Environment files (.env) in Docker - Mini Project: Build & Apply

Using Environment Files (.env) with Docker

📖 Scenario: You are creating a simple Docker container that needs to use environment variables for configuration. Instead of hardcoding these variables inside the Dockerfile or docker run command, you will use an environment file (.env) to keep your settings organized and easy to change.This is like writing down your secret recipe on a note instead of memorizing it every time you cook. It helps keep things clean and safe.

🎯 Goal: Build a Docker setup that reads environment variables from a .env file and uses them inside a container.You will create the .env file, configure Docker to use it, and then run a container that prints the environment variables.

📋 What You'll Learn

Create a .env file with specific environment variables

Write a simple Dockerfile that uses an environment variable

Configure Docker Compose to load the .env file

Run the container and display the environment variables

💡 Why This Matters

🌍 Real World

Environment files are used in real projects to keep configuration separate from code. This makes it easy to change settings without rebuilding images or changing code.

💼 Career

Knowing how to use <code>.env</code> files with Docker is a key skill for DevOps engineers and developers working with containerized applications.

1

Create the .env file with environment variables

Create a file named .env with these exact lines:
APP_NAME=MyApp
APP_PORT=8080

Docker

# Create a .env file with APP_NAME=MyApp and APP_PORT=8080
# Your code here

Need a hint?

Use a text editor to create a file named .env and add the two lines exactly as shown.

2

Write a simple Dockerfile that uses the environment variables

Create a Dockerfile with these exact lines:
FROM alpine
ENV APP_NAME=$APP_NAME
ENV APP_PORT=$APP_PORT
CMD ["sh", "-c", "echo Running $APP_NAME on port $APP_PORT"]

Docker

APP_NAME=MyApp
APP_PORT=8080

# Create a Dockerfile with FROM alpine and ENV variables
# Your code here

Need a hint?

Write a Dockerfile starting with FROM alpine. Use ENV to set APP_NAME and APP_PORT from the environment variables. Use CMD to print a message using these variables.

3

Create a docker-compose.yml file to load the .env file

Create a docker-compose.yml file with these exact contents:

version: '3.8'
services:
  app:
    build: .
    env_file:
      - .env

Docker

APP_NAME=MyApp
APP_PORT=8080

FROM alpine
ENV APP_NAME=$APP_NAME
ENV APP_PORT=$APP_PORT
CMD ["sh", "-c", "echo Running $APP_NAME on port $APP_PORT"]

# Create docker-compose.yml with version 3.8, service app, build ., and env_file .env
# Your code here

Need a hint?

Create a docker-compose.yml file that builds the current directory and loads the .env file using env_file.

4

Run the container and display the environment variables

Run docker-compose up --build in the terminal and observe the output. The container should print:
Running MyApp on port 8080

Docker

APP_NAME=MyApp
APP_PORT=8080

FROM alpine
ENV APP_NAME=$APP_NAME
ENV APP_PORT=$APP_PORT
CMD ["sh", "-c", "echo Running $APP_NAME on port $APP_PORT"]

version: '3.8'
services:
  app:
    build: .
    env_file:
      - .env

# Run docker-compose up --build and check output
# Your code here

Need a hint?

Use the command docker-compose up --build to build and run the container. The output should show the message with the environment variables.