Code Room
On-callMedium
Question
Your service connects OUTBOUND to a bank partner's API using a client certificate the partner issued you for mTLS. At 00:00 UTC all calls to the partner start failing with TLS handshake errors; the partner's logs (they shared) say 'client certificate expired.' Your monitoring watches the partner's SERVER cert expiry and the partner's endpoint is healthy and serving. Your own public-facing leaf certs are all fine and freshly renewed. The partner integration has worked untouched for a year. How do you triage and mitigate?
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.
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