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47. Use Karpenter For Scaling

Date: 2026-04-21

Status

✅ Accepted

Context

The Cloud Platform Team investigated Karpenter as the technology solution for scaling during the build of Container Platform. We installed and tested Karpenter. We compared Karpenter with Cluster Auto Scaler and EKS Auto Mode. Testing was successful.

Testing was carried out on Modernisation Platform running on AWS. It is assumed the cloud provider being used for Container Platform will continue to be AWS.

Decision

We will use Karpenter as the primary scaling solution for Container Platform.

Consequences

  • Scaling is event-driven via direct EC2 Fleet API calls
  • User workloads will not run in node groups (Karpenter runs outside of node groups, picking instance types dynamically)
  • Scaling should occur faster than in Cloud Platform
  • Node consolidation is more aggressive
  • We need to come up with a list of acceptable AWS Instance types and limit to that
  • We need to perform tuning and testing with Karpetner
  • We need to ensure security - see Karpenter Threat Model
  • Although it's not our primary use-case Cluster Auto Scaler could still run alongside Karpenter if needed