Edit a kubernetes (k8s) deployment

So when you create a real world deployment, you eventually will have to modify it, whether that means you're just updating the image artifact with a new deploy. Or maybe you need to tweak the number of replicas, add cpu/memory limits, etc. So you can either update the yaml file you ran kubectl apply -f <XYZ.yaml> on, or you can just run kubectl edit deployment <mydeployment> and it will pop open your default editor for you to be able to modify the deployment in real time.

In our case we're going to modify the hello-minikube deployment we have. Run the following command, and it will open up your default editor, on linux this will typically be vi/vim

PS ...\kubernetes\kubernetesTraining> kubectl edit deployment hello-minikube       

Here is the output when you're inside your editor.

kind: Deployment
metadata:
  annotations:
    deployment.kubernetes.io/revision: "3"
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"apps/v1","kind":"Deployment","metadata":{"annotations":{},"labels":{"app":"hello-minikube"},"name":"hello-minikube","namespace":"default"},"spec":{"progressDeadlineSeconds":600,"replicas":3,"revisionHistoryLimit":10,"selector":{"matchLabels":{"app":"hello-minikube"}},"strategy":{"rollingUpdate":{"maxSurge":"25%","maxUnavailable":"25%"},"type":"RollingUpdate"},"template":{"metadata":{"creationTimestamp":null,"labels":{"app":"hello-minikube"}},"spec":{"containers":[{"image":"k8s.gcr.io/echoserver:1.10","imagePullPolicy":"IfNotPresent","name":"echoserver","resources":{},"terminationMessagePath":"/dev/termination-log","terminationMessagePolicy":"File"}],"dnsPolicy":"ClusterFirst","restartPolicy":"Always","schedulerName":"default-scheduler","securityContext":{},"terminationGracePeriodSeconds":30}}}}
  creationTimestamp: "2020-02-23T14:33:11Z"
  generation: 6
  labels:
    app: hello-minikube
  name: hello-minikube
  namespace: default
  resourceVersion: "235503"
  selfLink: /apis/apps/v1/namespaces/default/deployments/hello-minikube
  uid: 08a2d4f6-5346-4d13-9a44-3b7a0fb7dc44
spec:
  progressDeadlineSeconds: 600
  replicas: 3
  revisionHistoryLimit: 10
  selector:
    matchLabels:
      app: hello-minikube
  strategy:
    rollingUpdate:
      maxSurge: 25%
      maxUnavailable: 25%
    type: RollingUpdate
  template:
    metadata:
      creationTimestamp: null
      labels:
        app: hello-minikube
    spec:
      containers:
      - image: k8s.gcr.io/echoserver:1.10
        imagePullPolicy: IfNotPresent
        name: echoserver
        resources: {}
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File
      dnsPolicy: ClusterFirst
      restartPolicy: Always
      schedulerName: default-scheduler
      securityContext: {}
      terminationGracePeriodSeconds: 30
status:
  availableReplicas: 3
  conditions:
  - lastTransitionTime: "2020-02-23T14:33:11Z"
    lastUpdateTime: "2020-02-23T14:48:52Z"
    message: ReplicaSet "hello-minikube-797f975945" has successfully progressed.
    reason: NewReplicaSetAvailable
    status: "True"
    type: Progressing
  - lastTransitionTime: "2020-02-23T15:16:44Z"
    lastUpdateTime: "2020-02-23T15:16:44Z"
    message: Deployment has minimum availability.
    reason: MinimumReplicasAvailable
    status: "True"
    type: Available
  observedGeneration: 6
  readyReplicas: 3
  replicas: 3
  updatedReplicas: 3

Lets go in and change the number of replicas from 3 -> 1 find the line

replicas: 3 and change the 3 to a 1, then save and exit the file, and you'll get a prompt that the deployment has been edited.

PS ...\kubernetes\kubernetesTraining> kubectl edit deployment hello-minikube       deployment.apps/hello-minikube edited

Now lets verify that our changes to the replica count were committed properly.

PS ...\kubernetes\kubernetesTraining> kubectl get deployment hello-minikube -o yaml | grep -i replicas                                                                                         {"apiVersion":"apps/v1","kind":"Deployment","metadata":{"annotations":{},"labels":{"app":"hello-minikube"},"name":"hello-minikube","namespace":"default"},"spec":{"progressDeadlineSeconds":600,"replicas":3,"revisionHistoryLimit":10,"selector":{"matchLabels":{"app":"hello-minikube"}},"strategy":{"rollingUpdate":{"maxSurge":"25%","maxUnavailable":"25%"},"type":"RollingUpdate"},"template":{"metadata":{"creationTimestamp":null,"labels":{"app":"hello-minikube"}},"spec":{"containers":[{"image":"k8s.gcr.io/echoserver:1.10","imagePullPolicy":"IfNotPresent","name":"echoserver","resources":{},"terminationMessagePath":"/dev/termination-log","terminationMessagePolicy":"File"}],"dnsPolicy":"ClusterFirst","restartPolicy":"Always","schedulerName":"default-scheduler","securityContext":{},"terminationGracePeriodSeconds":30}}}}
  replicas: 1
  availableReplicas: 1
    message: ReplicaSet "hello-minikube-797f975945" has successfully progressed.
    reason: NewReplicaSetAvailable
    reason: MinimumReplicasAvailable
  readyReplicas: 1
  replicas: 1
  updatedReplicas: 1

We can see by greping the current deployment as yaml and grepping for replica that the replicas did in fact update from 3 to 1.

You can use this syntax and style for any kubernetes (k8s) changes you want to do in real time.