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We Had HPA, VPA, and Still Got Paged During the Diwali Sale Spike

Learn when to reach for HPA, VPA, or event-driven scaling so your pods react to real traffic instead of average CPU.

MCB Editorial

Tech Buzz Daily Desk · 10 min read ·

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Learning Objectives & Key Takeaways

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What you will learn
  1. HPA changes replica count based on metrics like CPU, memory, or external signals through autoscaling/v2.
  2. VPA changes CPU and memory requests on existing pods and needs Metrics Server plus its own add-on install.
  3. HPA and VPA solve different problems and can conflict if both manage CPU-based requests on the same workload.
  4. Scale-to-zero with HorizontalPodAutoscaler needs minReplicas 0 and a metric that stays visible while the workload is idle.
  5. Event-driven scaling for queues and streams is a distinct pattern from CPU-based HPA, even when the exact tool details need verifying against current docs.

The Sale That Broke Our Assumptions

Our checkout service had an HorizontalPodAutoscaler capped at ten replicas, and on a normal day that felt generous. During the Diwali flash sale, traffic tripled in eleven minutes and the HPA dutifully scaled us to the maxReplicas ceiling, yet checkout latency kept climbing.

The replicas were there, but each pod was still starved because its CPU request was sized for average traffic from six months earlier. We were watching the right dashboard for the wrong signal, replica count looked healthy while the actual bottleneck was per-pod resource sizing.

In the rest of this story
  1. Three Dials, Not One
  2. Wiring HPA for Real Traffic, Including Scale to Zero
  3. Letting VPA Fix the Sizing Problem HPA Can't Touch
  4. Where Event-Driven Scaling Fits, Carefully
  5. The Production Checklist We Wish We Had Before the Sale
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MCB Editorial

Tech Buzz Daily Desk. Contributing deep-dive engineering architectures, cloud paradigms, and system design insights to Master Class Buddy.