loadcheck.php

/*
This script uses the sys_getloadavg() function 
to lock out some visitors in cases of extreme load.

$threads defines the maximum avaialable count of php threads 
to aproximate a representation of the stresslevel.
A good value is the number of cpu threads available to php.

by malte buttjer
buttjer.net
*/

<?

class Loadcheck {

  static private $threads;

  static public function start( $threads = 12 ) {
    self::$threads = $threads;

    if( self::test() ) return;
    http_response_code( 503 );
    die();
  }

  static private function test() {
    if ( self::isVIRoute() ) return TRUE;
    if ( self::isDenied() ) return FALSE;
    if ( self::isStressed() ) return FALSE;
    return TRUE;
  }

  static private function isDenied() {
    return isset( $_COOKIE['denied'] );
  }

  static private function isVIRoute() {
    $routes = ['cart/placeorder']; //Very important payment routes
    return in_array( $_SERVER['REQUEST_URI'], $routes );
  }

  static private function isStressed() {
    $stressLevel = self::getStressLevel( self::$threads );
    
    // $_COOKIE['cartSessionCookie'] is the session cookie of the cart. 
    // Customers with an active cart arent locked out in the first place
    
    if ( $stressLevel === 1 && !isset( $_COOKIE['cartSessionCookie'] ) ) {
      setcookie('denied', 'denied', time()+3*60); //lock for 3min
      return TRUE;
    }
    if ( $stressLevel === 2 && !isset( $_COOKIE['cartSessionCookie'] ) ) {
      setcookie('denied', 'denied', time()+5*60); //lock for 5min
      return TRUE;
    }
    if ( $stressLevel === 2 ) {
      setcookie('denied', 'denied', time()+60); //lock for 1min
      return TRUE;
    }

    return FALSE;
  }

  static private function getStressLevel( $threads ) {
    $load = sys_getloadavg();
    if ( $load[0] > $threads * 0.95 ) return 2; //EXTREME
    if ( $load[0] > $threads * 0.8 ) return 1; //VERY
    return 0; //CHILLED
  }
}