Docker Compose will auto load .env variable

 Docker Compose retrieves environment variables from a .env file located in the same directory as your docker-compose.yml file. This is the default and most common method.

How it works:

Placement:

Create a file named .env in the root directory of your Docker Compose project, alongside your docker-compose.yml file.

Content:

Define your environment variables within this .env file using a simple key-value pair format, one variable per line:

Code

    VARIABLE_NAME=variable_value

    ANOTHER_VAR=another_value

Referencing in docker-compose.yml: In your docker-compose.yml file, you can then reference these variables using the ${VARIABLE_NAME} syntax for interpolation:

Code

    version: '3.8'

    services:

      web:

        image: "my-app:${APP_VERSION}"

        environment:

          - DB_HOST=${DATABASE_HOST}

Automatic Loading: When you run docker compose up (or docker-compose up with older versions), Docker Compose automatically detects and loads the variables from the .env file, substituting them into your docker-compose.yml configuration before creating and starting the services.