Design a Distributed Job Scheduler
Last Updated: December 30, 2025
What is a Job Scheduler?
A Job Scheduler is a system that manages the execution of tasks at specified times or intervals. Unlike a task queue where jobs are executed immediately upon submission, a job scheduler allows you to define when a job should run, whether that's a one-time execution in the future or a recurring pattern like "every day at midnight."
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The core idea is to decouple the job definition from its execution. Users define what should run and when, and the scheduler ensures it happens reliably, even across distributed systems where multiple servers need to coordinate to prevent duplicate executions.
Popular Examples: Linux Cron, Kubernetes CronJobs, Apache Airflow, AWS EventBridge Scheduler, Quartz Scheduler
What makes this interesting from a system design perspective is the distributed coordination challenge. When you have multiple scheduler instances running for high availability (and you should), how do you ensure each job executes exactly once? If Scheduler A and Scheduler B both detect that a job is due at 9:00 AM, you need to prevent them from both executing it.
This coordination problem, combined with the complexities of time zones, daylight saving, and failure recovery, makes job schedulers a rich topic for system design discussions.
In this article, we will explore the high-level design of a distributed job scheduler.
Let's start by clarifying the requirements.