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Defining a Zero-Downtime Deployment

Defining a Zero-Downtime Deployment

In this lesson, we will look into the definition of a zero-downtime deployment.

Updating a single-replica MongoDB cannot demonstrate true power behind Deployments. We need a scalable service. It’s not that MongoDB cannot be scaled (it can), but it is not as straight-forward as an application that was designed to be scalable. We’ll jump to the second application in the stack and create a Deployment of the ReplicaSet that will create Pods based on the vfarcic/go-demo-2 image.

Zero-downtime deployment is a prerequisite for higher frequency releases.

Looking into the Definition

Let’s take a look at the Deployment definition of the API.

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cat deploy/go-demo-2-api.yml

The output is as follows.

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apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: go-demo-2-api
spec:
  replicas: 3
  selector:
    matchLabels:
      type: api
      service: go-demo-2
  minReadySeconds: 1
  progressDeadlineSeconds: 60
  revisionHistoryLimit: 5
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 1
  template:
    metadata:
      labels:
        type: api
        service: go-demo-2
        language: go
    spec:
      containers:
      - name: api
        image: vfarcic/go-demo-2
        env:
        - name: DB
          value: go-demo-2-db
        readinessProbe:
          httpGet:
            path: /demo/hello
            port: 8080
          periodSeconds: 1
        livenessProbe:
          httpGet:
            path: /demo/hello
            port: 8080

We’ll skip explaining apiVersion, kind, and metadata, since they always follow the same pattern.

  • Line 5-7: The spec section has a few of the fields we haven’t seen before, and a few of those we are familiar with. The replicas and the selector are the same as what we used in the ReplicaSet from the previous chapter.

  • Line 11: minReadySeconds defines the minimum number of seconds before Kubernetes starts considering the Pods healthy. We put the value of this field to 1 second. The default value is ...

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