Overview #

The PostFilter extension point was introduced in Kubernetes Scheduler since 1.19, and the default implementation in upstream is to preempt Pods on the same node to make room for the unschedulable Pod.

In contrast to the “same-node-preemption” strategy, we can come up with a “cross-node-preemption” strategy to preempt Pods across multiple nodes, which is useful when a Pod cannot be scheduled due to “cross node” constraints such as PodTopologySpread and PodAntiAffinity. This was also mentioned in the original design document of Preemption.

This plugin is built as a sample to demonstrate how to use PostFilter extension point, as well as inspiring users to built their own innovative strategies, such as preepmpting a group of Pods.

⚠️ CAVEAT: Current implementation doesn’t do any branch cutting, but uses a DFS algorithm to iterate all possible preemption strategies. DO NOT use it in your production env.

Maturity Level #

• 💡 Sample (for demonstrating and inspiring purpose)
• 👶 Alpha (used in companies for pilot projects)
• 👦 Beta (used in companies and developed actively)
• 👨 Stable (used in companies for production workloads)

Example config: #

apiVersion: kubescheduler.config.k8s.io/v1
kind: KubeSchedulerConfiguration
leaderElection:
  leaderElect: false
clientConnection:
  kubeconfig: "REPLACE_ME_WITH_KUBE_CONFIG_PATH"
profiles:
- schedulerName: default-scheduler
  plugins:
    postFilter:
      enabled:
      - name: CrossNodePreemption