Kubernetes Commands

Introduction

Kubernetes is a powerful container orchestration platform that helps you deploy, scale, and manage containerized applications. One of the fundamental skills for working with Kubernetes is mastering its command-line tool, kubectl. This tool allows you to communicate with your Kubernetes cluster and perform various operations.

In this guide, we'll explore the most common and useful Kubernetes commands that will help you manage your clusters effectively. Whether you're setting up a development environment or managing production workloads, these commands will form the foundation of your Kubernetes journey.

Getting Started with kubectl

Before diving into specific commands, let's understand how to install and set up kubectl.

Installing kubectl

The kubectl command-line tool is necessary to interact with any Kubernetes cluster. Here's how to install it on different operating systems:

For macOS (using Homebrew):

bash

brew install kubectl

For Ubuntu/Debian:

bash

sudo apt-get update && sudo apt-get install -y kubectl

For Windows (using Chocolatey):

bash

choco install kubernetes-cli

Verify your installation:

bash

kubectl version --client

Output will look something like:

Client Version: version.Info{Major:"1", Minor:"25", GitVersion:"v1.25.4", GitCommit:"872a965c6c6526caa949f0c6ac028ef7aff3fb78", GitTreeState:"clean", BuildDate:"2022-11-09T13:36:36Z", GoVersion:"go1.19.3", Compiler:"gc", Platform:"darwin/amd64"}

Configuring kubectl

kubectl needs to know which cluster to communicate with and how to authenticate. This information is stored in a configuration file called kubeconfig.

The default location is ~/.kube/config, but you can specify a different location using the --kubeconfig flag or the KUBECONFIG environment variable.

To view your current configuration:

bash

kubectl config view

To set a specific context (cluster):

bash

kubectl config use-context my-cluster-name

Essential Kubernetes Commands

Cluster Information Commands

These commands help you understand your cluster's state and configuration.

Check cluster info

bash

kubectl cluster-info

Output:

Kubernetes control plane is running at https://kubernetes.docker.internal:6443
CoreDNS is running at https://kubernetes.docker.internal:6443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy

List all nodes in the cluster

bash

kubectl get nodes

Output:

NAME             STATUS   ROLES           AGE     VERSION
docker-desktop   Ready    control-plane   7d14h   v1.25.4

Get detailed information about a specific node

bash

kubectl describe node node-name

Resource Management Commands

Kubernetes organizes resources into different namespaces. Here are commands to work with them:

List all namespaces

bash

kubectl get namespaces

Output:

NAME              STATUS   AGE
default           Active   7d14h
kube-node-lease   Active   7d14h
kube-public       Active   7d14h
kube-system       Active   7d14h

Create a namespace

bash

kubectl create namespace my-namespace

Set the default namespace for kubectl commands

bash

kubectl config set-context --current --namespace=my-namespace

Pod Management Commands

Pods are the smallest deployable units in Kubernetes.

List all pods

bash

kubectl get pods

With more details:

bash

kubectl get pods -o wide

In all namespaces:

bash

kubectl get pods --all-namespaces

Describe a specific pod

bash

kubectl describe pod pod-name

Creating a pod from a YAML file

bash

kubectl apply -f pod-definition.yaml

Get pod logs

bash

kubectl logs pod-name

Follow logs in real-time:

bash

kubectl logs -f pod-name

Execute a command in a pod

bash

kubectl exec -it pod-name -- /bin/bash

Delete a pod

bash

kubectl delete pod pod-name

Deployment Commands

Deployments manage ReplicaSets, which ensure a specified number of pod replicas are running.

Create a deployment

bash

kubectl create deployment nginx-deployment --image=nginx

List all deployments

bash

kubectl get deployments

Scale a deployment

bash

kubectl scale deployment nginx-deployment --replicas=5

Update a deployment's image

bash

kubectl set image deployment/nginx-deployment nginx=nginx:1.19

View the rollout status

bash

kubectl rollout status deployment/nginx-deployment

Rollback a deployment

bash

kubectl rollout undo deployment/nginx-deployment

Delete a deployment

bash

kubectl delete deployment nginx-deployment

Service Commands

Services provide stable network endpoints for pods.

