A Deployment provides declarative updates for Pods and ReplicaSets.

You describe a desired state in a Deployment, and the Deployment Controller changes the actual state to the desired state at a controlled rate. You can define Deployments to create new ReplicaSets, or to remove existing Deployments and adopt all their resources with new Deployments.

Use Case

• Create a Deployment to rollout a ReplicaSet.
• Declare the new state of the Pods by updating the PodTemplateSpec of the Deployment. A new ReplicaSet is created and the Deployment manages moving the Pods from the old ReplicaSet to the new one at a controlled rate. Each new ReplicaSet updates the revision of the Deployment.
• Rollback to an earlier Deployment revision if the current state of the Deployment is not stable.
• Scale up the Deployment to facilitate more load.
• Pause the Deployment to apply multiple fixes to its PodTemplateSpec and then resume it to start a new rollout.
• Use the status of the Deployment as an indicator that a rollout has stuck.
• Clean up older ReplicaSets that you don't need anymore.

Creating a Deployment

The following is an example of a Deployment. It creates a ReplicaSet to bring up three nginx Pods.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80

• A Deployment named nginx-deployment is created, indicated by the .metadata.name field.
• The Deployment creates three replicated Pods, indicated by the .spec.replicas field.
• The .spec.selector field defines how the Deployment finds which Pods to manage. In this case, you simply select a label that is defined in the Pod template (app: nginx).
• The template field contains the following sub-fields:
  • The Pods are labeled app: nginx using the .metadata.labels field.
  • The Pod template's specification, or .template.spec field, indicates that the Pods run one container, nginx, which runs the nginx image at version 1.14.2.
  • Create one container and name it nginx using the .spec.template.spec.containers[0].name field.