Backend fundamentals

Backend fundamentals interviews assess whether you can operate a Node HTTP service as a system: request lifecycle, middleware composition, errors, validation, logging, configuration, environment, and graceful shutdown.

Subtopics: request lifecycle, middleware, error handling, validation, logging, configuration, environment variables, and graceful shutdown.

On interviews: walk a request from socket accept through parsing, auth, validation, handler, response, and cleanup; explain what happens on SIGTERM.

Common pitfalls: fat route handlers, unhandled promise rejections, secrets in logs, missing startup config validation, and hard kills without draining in-flight work.

The trade-off is balancing simplicity, performance, safety, and operability — name which axis you optimized and what cost you accepted.

Checklist:

• Keep cross-cutting concerns in ordered middleware.
• Map operational vs programmer errors to HTTP responses.
• Validate untrusted input at service boundaries.
• Load and validate config once at startup; plan shutdown.