If the PHP responses are relatively static, adding a bit of caching in front of it will improve the responsiveness and decrease the load dramatically. Simply adding a 5 minute cache let us scale one PHP application from 100 concurrent to &quot;SSL &amp; gzip require more CPU than PHP&quot;. We figured that was sufficient.<p>More dynamic applications (like a commenting system) might feel better at 10-30 seconds of caching with expiration commands, but it will still help scale up significantly.