Kubernetes Basics - Essential Commands

K9s Dashboard Example

Download the YAML configuration file for the deployment example

Download hello-deployment.yaml

Install K9s

Windows (with Chocolatey):

choco install k9s

macOS (with Brew):

brew install k9s

Linux:

See the K9s installation guide for Linux instructions.

Create Deployment

kubectl create -f hello-deployment.yaml

Creates the deployment from the YAML file and starts the pods.

Launch K9s Dashboard

k9s

Launches the K9s dashboard in a new terminal. Watch what's happening in K9s as the pods are created.

Delete a Pod

Select a pod and press Ctrl-k in K9s

In K9s, select one of the pods and delete it by typing Ctrl-k. You'll notice that the pod will be replaced almost immediately due to the deployment's self-healing capability.

Cleanup

kubectl delete -f hello-deployment.yaml

Deletes all resources defined in the YAML configuration file.

About K9s

K9s is a terminal-based UI to interact with your Kubernetes clusters. It aims to simplify navigating, observing, and managing your applications in K8s.

Website: https://k9scli.io/

YAML Configuration File

apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello-dep
  namespace: default
spec:
  replicas: 3
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 1
  selector:
    matchLabels:
      app: hello-dep
  template:
    metadata:
      labels:
        app: hello-dep
    spec:
      containers:
      - image: gcr.io/google-samples/hello-app:1.0
        imagePullPolicy: Always
        name: hello-dep
        ports:
        - containerPort: 8080

YAML Configuration Explanation:

Deployment Structure:

apiVersion: apps/v1 → Specifies the Kubernetes API version for Deployment resources
kind: Deployment → Defines this as a Deployment resource
metadata.name: hello-dep → Names the deployment "hello-dep"
namespace: default → Places the deployment in the default namespace

Deployment Spec:

replicas: 3 → Maintains 3 identical pod instances running
strategy.type: RollingUpdate → Uses rolling update strategy for deployments
rollingUpdate.maxSurge: 1 → Allows 1 extra pod during updates
rollingUpdate.maxUnavailable: 1 → Allows 1 pod to be unavailable during updates
selector.matchLabels.app: hello-dep → Selects pods with label "app: hello-dep"

Pod Template:

template.metadata.labels.app: hello-dep → Labels the pods with "app: hello-dep"
containers → Defines the container specifications
image: gcr.io/google-samples/hello-app:1.0 → Uses the hello-app sample image
imagePullPolicy: Always → Always pulls the image when starting a pod
name: hello-dep → Names the container "hello-dep"
containerPort: 8080 → Exposes port 8080 on the container

How It Works:

This deployment creates and maintains 3 replicas of a pod running the hello-app container. The RollingUpdate strategy ensures zero-downtime deployments by gradually replacing old pods with new ones. When you delete a pod using K9s, the deployment controller immediately detects the missing pod and creates a new one to maintain the desired state of 3 replicas.