CASE 17 · COBALT · 2025
Karpenter, Spot, and the EKS bill that fell sixty percent.
An AdTech company ran 14 EKS clusters with Cluster Autoscaler, a fixed set of node groups, and an on-demand-only policy. The compute bill was $180k/month and the autoscaler routinely ran clusters at 38% utilisation. We replaced it with Karpenter, opened the cluster to Spot, and pulled utilisation past 70%.
AdTech
COST
2025
RESULTS
What changed, by the numbers.
COMPUTE BILL
−60%
CLUSTER UTILISATION
72%
SPOT INTERRUPTIONS
< 0.1%
PROVISIONING TIME
−83%
HOW IT WENT
Cluster Autoscaler was making over-conservative choices because the node groups were over-specified. Every workload had a `nodeSelector`. Every node group was sized for the heaviest workload that might land on it. Nobody had touched the limit ranges in a year.
Karpenter replaced both the autoscaler and the per-node-group thinking. We let it choose instance types from a pool of seventeen families (mix of x86 and Graviton), with constraints on architecture only where the workload required it. Spot was enabled with capacity-optimized allocation strategy and pod disruption budgets sized per workload.
Interruption rate landed at 0.07% of pod-minutes — well within the noise floor for the workloads. Goldilocks recommendations tightened pod resource requests in the second month, freeing more headroom. The 60% bill reduction is now the team’s most-cited slide in their internal architecture reviews.
RELATED · SAME DOMAIN
Other engagements in this space.
READY WHEN YOU ARE
Let's get your AWS bill (and architecture) in order.
The discovery call is free. You walk away with at least one concrete idea — even if we never work together.