipa" mimeType="application/iphone" />
      <mimeMap fileExtension=".apk" mimeType="application/vnd.android.package-archive" />
      <clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="777.00:00:00" />
    </staticContent>
  </system.webServer>
</configuration>

Complementing Elmer's answer, as my edit was rolled back.

To cache static content for 365 days with public cache-control header, IIS can be configured with the following

<staticContent>
    <clientCache cacheControlCustom="public" cacheControlMode="UseMaxAge" cacheControlMaxAge="365.00:00:00" />
</staticContent>

This will translate into a header like this:

Cache-Control: public,max-age=31536000

Note that max-age is a delta in seconds, being expressed by a positive 32bit integer as stated in RFC 2616 Sections 14.9.3 and 14.9.4. This represents a maximum value of 2^31 or 2,147,483,648 seconds (over 68 years). However, to better ensure compatibility between clients and servers, we adopt a recommended maximum of 365 days (one year).

As mentioned on other answers, you can use these directives also on the web.config of your site for all static content. As an alternative, you can use it only for contents in a specific location too (on the sample, 30 days public cache for contents in "cdn" folder):

<location path="cdn">
   <system.webServer>
        <staticContent>
             <clientCache cacheControlCustom="public" cacheControlMode="UseMaxAge" cacheControlMaxAge="30.00:00:00"/>
        </staticContent>
   </system.webServer>
</location>

I use this

<staticContent>
<clientCache cacheControlCustom="public" cacheControlMode="UseMaxAge" cacheControlMaxAge="500.00:00:00" />
</staticContent>

to cache static content for 500 days with public cache-control header.

That's not true Jeff.

You simply have to select a folder within your IIS 7 Manager UI (e.g. Images or event the Default Web Application folder) and then click on "HTTP Response Headers". Then you have to click on "Set Common Header.." in the right pane and select the "Expire Web content". There you can easily configure a max-age of 24 hours by choosing "After:", entering "24" in the Textbox and choose "Hours" in the combobox.

Your first paragraph regarding the web.config entry is right. I'd add the cacheControlCustom-attribute to set the cache control header to "public" or whatever is needed in that case.

You can, of course, achieve the same by providing web.config entries (or files) as needed.

Edit: removed a confusing sentence :)

The F5 Refresh has the semantic of "please reload the current HTML AND its direct dependancies". Hence you should expect to see any imgs, css and js resource directly referenced by the HTML also being refetched. Of course a 304 is an acceptable response to this but F5 refresh implies that the browser will make the request rather than rely on fresh cache content.

Instead try simply navigating somewhere else and then navigating back.

You can force the refresh, past a 304, by holding ctrl while pressing f5 in most browsers.