Environment variables in Compose in Docker - Mini Project: Build & Apply

Environment variables in Compose

📖 Scenario: You are setting up a simple web application using Docker Compose. You want to use environment variables to configure the application port and a greeting message.

🎯 Goal: Build a Docker Compose file that uses environment variables to set the port and greeting message for a web service.

📋 What You'll Learn

Create a Docker Compose file with a service named webapp

Use environment variables APP_PORT and GREETING in the Compose file

Set default values for these environment variables in the Compose file

Print the environment variables inside the container using a simple command

💡 Why This Matters

🌍 Real World

Environment variables in Docker Compose help configure containers without changing code or images. This is common in real projects to manage settings like ports, credentials, or messages.

💼 Career

Understanding environment variables in Compose is essential for DevOps roles to build flexible, configurable containerized applications.

1

Create the basic Docker Compose file

Create a file named docker-compose.yml with a service called webapp that uses the image alpine and runs the command sh -c "echo Hello".

Docker

# Create docker-compose.yml with service webapp using alpine image and command to echo Hello
# Your code here

Need a hint?

Use the services key, then define webapp with image and command.

2

Add environment variables with default values

Add environment variables APP_PORT with default 8080 and GREETING with default Hello, World! under the webapp service using the environment key.

Docker

version: '3.8'
services:
  webapp:
    image: alpine
    command: sh -c "echo Hello"
    # Add environment variables APP_PORT=8080 and GREETING='Hello, World!'
    # Your code here

Need a hint?

Use the environment key as a map with keys APP_PORT and GREETING.

3

Modify the command to print environment variables

Change the command of the webapp service to print both environment variables APP_PORT and GREETING using sh -c and echo. The command should print: Port: $APP_PORT, Message: $GREETING.

Docker

version: '3.8'
services:
  webapp:
    image: alpine
    # Change command to print environment variables APP_PORT and GREETING
    # Your code here
    environment:
      APP_PORT: 8080
      GREETING: "Hello, World!"

Need a hint?

Use sh -c "echo Port: $APP_PORT, Message: $GREETING" as the command.

4

Run the Compose service and show output

Run docker-compose run webapp and print the output that shows the port and greeting message from the environment variables.

Docker

# Run the command 'docker-compose run webapp' in your terminal to see the output
# Your code here

Need a hint?

Use the terminal command docker-compose run webapp to see the output.