The cluster module enables creating child processes that share server ports, allowing Node.js applications to utilize multiple CPU cores.
Basic Setup#
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Worker Management#
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Auto-Restart Workers#
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Graceful Shutdown#
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Inter-Process Communication#
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Load Balancing#
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Zero-Downtime Restart#
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Shared State with External Store#
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Worker Health Checks#
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Best Practices#
Setup:
✓ Fork based on CPU count
✓ Implement auto-restart
✓ Handle graceful shutdown
✓ Use external state storage
Communication:
✓ Keep messages small
✓ Use structured message types
✓ Handle message errors
✓ Implement timeouts
Reliability:
✓ Health checks
✓ Zero-downtime restarts
✓ Crash recovery
✓ Resource limits
Avoid:
✗ Sharing memory between workers
✗ Too many workers
✗ Ignoring worker crashes
✗ Long-running synchronous code
Conclusion#
The cluster module enables horizontal scaling by utilizing multiple CPU cores. The primary process manages worker processes that share server ports. Implement auto-restart for crashed workers, graceful shutdown for deployments, and health checks for reliability. Use external stores like Redis for shared state since workers have separate memory spaces. For production, consider process managers like PM2 that handle clustering automatically.