Scaling services with replicas in Docker - Mini Project: Build & Apply

Scaling services with replicas

📖 Scenario: You are managing a simple web service using Docker. To handle more visitors, you want to run multiple copies (replicas) of your service.This project will guide you to create a Docker Compose setup and scale the service replicas.

🎯 Goal: Build a Docker Compose file to define a web service and then scale it to run multiple replicas.

📋 What You'll Learn

Create a Docker Compose file with a web service using the nginx image

Add a configuration variable for the number of replicas

Use the docker-compose command to scale the service

Display the running containers to verify scaling

💡 Why This Matters

🌍 Real World

Scaling services with replicas is common when websites or apps get more visitors. Running multiple copies helps handle more users smoothly.

💼 Career

DevOps engineers often use Docker Compose and scaling commands to manage service availability and performance in real projects.

1

Create a Docker Compose file with a web service

Create a file named docker-compose.yml with a service called web that uses the nginx:latest image.

Docker

# Create docker-compose.yml with a service named web using nginx:latest
# Your code here

Need a hint?

Use YAML syntax to define the service under services: with the name web and specify the image nginx:latest.

2

Add a variable for the number of replicas

Add a variable called REPLICAS in a .env file and set it to 3 to define how many replicas you want.

Docker

version: '3.8'
services:
  web:
    image: nginx:latest

# Create a .env file with REPLICAS=3
# Your code here

Need a hint?

Create a file named .env in the same folder as docker-compose.yml and add the line REPLICAS=3.

3

Scale the web service using the replicas variable

Use the command docker-compose up -d --scale web=${REPLICAS} to start the web service with the number of replicas from the REPLICAS variable.

Docker

version: '3.8'
services:
  web:
    image: nginx:latest

# .env file content:
REPLICAS=3

# Run the docker-compose command to scale
# Your code here

Need a hint?

Use the --scale option with docker-compose up -d and pass the replicas variable as ${REPLICAS}.

4

Display running containers to verify scaling

Run docker ps --filter name=web to list all running containers with the name web and verify that there are 3 replicas running.

Docker

version: '3.8'
services:
  web:
    image: nginx:latest

# .env file content:
REPLICAS=3

# Command to run:
docker-compose up -d --scale web=${REPLICAS}

# Run docker ps to check containers
# Your code here

Need a hint?

Use docker ps --filter name=web to see all containers with web in their name. You should see 3 containers listed.