Deployment as higher-level abstraction in Kubernetes - Mini Project: Build & Apply

Deployment as higher-level abstraction in Kubernetes

📖 Scenario: You are managing a simple web application that needs to run reliably on Kubernetes. Instead of creating Pods directly, you will use a Deployment to manage the Pods. This helps Kubernetes keep your app running smoothly even if some Pods fail.

🎯 Goal: Create a Kubernetes Deployment YAML file that runs an NGINX web server with 3 replicas. Then, update the Deployment to change the number of replicas. Finally, display the Deployment status using kubectl commands.

📋 What You'll Learn

Create a Deployment YAML file named nginx-deployment.yaml with 3 replicas

Use the nginx:1.21 image for the container

Add a label app: nginx to the Deployment and Pod template

Update the Deployment to scale replicas from 3 to 5

Use kubectl commands to apply the Deployment and check its status

💡 Why This Matters

🌍 Real World

Deployments are used in real Kubernetes clusters to manage application Pods. They ensure your app stays running and can be updated without downtime.

💼 Career

Understanding Deployments is essential for DevOps engineers and site reliability engineers who manage containerized applications in production.

1

Create the initial Deployment YAML

Create a file named nginx-deployment.yaml with a Deployment that has replicas: 3, uses the container image nginx:1.21, and has the label app: nginx in both metadata and pod template.

Kubernetes

# Write the Deployment YAML with 3 replicas, nginx:1.21 image, and label app: nginx

Need a hint?

Remember to set replicas: 3 under spec and add app: nginx labels in both metadata and template.metadata.

2

Add a variable for replicas count

Add a comment at the top of nginx-deployment.yaml defining a variable replicaCount set to 3 to represent the number of replicas.

Kubernetes

## replicaCount: 3
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.21
        ports:
        - containerPort: 80
# Add a comment defining replicaCount variable above

Need a hint?

Add a YAML comment at the very top like ## replicaCount: 3 to represent the replicas count.

3

Update replicas count in Deployment

Change the replicas field in nginx-deployment.yaml from 3 to 5 to scale the Deployment.

Kubernetes

## replicaCount: 3
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 5
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.21
        ports:
        - containerPort: 80
# Change replicas from 3 to 5

Need a hint?

Find the replicas field under spec and change its value to 5.

4

Apply Deployment and check status

Run the command kubectl apply -f nginx-deployment.yaml to create or update the Deployment. Then run kubectl get deployment nginx-deployment to display the Deployment status.

Kubernetes

# Run kubectl commands below

Need a hint?

Use kubectl apply -f nginx-deployment.yaml to apply the Deployment and kubectl get deployment nginx-deployment to see the status. The output should show 5 replicas ready.