How do I use environment variables in Docker Compose?

How do I use environment variables in Docker Compose?

You can define environment variables in your docker-compose.yml file using the environment key. For example:

services:
  app:
    image: myapp
    environment:
      - MY_ENV_VAR=value

Can I use a .env file for environment variables?

Yes, you can use a .env file to define your environment variables. Docker Compose will automatically read this file. Just create a .env file with your variables:

MY_ENV_VAR=value

How do I reference these variables in my docker-compose.yml?

You can reference the variables in your docker-compose.yml using the syntax ${VARIABLE_NAME}. For example:

services:
  app:
    image: myapp
    environment:
      - MY_ENV_VAR=${MY_ENV_VAR}

What if I want to set default values for these variables?

You can set default values directly in the docker-compose.yml file using the syntax:

services:
  app:
    image: myapp
    environment:
      - MY_ENV_VAR=${MY_ENV_VAR:-default_value}