title: Setting the "Expire Web Content" common http response header in IIS
body: <p>We have a fairly high-volume IIS7.0 site (about 1 million requests a day), a lot of which are Images/CSS/JS.</p>
  
  <p>As a quick way to reduce this, I'm considering setting the common http response header to expire web content some fixed date way in the future, and an wondering what possible disadvantages we could get with this.</p>
  
  <p>Looking at the web.config change resulting from setting this, it adds:</p>
  
  <pre><code>&lt;staticContent&gt;
      &lt;clientCache cacheControlMode="UseExpires" cacheControlMaxAge="1.00:00:00" httpExpires="Thu, 01 Oct 2020 00:00:00 GMT" /&gt;
  &lt;/staticContent&gt;
  </code></pre>
  
  <p>My worry is that if we wanted to change one of the CSS/JS/Images after setting this, clients wouldn't pick up the changes and whilst images probably won't change, CSS/JS certainly will. Does that mean we should only set this on for folders containing <em>only</em> images? Or does this mean we need to introduce versioned URLs for our CSS/JS?</p>