Task Scheduling & Jobs

Priority: P1 (OPERATIONAL)

Background job processing and scheduled task patterns.

• •Problem: @Cron() runs on every instance. In K8s with 3 pods, your "Daily Report" runs 3 times.
• •Solution: Distributed Locking using Redis.
  • •Pattern: Using a decorator to wrap the cron method.
  • •Logic: SET resource_name my_random_value NX PX 30000 (Redis Atomic Set).

Cron Decorator Pattern

• •

  Implementation:

  typescript

  @Cron(CronExpression.EVERY_MINUTE)
  @DistributedLock({ key: 'send_emails', ttl: 5000 })
  async handleCron() {
    // Only runs if lock acquired
  }
  

• •

  Tools: Use nestjs-redlock or custom Redis wrapper via redlock library.

Job Robustness

• •Isolation: Never perform heavy processing inside the Cron handler.
  • •Pattern: Cron -> Push Job ID to Queue (BullMQ) -> Worker processes it.
  • •Why: Cron schedulers can get blocked by the Event Loop; Workers are scalable.
• •Error Handling: Wrap ALL cron logic in try/catch. Uncaught exceptions in a Cron job can crash the entire Node process.