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Creating ReplicaSets

Creating ReplicaSets

In this lesson, first, we will create a ReplicaSet and then retrieve it.

Looking into the Definition

Let’s take a look at a ReplicaSet based on the Pod we created in the previous chapter.

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cat rs/go-demo-2.yml

The output is as follows.

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apiVersion: apps/v1beta2
kind: ReplicaSet
metadata:
  name: go-demo-2
spec:
  replicas: 2
  selector:
    matchLabels:
      type: backend
      service: go-demo-2
  template:
    metadata:
      labels:
        type: backend
        service: go-demo-2
        db: mongo
        language: go
    spec:
      containers:
      - name: db
        image: mongo:3.3
      - name: api
        image: vfarcic/go-demo-2
        env:
        - name: DB
          value: localhost
        livenessProbe:
          httpGet:
            path: /demo/hello
            port: 8080

The apiVersion, kind, and metadata fields are mandatory with all Kubernetes objects. ReplicaSet is no exception, i.e., it is also a Kubernetes object.

  • Line 1: We specified that the apiVersion is apps/v1beta2. At the time of this writing, ReplicaSet is still in beta. Soon it will be considered stable, and you’ll be able to replace the value with apps/v1.

  • Line 2-3: The kind is ReplicaSet and metadata has the name key set to go-demo-2. We could have extended ReplicaSet metadata with labels. However, we skipped that part since they would serve only for informational purposes. They do not affect the behavior of the ReplicaSet.

You should be familiar with the above three fields since we already explored them when we worked with Pods. In addition to them, the spec section is mandatory as well.

  • Line 5-6: The first ...

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