Show production readiness: "I layer Express middleware for auth, validation, and rate limiting. Services are stateless so I scale horizontally behind a load balancer. Redis handles sessions and caching."
Structure: separate routes, controllers, services, and data access layers. Authentication: JWT or session-based depending on client type, middleware-based auth checks. Scaling: cluster mode or PM2 for multi-core, stateless design for horizontal scaling, Redis for session storage, connection pooling for databases. Strong candidates discuss: middleware patterns (Express/Fastify), input validation (Zod/Joi), rate limiting, graceful shutdown, health checks, and structured logging.
Senior Node.js question. Candidates who put everything in route handlers will create unmaintainable code. Those who discuss layered architecture, stateless design, and operational concerns (logging, health checks, graceful shutdown) are production-ready.