loadwatcher.php

<?php

define ("LOAD_AVERAGE_THRESHOLD", 10.0);
define ("APACHE_RESTART_THRESHOLD", 60 * 30);
define ("DEFAULT_LOAD_AVERAGE_PATH", "/proc/loadavg");
define ("APACHE_COMMAND_STOP", '/etc/init.d/apache2 stop');
define ("APACHE_COMMAND_START", '/etc/init.d/apache2 start');
define ("APACHE_COMMAND_RESTART", '/etc/init.d/apache2 restart');
define ("APACHE_COMMAND_STATUS", '/etc/init.d/apache2 status');

function get_current_load_average() {
  $load_average_file_name = DEFAULT_LOAD_AVERAGE_PATH;
  $fp = @fopen($load_average_file_name, 'r');
  if ($fp == null) {
    die("unable to open file at $load_average_file_name\n");
  }
  $load_averages = explode(" ", fread($fp, 4096));
  return floatval($load_averages[0]);
}

function restart_apache_server() {
  // Do some stuff in here!
  printf ("Server might be going through problems...restart the web server now!\n");
  system(APACHE_COMMAND_STOP);
  printf ("Stopped web server");
  sleep(10);
  system(APACHE_COMMAND_START);
  printf ("Started web server");
}

$allowed_restart_time = time();

while (1) {
  $current_load_average = get_current_load_average();
  printf("Current load - %f\n", $current_load_average);
  if ($current_load_average < LOAD_AVERAGE_THRESHOLD) {
    printf ("Server is doing pretty well!\n");
  }
  else if ($current_load_average >= LOAD_AVERAGE_THRESHOLD && time() > $allowed_restart_time) {
    restart_apache_server();
    $allowed_restart_time = time() + APACHE_RESTART_THRESHOLD;
  }
  else {
    printf ("Wait for some time to ensure server is getting back to normal.\n");
  }
  sleep(30);
}