Kubernetes - Deployments 🚀

Description 👀

Deployments are the preferred way to manage pods. They are a higher level abstraction thanReplica Sets. They allow you to define the desired state of your application, and the controller will make sure that the current state matches the desired state.

Updates and Rollbacks 🔄

• Deployments allow you to update your application without downtime.

• There are two methods to update your application:

  • Rolling Update - The new version of the application is deployed in stages. The old version is still running while the new version is being deployed. Once the new version is deployed, the old version is terminated.

  • Recreate - The old version of the application is terminated before the new version is deployed.

• rollbacks are also possible. You can rollback to a previous version of your application.

Basic Commands 📝

• update a deployment   (rolling update)

  kubectl apply -f <yaml-file>
  

  kubectl set image deployment/<deployment-name> <new-image>
  

• get list of deployments

  kubectl get deployments
  

• get descriptive information on the desired deployment

  kubectl describe deployment <deployment-name>
  

• get the rollout status of the deployment

  kubectl rollout status deployment/<deployment-name>
  

• get the rollout history of the deployment

  kubectl rollout history deployment/<deployment-name>
  

• rollback to a previous version of the deployment

  kubectl rollout undo deployment/<deployment-name>
  

• use the --to-revision flag to specify the revision number to rollback to.

  kubectl rollout undo deployment/<deployment-name> --to-revision=<revision-number>
  

• view deployment at a specific revision

  kubectl rollout history deployment <deployment-name> --revision=<revision-number>
  

• use the --record flag to save the command used to create/update a deployment

  kubectl apply -f <yaml-file> --record=true
  

Examples 🧩

• sample deployment definition

  apiVersion: apps/v1
  kind: Deployment
  metadata:
    name: myapp-depl
    labels:
      tier: front-end
  spec: 
    template:
      metadata:
        name: nginx-pod
        labels:
          app: myapp
          type: front-end
      spec:
        containers:
          - name: nginx
            image: nginx
    replicas: 6
    selector: 
      matchLabels:
        app: myapp
  

• sample deployment definition with web-hook
  • sample service definition is in the core-concepts/services section
  • sample tls secret is in the configuration/secrets section

  apiVersion: apps/v1
  kind: Deployment
  metadata:
    name: webhook-server
    namespace: webhook-demo
    labels:
      app: webhook-server
  spec:
    replicas: 1
    selector:
      matchLabels:
        app: webhook-server
    template:
      metadata:
        labels:
          app: webhook-server
      spec:
        securityContext:
          runAsNonRoot: true
          runAsUser: 1234
        containers:
        - name: server
          image: stackrox/admission-controller-webhook-demo:latest
          imagePullPolicy: Always
          ports:
          - containerPort: 8443
            name: webhook-api
          volumeMounts:
          - name: webhook-tls-certs
            mountPath: /run/secrets/tls
            readOnly: true
        volumes:
        - name: webhook-tls-certs
          secret:
            secretName: webhook-server-tls
  

• sample web-hook definition for deployment

  apiVersion: admissionregistration.k8s.io/v1
  kind: MutatingWebhookConfiguration
  metadata:
    name: demo-webhook
  webhooks:
    - name: webhook-server.webhook-demo.svc
      clientConfig:
        service:
          name: webhook-server
          namespace: webhook-demo
          path: "/mutate"
        caBundle: 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
      rules:
        - operations: [ "CREATE" ]
          apiGroups: [""]
          apiVersions: ["v1"]
          resources: ["pods"]
      admissionReviewVersions: ["v1beta1"]
      sideEffects: None
  

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