Enable Browser Caching For Static Resources

To improve the site performance, I'm adding following http headers in IIS 7.5. Expires: Sun, 29 Mar 2020 00:00:00 GMT and Cache-Control: Public I'm adding these headers for image

Solution 1:

Your header shows that you add a new value but you need to replace the existing one

Cache-Control:no-cache, no-store,Public
Expires:-1,Sun, 29 Mar 2020 00:00:00 GMT

no-cache, no-store stands for no cache and -1 says that the content is already expired.

Instead of doing it from the code you can easily set it in the root web.config file as

  <location path="images">
    <system.webServer>
      <staticContent>
        <clientCache cacheControlMode="UseExpires" 
                     httpExpires="Sun, 29 Mar 2020 00:00:00 GMT" /> 
      </staticContent>
    </system.webServer>
  </location>
</configuration>

where images is a name of your directory

or add dedicated web.config file directly in the target directory

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <system.webServer>
    <staticContent>
      <clientCache cacheControlMode="UseExpires" 
                   httpExpires="Sun, 29 Mar 2020 00:00:00 GMT" /> 
    </staticContent>
  </system.webServer>
</configuration>

You can also use cacheControlMode="UseMaxAge" and set specific time of expiration

Example to set expiration in 7 days

<clientCache cacheControlMode="UseMaxAge" 
             cacheControlMaxAge="7.00:00:00" /> 

Read more http://msdn.microsoft.com/en-us/library/ms689443.aspx