Creating a Deployment

A Deployment is a higher level abstraction which sits on top of replica sets and allows you to manage the way applications are deployed, rolled back at a controlled rate.

Deployment has mainly two responsibilities,

• Provide Fault Tolerance: Maintain the number of replicas for a type of service/app. Schedule/delete pods to meet the desired count.
• Update Strategy: Define a release strategy and update the pods accordingly.

/k8s-code/projects/instavote/dev/
cp vote-rs.yaml vote-deploy.yaml

Deployment spec (deployment.spec) contains everything that replica set has + strategy. Lets add it as follows,

File: vote-deploy.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: vote
spec:
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 2
      maxUnavailable: 1
  revisionHistoryLimit: 4
  paused: false
  replicas: 8
  minReadySeconds: 20
  selector:
    matchLabels:
      role: vote
    matchExpressions:
      - {key: version, operator: In, values: [v1, v2, v3]}
  template:
    metadata:
      name: vote
      labels:
        app: python
        role: vote
        version: v2
    spec:
      containers:
        - name: app
          image: schoolofdevops/vote:v2
          ports:
            - containerPort: 80
              protocol: TCP

This time, start monitoring with --show-labels options added.

watch -n 1 kubectl get  pod,deploy,rs,svc --show-labels

Lets create the Deployment. Do monitor the labels of the pod while applying this.

kubectl apply -f vote-deploy.yaml

Observe the chances to pod labels, specifically the pod-template-hash.

Now that the deployment is created. To validate,

kubectl get deployment
kubectl get rs --show-labels
kubectl get deploy,pods,rs
kubectl rollout status deployment/vote
kubectl get pods --show-labels

Sample Output

kubectl get deployments
NAME       DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
vote   3         3         3            1           3m

Scaling a deployment

To scale a deployment in Kubernetes:

kubectl scale deployment/vote --replicas=12

kubectl rollout status deployment/vote

Sample output:

Waiting for rollout to finish: 5 of 12 updated replicas are available...
Waiting for rollout to finish: 6 of 12 updated replicas are available...
deployment "vote" successfully rolled out

You could also update the deployment by editing it.

kubectl edit deploy/vote

[change replicas to 15 from the editor, save and observe]

Rolling Updates in Action

Now, update the deployment spec to apply

file: vote-deploy.yaml

spec:
...
  replicas: 15
...
labels:
   app: python
   role: vote
   version: v3
...
template:   
  spec:
    containers:
      - name: app
        image: schoolofdevops/vote:v3

apply

kubectl apply -f vote-deploy.yaml

kubectl rollout status deployment/vote

Observe rollout status and monitoring screen.

kubectl rollout history deploy/vote

kubectl rollout history deploy/vote --revision=1

Undo and Rollback

file: vote-deploy.yaml

spec:
  containers:
    - name: app
      image: schoolofdevops/vote:rgjerdf

apply

kubectl apply -f vote-deploy.yaml

kubectl rollout status

kubectl rollout history deploy/vote

kubectl rollout history deploy/vote --revision=xx

where replace xxx with revisions

Find out the previous revision with sane configs.

To undo to a sane version (for example revision 3)

kubectl rollout undo deploy/vote --to-revision=3