Select Node

Taints and Tolerations

• If a node is tainted, only the pod which has required toleration can be scheduled on this node.
• Master node is tainted so that no pod can be scheduled on it.

Taint

• Object: node
• Key workds:
  • key, e.g., app
  • value, e.g., myweb
  • taint effect
    • 1. Noschedule: a pod will not be scheduled on the tainted node.
    • 1. PreferNoSchedule: k8s will try to avoid to schedule a pod on a node but it is not guartenteed.
    • 1. NoExecute: new pods will not be scheduled on the node, and for what has been scheduled on the node will be removed.
• command:
  • Format: kubectl taint nodes <node_name> key=value:taint-effect
  • Example: kubectl taint nodes mynode app=myweb:NoExecute

Toleration

• Object: pod
• key words:
• yaml: e.g., pod.yaml

  apiVersion: v1
  kind: Pod
  metadata:
    name: myapp
  spec:
    containers:
      name: myapp
       
    tolerations:
    - key: "app" 
      operator: "Equal"
      value: "taintedNode" 
      effect: "NoSchedule"
  

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Node Selectors

• Make a pod be scheduled on a specific node.

• Label a Node:
  • Command line:
    • Format: kubectl label nodes <node_name> <label_key>=<label_value>
    • Example: kubectl label nodes mynode size=small
• Selcet the Node by label: ```yaml apiVersion: v1 kind: Pod metadata: name: myapp spec: containers:
  • name: mycontainer image: mycontainer nodeSelector: size: small ```
• If you want to select nodes in a more comlicated situation, use affinity instead.

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Affinity

• To ensure a pod to be scheduled on a specific node.

Types

• Available:
  • requiredDuringSchedulingIgnoredDuringExecution
  • peferredDuringSchedulingIgnoredDuringExecution
• Planned:
  • requiredDuringSchedulingRequiredDuringExecution

apiVersion: v1
kind: Pod
metadata:
  name: myapp
spec:
  containers:
  - name: mycontainer
    image: mycontainer
  affinity:
    nodeAffinity:
      requiredDuringSchedulingIgnoreDuringExecution:
        nodeSelectorTrems:
        - matchExpressions:
          - key: size
            operator: In
            values:
            - Small