Node.js powers a large share of modern backend APIs — from startup microservices to large-scale data processing pipelines. Its single-threaded async model is powerful but introduces a category of bugs that do not exist in traditional multi-threaded languages. This guide covers the most common Node.js production issues.
Express issues often involve middleware ordering (error handlers must have four parameters and be registered after routes), async error handling (async route handlers that throw errors not being caught by Express error middleware), and session/cookie configuration in production environments. NestJS issues are often more structural: dependency injection circular dependencies, module resolution failures, and decorator configuration errors.
Node.js async bugs include:
Node.js API performance issues are usually caused by: synchronous operations blocking the event loop (crypto, file system operations in request path), missing database connection pooling (new connection per request), inefficient queries generating too much data, large JSON serialisation overhead, and missing HTTP caching headers.
Node.js memory leaks are common and often subtle. Frequent causes include event listeners that are added but never removed (EventEmitter leak), closures in request handlers that retain large objects longer than needed, global caches with no eviction, and third-party libraries that accumulate state. The --inspect flag and Node.js heap snapshots are the primary diagnostic tools.
Node.js microservices challenges include service-to-service authentication (JWT validation, API key management), inter-service communication timeouts and retry logic, message queue integration (RabbitMQ, Kafka, SQS) with correct ack/nack handling, and distributed tracing setup (OpenTelemetry).
Node.js production deployment issues involve PM2 configuration for multi-core utilisation, graceful shutdown handling (SIGTERM, connection draining), Docker container optimisation (Alpine base images, non-root users), and Kubernetes readiness probes that correctly reflect application health.
Unhandled promise rejections crashing the process, event loop blocking from synchronous operations, memory leaks from event listener accumulation, and connection pool exhaustion from database connection mismanagement.
Use clinic.js flame graphs or the Node.js --prof profiler to identify long-running synchronous operations. Look for large JSON parsing, synchronous file operations, or heavy computation in request handlers that should be offloaded to worker threads.
Event listeners added but never removed, closures retaining large objects, global caches without eviction, and circular references that prevent garbage collection. Use Node.js heap snapshots (via --inspect and Chrome DevTools) to identify growing object types.
Read the circular dependency warning carefully — it names the modules involved. Use forwardRef() to break circular dependencies when they are unavoidable. Verify that all providers are exported from their modules before being imported elsewhere.
Prometheus with prom-client for application metrics, OpenTelemetry for distributed tracing, clinic.js for performance profiling, and PM2 plus for built-in metrics if you use PM2 for process management.
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