Code Room
On-callHardoc-g459
Subject Error rate spikesLevel Senior–Staff~40 minCommon in Reliability & on-call interviewsIndustries Technology, Software development

Question

After a coordinated full restart of your TLS-terminating edge fleet (a fast rolling restart that cycled almost all nodes within a couple minutes), you see a few minutes of elevated p99, raised CPU on the edge nodes, and a spike of client handshake errors/timeouts — even though traffic volume is unchanged. Metrics show TLS session-resumption RATE collapsed to near zero right after the restart and then climbed back over ~5 minutes, exactly tracking the error/CPU spike as it subsided. New full handshakes per second jumped enormously during the window. 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.

Diagram & narrate the incident
Loading whiteboard…
Run or narrate your approach, then ask the coach.