Monitoring, metrics, tracing (OpenTelemetry etc)?

Short answer: Monitor app health, request metrics, errors. Use OpenTelemetry for distributed tracing. Integrate with Application Insights, Prometheus, Grafana.

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.