Using environment variables

Goal:

Extract the environment variables into a separate file, to keep the docker-compose.yml file free of sensitive information.

Step 1: Create a .env file

Create a new file named .env in the same directory as your docker-compose.yml file. This file will contain all the environment variables for your services.

MYSQL_ROOT_PASSWORD=root
MYSQL_DATABASE=mydb
MYSQL_USER=user
MYSQL_PASSWORD=secret
SPRING_DATASOURCE_URL=jdbc:mysql://db:3306/mydb
SPRING_DATASOURCE_USERNAME=user
SPRING_DATASOURCE_PASSWORD=secret
SPRING_JPA_HIBERNATE_DDL_AUTO=update

Make sure to add the .env file to your .gitignore file to prevent it from being committed to version control, as it contains sensitive information.

Step 2: Using environment variables in docker-compose.yml

Now that we have our environment variables defined in the .env file, we can reference them in our docker-compose.yml file.

services:
  db:
    image: mysql:8.0
    environment:
      MYSQL_ROOT_PASSWORD: ${MYSQL_ROOT_PASSWORD}
      MYSQL_DATABASE: ${MYSQL_DATABASE}
      MYSQL_USER: ${MYSQL_USER}
      MYSQL_PASSWORD: ${MYSQL_PASSWORD}
    ports:
      - "3307:3306"
    volumes:
      - db_data:/var/lib/mysql
    healthcheck:
      test: ["CMD", "mysqladmin", "ping", "-h", "localhost"]
      interval: 20s
      retries: 5

  app:
    build:
      context: .
      dockerfile: Dockerfile
    environment:
      SPRING_DATASOURCE_URL: ${SPRING_DATASOURCE_URL}
      SPRING_DATASOURCE_USERNAME: ${SPRING_DATASOURCE_USERNAME}
      SPRING_DATASOURCE_PASSWORD: ${SPRING_DATASOURCE_PASSWORD}
      SPRING_JPA_HIBERNATE_DDL_AUTO: ${SPRING_JPA_HIBERNATE_DDL_AUTO}
    ports:
      - "8080:8080"
    depends_on:
      db:
        condition: service_healthy

volumes:
  db_data:

Step 3: Starting the services

Start the services using the following command:

docker compose up -d

This will create and start the containers in detached mode. You can check the status of the containers using the following command:

docker ps -a

Step 4: Checking environment variables inside a container

To check that the environment variables are correctly set inside the running container, you can use the following command to enter the container:

docker exec -it <app_container_id> sh

Once inside the container, you can use the printenv command to display all environment variables:

printenv

Verify that the environment variables are the same as those defined in the .env file.

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Notice that we could also pass the printenv command directly to docker exec without entering the container:

docker exec <app_container_id> printenv

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Step 5: Tear down

Stop and remove the containers and volumes using the following command:

docker compose down -v