Certificate expiry at scale
At 00:00 UTC on the 1st of the month, every call from your services to one internal downstream API starts failing simultaneously and completely — 100% error rate, instant, across all regions at once. The errors are TLS handshake failures: `certificate has expired`. No deploy went out; nothing changed in your code; it broke at a clean clock boundary. The downstream team is paged too. Triage, mitigate, and describe the prevention angle.
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.
0:00 of about 30 min
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.