Kubernetes - Deployment [Part 9]

 

TDeployments are declarative objects that described the deployed application. The Deployment object exists to manage the release of new version of the applications. We can simply to rollout or rollback without downtime through deployment.

The Yaml file for the deployment:

apiVersion: extensions/v1beta1

kind: Deployment

metadata:

  name: kuard

spec:

  selector:

    matchLabels:

      run: kuard

  replicas: 1

  template:

    metadata:

      labels:

        run: kuard

    spec:

      containers:

      - name: kuard

        image: gcr.io/kuar-demo/kuard-amd64:blue

The ReplicaSet is managing the Pods and Deployment is managing the ReplicaSet.

We can get know the ReplicaSet and desire status from the Deployment.

#kubectl get deployments deploymentname -o jsonpath --template {.spec.selector.matchLabels}

Example:

$ kubectl get deployments kuard -o jsonpath --template {.spec.selector.matchLabels}

map[run:kuard]

$ kubectl get replicasets --selector=run=kuard

NAME              DESIRED   CURRENT   READY     AGE

kuard-1128242161  1         1         1         13m

The Yaml file for the rolling update through deployment:

apiVersion: extensions/v1beta1

kind: Deployment

metadata:

  annotations:

    deployment.kubernetes.io/revision: "1"

  creationTimestamp: null

  generation: 1

  labels:

    run: kuard

  name: kuard

  selfLink: /apis/extensions/v1beta1/namespaces/default/deployments/kuard

spec:

  progressDeadlineSeconds: 2147483647

  replicas: 2

  revisionHistoryLimit: 10

  selector:

    matchLabels:

      run: kuard

  strategy:

    rollingUpdate:

      maxSurge: 1

      maxUnavailable: 1

    type: RollingUpdate

  template:

    metadata:

      creationTimestamp: null

      labels:

        run: kuard

    spec:

      containers:

      - image: gcr.io/kuar-demo/kuard-amd64:blue

        imagePullPolicy: IfNotPresent

        name: kuard

        resources: {}

        terminationMessagePath: /dev/termination-log

        terminationMessagePolicy: File

      dnsPolicy: ClusterFirst

      restartPolicy: Always

      schedulerName: default-scheduler

      securityContext: {}

      terminationGracePeriodSeconds: 30

status: {}

The Strategy object is defined the rollout option of the deployment. It has two ways to do this rollout task. 1) recreate 2) RollingUpdate

The deployment is using for two main purposes. 1) Scaling 2) Rolling update

Scaling:

We can edit the deployment yaml file updated the ReplicaSet as per your scaling. We can autoscaling easily without any downtime through deployment.

Rolling update or updated with Latest image:

We can edit the yaml file and updated the latest image of the application. It will rollout without any error/downtime through deployment.

P.S: Make sure to add the change cause annotation whenever your performing the rolling out of the application.

Monitoring the Rollout action:

# kubectl rollout status deployments deploymentname

Example:

$ kubectl rollout status deployments kuard

deployment kuard successfully rolled out

Rollout history:

#kubectl rollout history deployments deploymentname

Rollback the deployment to previous version incase of any issue with new release.

# kubectl rollout undo deployments deploymentname

$ kubectl rollout undo deployments kuard

deployment "kuard" rolled back

DameonSet:

DamonSet are used to deploying a system dameons such as log collectors and monitoring agents which typically run on each nodes. DamonSets are created by submitting a DemonSet configuration to the Kubernetes API server. 

The Yaml file for the DameonSet:

apiVersion: extensions/v1beta1

kind: DaemonSet

metadata:

  name: fluentd

  labels:

    app: fluentd

spec:

  template:

    metadata:

      labels:

        app: fluentd

    spec:

      containers:

      - name: fluentd

        image: fluent/fluentd:v0.14.10

        resources:

          limits:

            memory: 200Mi

          requests:

            cpu: 100m

            memory: 200Mi

        volumeMounts:

        - name: varlog

          mountPath: /var/log

        - name: varlibdockercontainers

          mountPath: /var/lib/docker/containers

          readOnly: true

      terminationGracePeriodSeconds: 30

      volumes:

      - name: varlog

        hostPath:

          path: /var/log

      - name: varlibdockercontainers

        hostPath:

          path: /var/lib/docker/containers

Node selectors can be limit what pods can run on given time in the K8S cluster. It will restrict the Pod creation on every node by using a DamonSet configuration.