How to use environment variables in docker compose

Question

I would like to be able to use env variables inside docker-compose.yml, with values passed in at the time of docker-compose up. This is the example.

I am

Answer 1

The best way is to specify environment variables outside the docker-compose.yml file. You can use env_file setting, and define your environment file within the same line. Then doing a docker-compose up again should recreate the containers with the new environment variables.

Here is how my docker-compose.yml looks like:

services:
  web:
    env_file: variables.env

Note: docker-compose expects each line in an env file to be in VAR=VAL format. Avoid using export inside the .env file. Also, the .env file should be placed in the folder where the docker-compose command is executed.