Why Switch from Linux Crontab to Workerman Crontab for High‑Availability Scheduling

Job concept

Job represents short‑term tasks; a timed job runs at a predefined time or at a regular interval.

Linux crontab overview

Crontab is a Linux service that creates, edits, and manages scheduled tasks. The crontab command lets a user specify when a command or script should be executed automatically.

Its time expression follows the classic five‑field format (minute, hour, day of month, month, day of week):

# ┌───────────── minute (0‑59)
# │ ┌───────────── hour (0‑23)
# │ │ ┌───────────── day of month (1‑31)
# │ │ │ ┌───────────── month (1‑12)
# │ │ │ │ ┌───────────── day of week (0‑6, Sunday=0, 7 also accepted)
# │ │ │ │ │               or sun,mon,tue,wed,thu,fri,sat
# * * * * *

Typical command examples:

# Daily backup of Nginx logs at 02:00
0 2 * * * /home/tinywan/sh/nginx_log_to_oss.sh 1>> /dev/null 2>&1

# Delete expired download files daily at 23:10
0 23 * * * /usr/local/php-7.4/bin/php think crontab delete-job-file

Crontab operation

The crond daemon loads all scheduled entries from files under /var/spool/cron when it starts. When a task runs, execution logs are written to /var/log/cron.

Crontab limitations

Using crontab has the following pain points:

No high availability: Tasks run only on the machine where the crontab file resides; if that machine fails, the tasks are lost.

No automatic load balancing: Scripts must be manually distributed across servers, increasing operational overhead.

No permission isolation: Developers need direct access to production machines to add or modify jobs, breaking the ops‑dev separation.

Workerman Crontab

Workerman Crontab is a PHP‑based scheduler built on the Workerman event‑driven framework. It supports second‑level granularity, enabling precise timing for tasks that require sub‑minute accuracy.

Time notation (optional seconds field)

0   1   2   3   4   5
|   |   |   |   |   |
|   |   |   |   |   +------ day of week (0‑6, Sunday=0)
|   |   |   |   +------ month (1‑12)
|   |   |   +-------- day of month (1‑31)
|   |   +---------- hour (0‑23)
|   +------------ min (0‑59)
+-------------- sec (0‑59) [optional; if omitted, granularity is minute]

Simple example

<?php
use Workerman\Worker;
require __DIR__ . '/vendor/autoload.php';

use Workerman\Crontab\Crontab;
$worker = new Worker();

// Set timezone to avoid unexpected results
date_default_timezone_set('PRC');

$worker->onWorkerStart = function() {
    // Execute at the 1st second of every minute
    new Crontab('1 * * * * *', function() {
        echo date('Y-m-d H:i:s') . "
";
    });
    // Execute daily at 07:50 (seconds omitted)
    new Crontab('50 7 * * *', function() {
        echo date('Y-m-d H:i:s') . "
";
    });
};

Worker::runAll();

Note: scheduled tasks start counting from the next minute; they do not run immediately upon definition.

Advantages of Workerman Crontab

Second‑level scheduling: Allows tasks to be triggered at specific seconds.

High performance: Event‑driven architecture handles massive concurrent connections and tasks efficiently.

Dynamic management: Tasks can be added, deleted, or modified at runtime without restarting the worker.

Distributed deployment: Jobs can be spread across multiple servers, improving reliability and throughput.

Operational efficiency: Simplifies development, debugging, and monitoring of scheduled jobs within PHP applications.