As discussed earlier, replica sets are the new and improved version of replication controllers. Here's a basic example of their functionality, which we'll expand further in Chapter 4, Implementing Reliable Container-Native Applications, with advanced concepts.
Here is an example of ReplicaSet based on and similar to the ReplicationController. Name this file as nodejs-labels-replicaset.yaml:

apiVersion: extensions/v1beta1 
kind: ReplicaSet 
metadata: 
  name: node-js-rs 
spec: 
  replicas: 3 
  selector: 
    matchLabels: 
      app: node-js-express 
      deployment: test 
    matchExpressions: 
      - {key: name, operator: In, values: [node-js-rs]} 
  template: 
    metadata: 
      labels: 
        name: node-js-rs 
        app: node-js-express 
        deployment: test 
    spec: 
      containers: 
      - name: node-js-rs 
        image: jonbaier/node-express-info:latest 
        ports: 
        - containerPort: 80