Load Balanced Cron Task

Introduction

This is a lightweight package for load balancing your cron tasks. It is used to distribute tasks across a network of identical servers to make sure they are run only once and not multiple times.

It is important that your application network uses only one single central mysql database. A table is created in the database in which current tasks are inserted. A primary key ensures that the task only runs once (a kind of locking process).

the unique_hash is a md5 hash of the task name, the schedule and the current timestamp without seconds. With this, the nodes can run asynchronously but the task runs only once at a time.

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Scheme of operation

Requirements

• MySQL Database
• PHP PDO Extension (ext-pdo, ext-pdo_mysql)

1. Installation

1.1 Composer

Install Load Balanced Cron Task using Composer.

$ composer require incapption/load-balanced-cron-task

1.2 Create MySQL Table

This package needs a small table in your database. It's used for locking running tasks, to make sure that only on app instance could run it.

CREATE TABLE IF NOT EXISTS `lbct_tasks` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`unique_hash` varchar(32) NOT NULL,
`task` varchar(256) NOT NULL,
`schedule` varchar(256) NOT NULL,
`date_created` datetime NOT NULL,
`worker` varchar(256),
PRIMARY KEY (`unique_hash`),
KEY `id` (`id`)
);

1.3 Install Crontab

The idea is that you have only one single cron task running every minute. This cron task contains all other tasks wrapped by LoadBalancedCronTask

Open your crontab console (e.g. linux: crontab -e)

* * * * /usr/bin/php /your/local/path/cron.php

1.4 Create your cron file

Maybe you want to integrate into your application, or you create a new plain file.

<?php

use Incapption\LoadBalancedCronTask\Abstracts\CronTaskAbstract;
use Incapption\LoadBalancedCronTask\LoadBalancedCronTask;
use Incapption\LoadBalancedCronTask\Exceptions\LoadBalancedCronTaskException;

require_once('./vendor/autoload.php');

class TestCronTask extends CronTaskAbstract
{
    public function __construct()
    {
        $this->name = 'TestCronTask';
    }

    public function task(): bool
    {
        // do your cron task
        return file_put_contents('test.html', 'awesome! it works! '.date('Y-m-d H:i:s', time()));
    }
}

try {
    $response = (new LoadBalancedCronTask())
        ->mysql($_ENV['MYSQL_HOST'], $_ENV['MYSQL_USER'], $_ENV['MYSQL_PASSWORD'], $_ENV['MYSQL_DATABASE'])
        ->setWorkerName('Node 1')
        ->task((new TestCronTask()))
        ->loadBalanced()
        ->everyMinute()
        ->run();
} catch (LoadBalancedCronTaskException $e) {
    exit($e->getMessage());
}

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2. How to use it

As shown in the example above you need to create classes for your cron tasks that extends CronTaskAbstract. Define the behavior in the task() method.

Second create the load balanced cron task.

# Example for a distributed load balanced cron task
 
$response = (new LoadBalancedCronTask())
    ->mysql($_ENV['MYSQL_HOST'], $_ENV['MYSQL_USER'], $_ENV['MYSQL_PASSWORD'], $_ENV['MYSQL_DATABASE'])
    ->setWorkerName('Node 1')
    ->task((new TestCronTask()))
    ->loadBalanced()
    ->everyMinute()
    ->run();

# Example for a local cron task
 
$response = (new LoadBalancedCronTask())
    ->task((new TestCronTask()))
    ->local()
    ->everyMinute()
    ->run();

2.1 Chainable methods

General:

Method	Description
->mysql(string $host, string $user, string $password, string $database)	Sets the mysql credentials for the underlying pdo instance
->setWorkerName(string $name)	Sets the name of the current worker. Perhaps you will use a environment variable
->task(CronTaskAbstract $task)	Awaits an instance of CronTaskAbstract
->local()	Sets the cron task to local. No distributing and load balancing is taking place. Useful for node specific tasks such as cleaning local tmp folder etc.
->loadBalanced()	Sets the cron task to load balanced. The task is distributed around the network. Only one worker runs the task at a time.

Scheduling methods:

Method	Description
->everyMinute()	Run the task every minute
->everyTwoMinutes()	Run the task every two minutes
->everyThreeMinutes()	Run the task every three minutes
->everyTenMinutes()	Run the task every five minutes
->everyFifteenMinutes()	Run the task every fifteen minutes
->everyThirtyMinutes()	Run the task every thirty minutes
->hourly()	Run the task every hour
->hourlyAt(17)	Run the task every hour at 17 minutes past the hour
->daily()	Run the task every day at 00:00
->dailyAt('17:13')	Run the task every day at 17:13 o'clock
->monthly()	Run the task on the first day of every month at 00:00
->monthlyOn(4, '15:00')	Run the task every month on the 4th at 15:00
->lastDayOfMonth('15:00')	Run the task on the last day of the month at 15:00
->lastDayOfMonthOffset(2, '15:00')	Run the task on the last day of the month at 15:00 with an offset of 2 days. As an example: lastDayOfMonthOffset(2, '15:00') in january, which has 31 days, runs on the 29th at 15 o'clock

Be careful with the days 29th, 30th, 31st if you use monthlyOn(). Maybe use lastDayOfMonth() or lastDayOfMonthOffset() instead.

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3. Exceptions

An instance of LoadBalancedCronTask() throws a LoadBalancedCronTaskException when there is something wrong inside the logic for everything else you can use the default PHP Exceptions.