Docker Compose: Change env variables

Question

I have writte a docker-compose.yml file to create a multi-container app with nodejs and mongodb (so 2 containers), and I want to make some options configurable, as the choice of server address and port. To do that, I have written what follows in docker-compose.yml to set them as env variables:

..
    web:
      environment:
        - PORT=3000
        - ADDRESS=xxx.xxx.xxx.xxx
..

Within the source code of my application, I use process.env.PORT and process.env.ADDRESS to refer to these variables.

But how can I do if I want to change those values, and for example set PORT=3001? I have to use docker-compose build and docker-compose up again and build all the application, included mongodb container?

Answer 1

I have to use docker-compose build and docker-compose up again and build all the application, included mongodb container?

Not build, just up. They are runtime options, not build options. Changing them in the docker-compose.yml file and then doing a docker-compose up again should recreate the containers with the new environment variables.

Alternatively, you can specify environment variables outside the docker-compose.yml file to make for easier changes:

1. One of these methods is to use a .env file in the same folder that you execute docker-compose form (see https://docs.docker.com/compose/env-file/ for information on it).
2. Another option is to interpolate environment variables from your shell. You could specify them such as - PORT=${APP_PORT} and then export APP_PORT=3000 on your shell before running docker-compose. See https://docs.docker.com/compose/environment-variables/ for more information.