Mastering Node-Pressure Eviction in Kubernetes

Node-pressure eviction exists to prevent resource starvation in your Kubernetes cluster. When nodes run low on critical resources like memory or disk space, the kubelet steps in to terminate pods proactively. This mechanism ensures that your applications remain responsive and that the cluster operates smoothly, even under heavy load.

The kubelet continuously monitors resource usage on nodes. It uses eviction signals to determine when to act. If memory usage exceeds defined thresholds—like memory.available<1Gi—the kubelet will fail selected pods, setting their phase to Failed. You can configure soft and hard eviction thresholds. Soft thresholds allow for a grace period, while hard thresholds trigger immediate termination. For example, you might set memory.available<10% as a hard threshold to ensure that memory availability never drops too low.

In production, understanding the nuances of node-pressure eviction is essential. The kubelet does not respect PodDisruptionBudgets during these evictions, which can lead to unexpected behavior if you rely on them for availability. Be aware that the CommitLimit can change based on the node's page-file size, which might affect your eviction strategy. As of Kubernetes v1.31, this feature is enabled by default, but ensure you’re aware of version-specific requirements, like enabling the KubeletSeparateDiskGC feature gate in v1.35.