Kubernetes Scheduling Controls

By default, the Kubernetes scheduler tries to balance Pods across nodes. However, you often need to override this behavior for performance, security, or infrastructure reasons.

1. Taints and Tolerations

• Taints: Applied to Nodes. They allow a node to “repel” a set of pods. A taint has a key, value, and effect (e.g., NoSchedule).
• Tolerations: Applied to Pods. They allow (but do not require) the pod to schedule onto nodes with matching taints.
• Use Case: Dedicating nodes to a specific team or specialized hardware (like GPUs).

2. Node Affinity

• Definition: Applied to Pods. It is a set of rules used by the scheduler to determine where a pod can be placed, based on labels on the node.
• Types:
  • requiredDuringSchedulingIgnoredDuringExecution: Hard requirement (must match).
  • preferredDuringSchedulingIgnoredDuringExecution: Soft requirement (try to match).
• Use Case: Ensuring a Pod runs on a node with an SSD or in a specific Availability Zone.

3. Pod Affinity and Anti-Affinity

• Affinity: Keep related Pods together on the same node (e.g., an app and its cache) to reduce latency.
• Anti-Affinity: Keep Pods apart (e.g., don’t put two replicas of the same DB on the same node) to ensure high availability.

Summary Comparison