ReplicaSet (rs)

• ReplicaSet is a newer version of ReplicationController
• It uses selectors (just like services) to match the target pods by label
• ReplicaSet is a process that monitors the pods by their labels

Self healing

• ReplicaSet maintains a stable set of instances of a pod. It guarantees the availability of pods
• Therefore it is one of the pieces in Kubernetes that allows applications to self heal
• This helps in ensuring that a pod is re-created automatically when the application within the pod crashes
• Kubernetes provides additional support to check the health of applications running within PODs and take necessary actions through Liveness and Readiness Probes

Properties

spec.replicas

• The number of pods to run the app

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: my-rs
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      name: my-app-po
      labels:
        app: my-app
    spec:
      containers:
        - name: nginx-container
          image: nginx

spec.selector.matchLabels

• Select what pods will be replicated

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: my-rs
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      name: my-app-po
      labels:
        app: my-app
    spec:
      containers:
        - name: nginx-container
          image: nginx

spec.template

• The pod template to use to create new pods

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: my-rs
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      name: my-app-po
      labels:
        app: my-app
    spec:
      containers:
        - name: nginx-container
          image: nginx