ReplicaSet definition in Kubernetes - Mini Project: Build & Apply

ReplicaSet definition

📖 Scenario: You are managing a simple web application on Kubernetes. To keep your app running smoothly, you want to make sure there are always exactly 3 copies (pods) of your app running. This helps if one pod stops working, others keep serving users.

🎯 Goal: Create a Kubernetes ReplicaSet definition YAML that ensures 3 replicas of a pod running the nginx container. This ReplicaSet will keep your app available by automatically replacing pods if they fail.

📋 What You'll Learn

Create a ReplicaSet named nginx-replicaset

Set the number of replicas to 3

Use the label app: nginx for pods

Define a pod template with a container named nginx using the image nginx:latest

Expose container port 80

💡 Why This Matters

🌍 Real World

ReplicaSets are used in Kubernetes to keep a set number of pod copies running. This helps maintain application availability and reliability.

💼 Career

Understanding ReplicaSets is essential for Kubernetes administrators and DevOps engineers to manage application scaling and fault tolerance.

1

Create the basic ReplicaSet structure

Write the first lines of the ReplicaSet YAML with apiVersion: apps/v1, kind: ReplicaSet, and metadata with name: nginx-replicaset.

Kubernetes

# Your code here

Need a hint?

Start by defining the API version, kind, and metadata name exactly as shown.

2

Add the replicas count and selector

Add a spec section with replicas: 3 and a selector that matches pods with label app: nginx.

Kubernetes

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: nginx-replicaset
# Add spec with replicas and selector here

Need a hint?

Under spec, set replicas to 3 and define selector.matchLabels.app as nginx.

3

Define the pod template with container details

Inside spec, add template with metadata.labels matching app: nginx. Under template.spec.containers, define a container named nginx using image nginx:latest and expose port 80.

Kubernetes

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: nginx-replicaset
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
# Add template with pod labels and container details here

Need a hint?

Make sure pod labels match the selector labels exactly. Define container name, image, and port as specified.

4

Output the complete ReplicaSet YAML

Print the full ReplicaSet YAML to verify your definition.

Kubernetes

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: nginx-replicaset
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:latest
        ports:
        - containerPort: 80
# Print the YAML content here

Need a hint?

Check your YAML matches the full ReplicaSet definition exactly.