Agent-Skills.md

Agent Skills: Task Scheduling & Jobs

Implement distributed cron jobs with Redis-based locking and BullMQ offloading in NestJS. Use when adding @Cron scheduled tasks, preventing duplicate runs across pods, or delegating heavy work to queue workers. (triggers: **/*.service.ts, @Cron, CronExpression, ScheduleModule)

UncategorizedID: hoangnguyen0403/agent-skills-standard/nestjs-scheduling

Repository

hoangnguyen0403/agent-skills-standard
HoangNguyen0403License: Apache-2.0
362103

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pnpm dlx add-skill https://github.com/HoangNguyen0403/agent-skills-standard/tree/HEAD/skills/nestjs/nestjs-scheduling

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skills/nestjs/nestjs-scheduling/SKILL.md

Skill Metadata

Name
nestjs-scheduling
Description
"Implement distributed cron jobs with Redis-based locking and BullMQ offloading in NestJS. Use when adding @Cron scheduled tasks, preventing duplicate runs across pods, or delegating heavy work to queue workers. (triggers: **/*.service.ts, @Cron, CronExpression, ScheduleModule)"

Task Scheduling & Jobs

Priority: P1 (OPERATIONAL)

Background job processing and scheduled task patterns.

Workflow: Add a Scheduled Task

  1. Register ScheduleModule — Import ScheduleModule.forRoot() in AppModule.
  2. Create cron handler — Decorate a service method with @Cron(CronExpression.*).
  3. Add distributed lock — Apply a Redis lock decorator to prevent multi-pod duplication.
  4. Offload heavy work — Push job IDs to BullMQ; let workers process them.
  5. Wrap in try/catch — Uncaught exceptions in cron handlers crash the entire Node process.
  6. Verify — Test with 2+ instances to confirm only one acquires the lock.

Problem & Solution

  • 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:

    See implementation examples

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

Cron-to-Queue Offload

See implementation examples

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.

Anti-Patterns

  • No unguarded cron logic: Always wrap in try/catch; uncaught exceptions crash the entire Node process.
  • No direct cron processing: Push to BullMQ queue; workers are scalable, cron handlers are not.
  • No bare @Cron in multi-pod: Use distributed locking (redlock) to prevent duplicate concurrent runs.