Getting Started With Kubectl

Note: If you are already familiar with Kubectl, you can skip this section.

This section provides a brief overview of the most basic Kubectl commands, which are described in more detail in later chapters.

For more background on the Kubernetes APIs themselves, see the docs at k8s.io.

Listing Kubernetes Resources

List the Kubernetes Deployment Resources that are in the kube-system namespace.

Note: Deployments are Resources which manage Pod replicas (Pods run Containers)

kubectl get deployments --namespace kube-system

NAME                     DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
event-exporter-v0.2.3    1         1         1            1           14d
fluentd-gcp-scaler       1         1         1            1           14d
heapster-v1.6.0-beta.1   1         1         1            1           14d
kube-dns                 2         2         2            2           14d
kube-dns-autoscaler      1         1         1            1           14d
l7-default-backend       1         1         1            1           14d
metrics-server-v0.3.1    1         1         1            1           14d

Print detailed information about the kube-dns Deployment in the kube-system namespace.

kubectl describe deployment kube-dns --namespace kube-system

Name:                   kube-dns
Namespace:              kube-system
CreationTimestamp:      Wed, 06 Mar 2019 17:36:05 -0800
Labels:                 addonmanager.kubernetes.io/mode=Reconcile
                        k8s-app=kube-dns
                        kubernetes.io/cluster-service=true
Annotations:            deployment.kubernetes.io/revision: 2
...

Creating a Resource from Config

Create or Update Kubernetes Resources from Remote Config.

kubectl apply -f https://raw.githubusercontent.com/kubernetes/kubectl/master/docs/book/examples/nginx/nginx.yaml

service/nginx created
deployment.apps/nginx-deployment created

Create or Update Kubernetes Resources from Local Config.

kubectl apply -f ./examples/nginx/nginx.yaml

service/nginx created
deployment.apps/nginx-deployment created

Print the Resources that were Applied.

kubectl get -f ./examples/nginx/nginx.yaml --show-labels

NAME            TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)   AGE   LABELS
service/nginx   ClusterIP   10.59.245.201   <none>        80/TCP    11m   <none>

NAME                               DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE   LABELS
deployment.apps/nginx-deployment   3         3         3            3           11m   app=nginx

Generating a Config from a Command

Generate Config for a Deployment Resource. This could be Applied to a cluster by writing the output to a file, and then running kubectl apply -f <yaml-file>

Note: The generated Config has extra boilerplate that users shouldn't include but exists due to the serialization process of go objects.

kubectl create deployment nginx --dry-run=client -o yaml --image nginx

apiVersion: apps/v1
kind: Deployment
metadata:
  creationTimestamp: null # delete this
  labels:
    app: nginx
  name: nginx
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  strategy: {} # delete this
  template:
    metadata:
      creationTimestamp: null # delete this
      labels:
        app: nginx
    spec:
      containers:
      - image: nginx
        name: nginx
        resources: {} # delete this
status: {} # delete this

Viewing Pods Associated with Resources

View the Pods created by the Deployment using the Pod labels.

kubectl get pods -l app=nginx

NAME                                READY   STATUS    RESTARTS   AGE
nginx-deployment-5c689d88bb-b2xfk   1/1     Running   0          10m
nginx-deployment-5c689d88bb-rx569   1/1     Running   0          10m
nginx-deployment-5c689d88bb-s7xcv   1/1     Running   0          10m

Debugging Containers

Get the logs from all Pods managed by the Deployment.

kubectl logs -l app=nginx

Get a shell into a specific Pod's Container

kubectl exec -i -t  nginx-deployment-5c689d88bb-s7xcv bash

root@nginx-deployment-5c689d88bb-s7xcv:/#

Extending kubectl

There is a plugin mechanism to adapt kubectl to your particular needs.

Show which plugins are currently available

kubectl plugin list

The easiest way to discover and install plugins is via the kubernetes sub-project krew.sigs.k8s.io.

Getting Started with Kubectl