How Karpenter Replaces Cluster Autoscaler on AWS EKS Using Terraform

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Karpenter is an open-source Kubernetes node provisioner that replaces traditional Cluster Autoscaler by directly calling the AWS EC2 Fleet API to launch right-sized instances whenever pods cannot be scheduled. Unlike Cluster Autoscaler, which relies on pre-configured Auto Scaling Groups with fixed instance types, Karpenter evaluates each pending pod's actual resource requirements and selects the most cost-effective EC2 instance available. This approach typically brings new nodes online within a minute and supports automatic consolidation, shutting down underutilized nodes by bin-packing workloads onto existing capacity. Teams adopting Karpenter can reduce costs significantly by mixing Spot and On-Demand instances, allowing broad instance family selection, and enabling scheduled node expiry for automatic patching. A Terraform-based setup requires an existing EKS cluster, VPC, subnets, security groups, and tools including Helm, kubectl, and the AWS CLI.

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