Connection reuse regression
After a routine HTTP-client library upgrade, your service starts seeing a small but steady ~2% rate of connection-reset and 'connection refused' errors to a downstream API, plus a latency bump. The errors climb with traffic. The downstream is healthy and underloaded and reports nothing wrong. CPU/mem are fine. Comparing connection metrics before/after the upgrade, the count of new TCP connections + TLS handshakes per second jumped ~30x, and the average requests-per-connection dropped from ~200 to ~1. There were no other changes. How do you triage and fix?
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 35 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.