http

A staple of every networking round, and the follow-up is always about TLS termination. Knowing which layer sees what decides most of the answer.

The oldest question in systems interviewing and still the best, because it is unbounded: every layer you can describe is another layer you could debug.

A Service moves connections and an Ingress reads requests. The gap between those two sentences is hostname routing, path routing and TLS, and it is also why an Ingress object alone does nothing.

Status codes describe an HTTP failure category. Locate the component that emitted the response, then use its logs to distinguish connection, capacity and application failures.