What are taints and tolerations? How are they used?

Taints and tolerations are mechanisms in Kubernetes that allow controlling on which nodes pods can be scheduled.

• Taints are labels applied to nodes that prevent pods from being scheduled on them unless the pod has a matching toleration. This is a way to say: "This node is not suitable for regular pods, only for those that "tolerate" this taint."

• Tolerations are properties of a pod that allow it to "tolerate" (ignore) taints on nodes and be scheduled on them.

Example of usage:

If you have a node with a taint key=value:NoSchedule, then regular pods will not be scheduled on it unless they have a toleration with the same key and value.

apiVersion: v1
kind: Pod
metadata:
  name: tolerant-pod
spec:
  tolerations:
  - key: "key"
    operator: "Equal"
    value: "value"
    effect: "NoSchedule"
  containers:
  - name: app
    image: nginx

Thus, taints and tolerations help isolate nodes for special tasks, such as nodes with specific resources or to prevent pods from running on problematic nodes.