Kubernetes - Imperative Commands 🧙

Description 👀

Imperative commands can help in getting one time tasks done quickly, as well as generate a definition template easily.

Familiarize yourself with the following commands

• --dry-run
  • will execute, and the resource will be created.
• --dry-run=client
  • will execute, but the resource will not be created.
• -o yaml
  • will output the resource definition in yaml format.

Basic Commands 📝

Use in combination to generate a resource definition file quickly, that you can then modify and create resources as required, instead of creating the files from scratch.

• create a pod definition

    kubectl run <pod-name> --image=<image-name> --dry-run=client -o yaml
  

• create a deployment definition

    kubectl create deployment --image=<image-name> --dry-run=client -o yaml
  

• create a service definition

    kubectl expose <object-type> <object-name> --port=<port> --name <service-name> --dry-run=client -o yaml
  

Examples 🧩

• create a service named nginx of type NodePort to expose pod nginx’s port 80 on port 30080 on the nodes

    kubectl expose pod nginx --port=80 --name nginx-service --type=NodePort --dry-run=client -o yaml
  

  This will automatically use the pod’s labels as selectors, but you cannot specify the node port. You have to generate a definition file and then add the node port in manually before creating the service with the pod.

• deploy a redis pod using the redis:alpine image with the labels set to tier=db.

    kubectl run redis --image=redis:alpine --labels="tier=db" --dry-run=client -o yaml > redis-pod.yaml
  

  • output

    apiVersion: v1
    kind: Pod
    metadata:
        creationTimestamp: null
        labels:
            tier: db
        name: redis
    spec:
        containers:
          - image: redis:alpine
            name: redis
            resources: {}
        dnsPolicy: ClusterFirst
        restartPolicy: Always
        status: {}
    

• create a service redis-service to expose the redis application within the cluster on port 6379

    kubectl expose pod redis --port=6379 --name=redis-service --type=ClusterIP --dry-run=client -o yaml > redis-service.yaml 
  

• create a deployment named webapp using the image kodekloud/webapp-color with three replicas

    kubectl create deployment webapp --image=kodekloud/webapp-color --replicas=3 --dry-run=client -o yaml > webapp-dep.yaml
  

• create a pod using nginx with container port 8080 exposed

    kubectl run custom-nginx --image=nginx --port=8080
  

• create a new deployment called redis-deploy in the dev-ns namespace with the redis image, it should have two replicas

    kubectl -n dev-ns create deployment redis-deploy --image=redis --replicas=2 --dry-run=client -o yaml > rd-dev.yaml
  

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