Job Scheduler

Difficulty: Medium

What It Tests

Distributed cron, fault tolerance, exactly-once execution.

Topics Covered

• Job Scheduling & Background Processing
• Message Queues & Async Processing
• Distributed Locking
• Database Design: SQL vs NoSQL
• Key-Value Stores at Scale (DynamoDB)

Hello Interview Breakdown

Read the full Hello Interview breakdown →

Video Walkthroughs

• Hello Interview: Distributed Job Scheduler →
• Hello Interview: Job Scheduler System Design →

Approach Hints

• Poll a jobs table for due jobs (next_run_at)
• Use a distributed lock to claim a job before execution
• Mark job as running to prevent double-execution
• Exponential backoff for failed jobs; store next_run_at based on cron expression after successful completion