During a meeting at work today, we looked at my web site (as an example) to see if there are ways the performance could be improved. I was surprised to see how many things could be done to make it a big faster.
One of the most trivial changes involved adding an Expires: header which specifies a time far enough in the future so that clients (browsers) won’t try to re-fetch images that haven’t changed.
Since I’m running Apache 1.3, I dug up the old documentation on mod_expires and made a few simple additions to httpd.conf:
ExpiresActive On ExpiresByType image/gif A2592000 ExpiresByType image/png A2592000 ExpiresByType image/jpg A2592000 ExpiresByType image/jpeg A2592000
That asks Apache to set an Expires header that’s roughly one month from the moment at which the browser requested the image. Here’s a quick test to show that it worked:
root@litterbox:~/w/i# telnet localhost 80 Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. HEAD /i/mini-softie.jpg HTTP/1.0 Host: hackers.com.pk ... HTTP/1.1 200 OK Date: Mon, 23 Jul 2007 22:03:35 GMT Server: Apache/1.3.34 (Debian) mod_gzip/22.214.171.124a PHP/4.4.4-8 Cache-Control: max-age=2592000 Expires: Wed, 22 Aug 2007 22:03:35 GMT Last-Modified: Tue, 29 May 2007 15:51:04 GMT ETag: "95c67-5995-465c4be8" Accept-Ranges: bytes Content-Length: 22933 Connection: close Content-Type: image/jpeg
Excellent. August 22nd is about a month from now.
In theory I could go quite a bit farther into the future since I almost never replace images on my site.