The objective of this post series helps you for taking the Certified Kubernetes Administrator (CKA) exam using Kubernetes Official Documentation. You don't need to install  Kubernetes  Cluster for the test that we performed on these posts. You can practice a lot with kubectl API using Katacoda.

Overview Of kubectl Command

Kubectl is a command-line interface for running commands against Kubernetes clusters. You can manage your apps and cluster and cluster resources by kubectl command. If you have already installed Kubernetes Cluster and you want to use kubectl command to manage it then check this link to install and configure kubectl command. But at this post, I will basically describe how to use it over Katacoda.

Kubectl commands use Kubeconfigfile to store Kubernetes cluster information. Basically this config file stores every information that you need to connect and run commands against the Kubernetes cluster. I want to add some information about the Kubeconfig file that helps you to understand how it works. 

Kubeconfig YAML file has three objects that Clusters, Contexts, Users.

• Clusters: This is the object that you will define your cluster information like production, test, disaster, etc. 
• Users: User information that will be used to manage the resources.
• Contexts: A context is a group of access parameters. Each context contains a Kubernetes cluster, a user, and a namespace. It's important that namespaces parameters must be defined in contexts.

Basic kubeconfigfile example;

apiVersion: v1
kind: Config

clusters:
- name: Production
  cluster:
    certificate-authority: /etc/kubernetes/pki/ca.crt
    server: https://172.17.0.35:6443

contexts:
- name: admin@Production
  context:
    cluster: Production
    user: admin
    namespace: Billing

users:
- name: admin
  user:
    client-certificate: /etc/kubernetes/pki/users/test-user/test-user.crt
    client-key: /etc/kubernetes/pki/users/test-user/test-user.key
current-context: admin@Production

You can get this information from config file located under ".kube" directory and also with kubectl command.

#cat ~/.kube/config

OR:

#kubectl config view
apiVersion: v1
clusters:
- cluster:
    certificate-authority-data: REDACTED
    server: https://172.17.0.35:6443
  name: kubernetes
contexts:
- context:
    cluster: kubernetes
    user: kubernetes-admin
  name: kubernetes-admin@kubernetes
current-context: kubernetes-admin@kubernetes
kind: Config
preferences: {}
users:
- name: kubernetes-admin
  user:
    client-certificate-data: REDACTED
    client-key-data: REDACTED

Time to test your skills. Use  Katacoda and find out the answers.

#kubectl config current-context
kubernetes-admin@kubernetes
# kubectl config view
apiVersion: v1
clusters:
- cluster:
    certificate-authority-data: REDACTED
    server: https://172.17.0.35:6443
  name: kubernetes
contexts:
- context:
    cluster: kubernetes
    user: kubernetes-admin
  name: kubernetes-admin@kubernetes
current-context: kubernetes-admin@kubernetes
kind: Config
preferences: {}
users:
- name: kubernetes-admin
  user:
    client-certificate-data: REDACTED
    client-key-data: REDACTED

#kubectl config get-contexts
CURRENT   NAME                          CLUSTER      AUTHINFO           NAMESPACE
*         kubernetes-admin@kubernetes   kubernetes   kubernetes-admin

#kubectl  config  use-context kubernetes-admin@kubernetes
Switched to context "kubernetes-admin@kubernetes".

#kubectl  cluster-info
Kubernetes master is running at https://172.17.0.11:8443
KubeDNS is running at https://172.17.0.11:8443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy

#kubectl  version 
Client Version: version.Info{Major:"1", Minor:"17", GitVersion:"v1.17.0", GitCommit:"70132b0f130acc0bed193d9ba59dd186f0e634cf", GitTreeState:"clean", BuildDate:"2019-12-07T21:20:10Z", GoVersion:"go1.13.4", Compiler:"gc", Platform:"linux/amd64"} Server Version: version.Info{Major:"1", Minor:"17", GitVersion:"v1.17.0", GitCommit:"70132b0f130acc0bed193d9ba59dd186f0e634cf", GitTreeState:"clean", BuildDate:"2019-12-07T21:12:17Z", GoVersion:"go1.13.4", Compiler:"gc", Platform:"linux/amd64"} 

-- To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'. 
#kubectl cluster-info dump

-- To further information about node and running software versions.
#kubectl get nodes -o yaml
#kubectl  get  node -o wide
NAME       STATUS   ROLES    AGE   VERSION   INTERNAL-IP   EXTERNAL-IP   OS-IMAGE             KERNEL-VERSION      CONTAINER-RUNTIME
minikube   Ready    master   23m   v1.17.0   172.17.0.11   <none>        Ubuntu 18.04.3 LTS   4.15.0-72-generic   docker://18.9.7

#kubectl get pods --all-namespaces