Overview
The Cluster Autoscaler (CA) ensures that the cluster has enough nodes to run all scheduled Pods and removes underutilized nodes to save costs. It works by interacting with the underlying cloud provider's infrastructure (e.g., AWS Auto Scaling Groups, Google Cloud Managed Instance Groups).
When it Scales Up
When there are Pods that failed to run in the cluster due to insufficient resources (unschedulable Pods).
When it Scales Down
When a node has been underutilized for a significant period and its Pods can be moved to other existing nodes.
Importance
CA is essential for running cost-effective and highly available clusters in the cloud, especially when combined with HPA.