On-callEasyoc-g533

Subject Cert expiryLevel Entry–Mid~15 minCommon in Reliability & on-call interviewsIndustries Technology, Software development

Question

An internal API that other teams call started returning connection failures at 2:00am exactly. The callers' logs show TLS handshake errors mentioning an expired certificate, and browsers hitting the endpoint show a 'certificate expired' warning. The service process itself is up and healthy; only the TLS layer is failing. Nothing deployed recently. How do you confirm the cause and restore service?

What a strong answer looks like

Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.

Learn the concepts

Diagram & narrate the incident

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Run or narrate your approach, then ask the coach.