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Autoscaling the Waste: Why Kubernetes Keeps Buying Capacity Your Applications Don’t Use

Blog post from Cast AI

Post Details
Company
Date Published
Author
Laurent Gil
Word Count
4,466
Company Posts That Month
21
Language
English
Hacker News Points
-
Post removed?
No
Summary

Kubernetes autoscaling can function as designed while clusters remain inefficient because controllers base decisions on declared resource requests, scheduling rules, and policies rather than actual application consumption. Cast AI’s 2026 report, covering an analyzed 2025 sample rather than all clusters, found average CPU and memory utilization of 8% and 20%, alongside reported CPU and memory overprovisioning of 69% and 79%, indicating frequent gaps between reserved and observed capacity but not directly equivalent bill savings. Oversized pod requests can cause extra nodes to be provisioned, while consolidation may be blocked by Pod Disruption Budgets, affinity and topology constraints, storage requirements, resource fragmentation, minimum node settings, controller policies, or long termination periods. Effective diagnosis requires tracing four layers—application consumption, resource requests, resource limits, and provisioned node capacity—and distinguishing overprovisioning from CPU throttling, since low average usage can conceal legitimate burst demand. Request changes must also be coordinated with Horizontal Pod Autoscaler settings because utilization-based HPA calculations divide consumption by requests, meaning reduced requests can trigger replica scale-outs. A cautious optimization process establishes baseline performance and cost-per-unit-of-work metrics, compares requests with usage, investigates scale-up and consolidation events, pilots coordinated workload and node changes, and verifies application reliability, capacity reductions, and billing effects, including the influence of committed cloud-spend arrangements.

Trends Found in this Post
Trend Post Mentions Total Month Mentions Posts Companies MoM
Kubernetes 15 956 75 30 -73%
Observability 2 472 102 54 -85%
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