IIS7 Cache-Control

Question

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.

Answer 1

If you want to set the Cache-Control header, there's nothing in the IIS7 UI to do this, sadly.

You can however drop this web.config in the root of the folder or site where you want to set it:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <system.webServer>
    <staticContent>
      <clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="7.00:00:00" />
    </staticContent>
  </system.webServer>
</configuration>

That will inform the client to cache content for 7 days in that folder and all subfolders.

You can also do this by editing the IIS7 metabase via appcmd.exe, like so:

\Windows\system32\inetsrv\appcmd.exe 
  set config "Default Web Site/folder" 
  -section:system.webServer/staticContent 
  -clientCache.cacheControlMode:UseMaxAge

\Windows\system32\inetsrv\appcmd.exe 
  set config "Default Web Site/folder" 
  -section:system.webServer/staticContent 
  -clientCache.cacheControlMaxAge:"7.00:00:00"

Answer 2

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 :)

Answer 3

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.

Answer 4

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>