Deployment (deploy)

• Deployment objects encapsulate ReplicaSet which encapsulates Pod
• Deployment objects create replicasets, which create pods automatically
• Enables rollout, rollbacks, rolling updates of pods
• Each new revision of the deployment creates a new replicaset, this way it is possible to rollback to previous versions

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-deploy
spec:
  replicas: 3 # target number of identical pod instances
  selector: # what pods to control
    matchLabels:
      app: myapp
  template: # single pod specification
    metadata:
      labels:
        app: myapp
    spec:
      containers:
        - name: nginx-container
          image: nginx

Properties

spec.strategy

• Deployment Strategy

• Recreate

• Destroy all replicas immediately and create new ones
• The old ReplicaSet is scaled down to 0 and the new ReplicaSet is scaled up to n

• It's good for databases that cannot have more than 1 replica at a time

• Rolling Update (default)

• Take down old version and bring up newer version one by one

• The old ReplicaSet is scaled down one at a time, simultaneously scaling up the new ReplicaSet one by one

• The final state of any deployment strategies maintains the newer ReplicaSet (scaled to N), and the older ReplicaSet (scaled to 0)

• The reason to maintain the older ReplicaSet is for rolling back purposes

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deploy
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
        - name: nginx
          image: nginx
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 25%
      maxUnavailable: 25% # max 25% will go down at once to upgrade

spec.minReadySeconds

• Readiness

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deploy
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
        - name: nginx
          image: nginx
  minReadySeconds: 15

spec.revisionHistoryLimit

• My default, a deployment maintains the history of the last 10 revisions

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deploy
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
        - name: nginx
          image: nginx
  revisionHistoryLimit: 15

spec.replicas (bypass)

• Bypass to rs.spec.replicas

spec.selector (bypass)

• Bypass to rs.spec.selector

spec.template (bypass)

• Bypass to rs.spec.template