redirecting users if server is overcrowded or busy using php?

Question

is it possible to use php to redirect users to page i.e. busy.php when the server is busy or overcrowded, or something similiar? thanks :))

Answer 1

I second using a dedicated load balancer instead of doing this with PHP. But if this is not an option for some reason, you can try with sys_getloadavg:

Returns three samples representing the average system load (the number of processes in the system run queue) over the last 1, 5 and 15 minutes, respectively.

Example from Manual:

<?php
$load = sys_getloadavg();
if ($load[0] > 80) {
    header('HTTP/1.1 503 Too busy, try again later');
    die('Server too busy. Please try again later.');
}
?>

The implementation in php-src uses getloadavg under the hood. So the values returned are the same you'd get from running cat /proc/loadavg or uptime.

A simple explanation of Linux load averages can be found at http://blog.scoutapp.com/articles/2009/07/31/understanding-load-averages:

On multi-processor system, the load is relative to the number of processor cores available. The "100% utilization" mark is 1.00 on a single-core system, 2.00, on a dual-core, 4.00 on a quad-core, etc.

Also see https://superuser.com/questions/23498/what-does-load-average-mean-on-unix-linux