List all services

bash

kubectl get services

Create a service (exposing a deployment)

bash

kubectl expose deployment nginx-deployment --port=80 --type=LoadBalancer

Describe a service

bash

kubectl describe service service-name

Delete a service

bash

kubectl delete service service-name

Practical Examples

Let's go through some practical examples to see how these commands work together in real-world scenarios.

Example 1: Deploying a Web Application

Let's deploy a simple web application and expose it to the internet:

bash

# Create a deployment
kubectl create deployment web-app --image=nginx

# Verify the deployment
kubectl get deployments
kubectl get pods

# Expose the deployment as a service
kubectl expose deployment web-app --port=80 --type=LoadBalancer

# Check the service details
kubectl get services

Example 2: Scaling and Updating an Application

Now, let's scale our application and then update it:

bash

# Scale the deployment to 3 replicas
kubectl scale deployment web-app --replicas=3

# Verify the scaling
kubectl get pods

# Update the application image
kubectl set image deployment/web-app nginx=nginx:alpine

# Check the rollout status
kubectl rollout status deployment/web-app

# View the update history
kubectl rollout history deployment/web-app

Example 3: Debugging a Failed Pod

When pods fail, you need to troubleshoot:

bash

# Identify the failed pod
kubectl get pods

# View detailed information about the pod
kubectl describe pod failed-pod-name

# Check the logs
kubectl logs failed-pod-name

# If needed, get a shell into the container
kubectl exec -it failed-pod-name -- /bin/sh

Working with Configuration

ConfigMaps and Secrets

ConfigMaps and Secrets help you manage configuration data separately from your application code.

Create a ConfigMap

bash

kubectl create configmap app-config --from-literal=APP_ENV=production --from-literal=APP_DEBUG=false

View ConfigMaps

bash

kubectl get configmaps
kubectl describe configmap app-config

Create a Secret

bash

kubectl create secret generic app-secrets --from-literal=DB_PASSWORD=mypassword

View Secrets

bash

kubectl get secrets
kubectl describe secret app-secrets

Command Flow Visualization

Here's a visualization of the command flow for a typical Kubernetes application lifecycle:

Tips and Tricks

1. Use Aliases

Create aliases for frequently used commands:

bash

alias k='kubectl'
alias kg='kubectl get'
alias kd='kubectl describe'

2. Use kubectl Output Formats

kubectl can output data in different formats:

bash

# Output in JSON format
kubectl get pods -o json

# Output in YAML format
kubectl get pods -o yaml

# Output specific fields using jsonpath
kubectl get pods -o jsonpath='{.items[0].metadata.name}'

# Custom columns
kubectl get pods -o custom-columns=NAME:.metadata.name,STATUS:.status.phase

3. Use context switching

If you work with multiple clusters:

bash

# List all contexts
kubectl config get-contexts

# Switch context
kubectl config use-context my-other-cluster

Summary

In this guide, we've covered the essential Kubernetes commands that you'll need to manage your clusters effectively. From basic cluster information and pod management to advanced deployment strategies and configuration, these commands form the backbone of Kubernetes operations.

Remember that mastering kubectl is a journey. Start with these fundamentals and gradually explore more complex commands as you become comfortable with the basics.

Additional Resources

To continue your Kubernetes learning journey:

1. The official Kubernetes documentation
2. The kubectl cheat sheet
3. The kubectl command reference

Exercises

To practice what you've learned:

1. Deploy a simple multi-container application using a YAML manifest.
2. Scale the application up and down, and observe the changes.
3. Update the application to a newer version and then roll back to the previous version.
4. Create a ConfigMap and a Secret, and mount them into your application.
5. Troubleshoot a failing pod by examining its logs and events.

Happy Kubernetes journey!