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ReplicaSets

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  • The ReplicaSet ensures that the specified number of pods is always running.
  • For example: If we specify the number of pods as 3 for a ReplicaSet, then at any given point, the number of pods running will be 3.
  • If there are more than 3 pods, the ReplicaSet will terminate the extra pods, and if there are fewer than 3 pods, the ReplicaSet will start new pods.
  • In short, the pods are now maintained by the ReplicaSet. It will automatically replace pods that are unhealthy.
apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: server
  labels:
    app: webserver
    env: prod
spec:
  replicas: 3
  selector:
    matchLabels:
      env: prod
  template:
    metadata:
      labels:
        env: prod
    spec:
      containers:
      - name: nginx
        image: nginx
  • The .spec is the section where you define the desired state for the ReplicaSet object. It consist of replicas, selector, and template (pod template). This all are mandatory fields
  • The .spec.replicas is a field that specifies the desired number of pod you want to run at any given time.
  • The .spec.selector is a label selector which tells the ReplicaSet how to find which Pods it should manage.
  • The .spec.template is a pod template that ReplicaSet will manage.
  • The .spec.template.metadata.labels are the labels given to the pod which will be manage/created by this ReplicaSet. This is crucial as ReplicaSet will manages all the pods with labels that match the selector and hence .spec.template.metadata.labels must be equal to the .spec.selector. See Labels And Selectors

⬅️ Pod | Deployment ➡️

References

  1. https://kubernetes.io/docs/concepts/workloads/controllers/replicaset/

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