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Kubectl CLI

All of these commands send requests to the Kubernetes API

Tips

  • For any command, you can specify which namespace to use with the -n flag.
    • ex. kubectl get pod -n <namespace>
    • By default, the default namespace will be used.
  • Instead of passing the identifier of the actual Kubernetes object, we can pass the yaml config file with the -f flag
    • ex. kubectl describe -f <config>.yml
  • run shell command in a pod - kubectl exec -it -- <podname>
    • open a bash shell in pod - kubectl exec -it <podname> bash
    • list processes - kubectl exec <podname> -- ps aux
    • list env variables - kubectl exec <podname> env
  • pass -c <containername> to specify which container to run the process in.

Read

Config

kubectl config current-context

  • see where kubectl is pointing

kubectl config view

  • show (redacted) contents of ~/.kube/config

Describe

  • give information on a resource (aka Kubernetes object) kubectl describe pod <podname>

Get

kubectl get pods

  • get all pods of a cluster
  • pass -o wide or -o yaml for more info
  • --show-labels to see the labels on each pod

kubectl get namespaces

kubectl get all --all-namespace kubectl get all --all-namespacess

  • get all components that make up the cluster

kubectl get nodes

  • get all nodes of a cluster

kubectl get rs

  • get all ReplicaSets

kubectl get ep

  • get endpoints of a cluster

kubectl get -f pod/go-demo-2.yml -o jsonpath="{.spec.containers[*].name}"

  • format output as only including the name property, within spec.containers

Logs

  • get logs from a pod kubectl logs <podname>
  • -f to follow the logs in real-time

Context

kubectl config get-contexts

  • get clusters

kubectl config use-context <CLUSTER-NAME>

  • switch cluster

Create/Update

Apply

kubectl apply -f rs/rs.yml

  • apply a configuration to a resource.
  • we can create resources with this command, by applying to a resource that doesn't exist.
    • we can also create with --save-config

Create

kubectl create -f pod/db.yml

  • create a pod based on the db.yml file
  • note: we didn't need to specify that we were creating a pod, since the resource type is already defined in the yml file (kind field).
  • --record allows us to track each change to our resources such as a Deployments.

Destroy

Delete

kubectl delete pod <podname>

  • delete a pod

kubectl delete namespace <namespace>

  • delete a namespace

Expose

  • expose a resource as a new Kubernetes service 
    - the resource can be a Deployment, another Service, a ReplicaSet, a ReplicationController, or a Pod
    ex
kubectl expose rs go-demo-2 \
	--name=go-demo-2-svc \
	# this port will be exposed on every node of the cluster to the outside world,
	# and it will be routed to one of the Pods controlled by the ReplicaSet
	--target-port=28017 \
	--type=NodePort # what type of service?

Label

  • We can remove a label from a pod:
    • kubectl label pod/pod.yml service- will remove the service label (the - at the end is the syntax for removing labels)

Rollout

  • allows us to manage the rollout of a resource kubectl rollout status -w -f deploy/go-demo-2-api.yml

kubectl rollout history -f deploy/go-demo-2-api.yml

  • This lets us see how many revisions of the software there have been, and which command created each revision. kubectl rollout undo -f deploy/go-demo-2-api.yml kubectl rollout undo -f deploy/go-demo-2-api.yml --to-revision=2

Set

  • set configuration properties for resources
    • ex. update docker image of a pod template, update env variables of a pod template etc.
  • note: the output of this command only indicates that the definition (ex. of the image used in the Deployment) was successfully updated. This means that if we used an image that doesn't exist, we would still get a "success" output from this command.
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