Code RoomPredictable traffic spike causes 503s
MediumPrep Room Coding #4548

Predictable traffic spike causes 503s

On-callReliability & on-callMid–Senior~30 min

A ticketing service has a known traffic pattern: every weekday at exactly 12:00 a popular daily on-sale opens and traffic spikes 5x within 60 seconds. Every day at 12:00 you get a 3-4 minute window of elevated p99 and some 503s, then it settles. Dashboards show CPU saturating right at 12:00, the HPA scaling up but new pods only becoming ready ~2-3 minutes later (image pull + app warmup), and the load balancer 503ing while pods are unready. No bug, no bad deploy — it's the same every day. Triage and propose durable mitigations.

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
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