docker-compose override application properties - variables

Question

Having a Spring Boot application we are using application.yml file to store properties. I got a task to give a user a possibility to override some properties while starting an application. Taking into consideration we have dockerised our app docker-compose file is the very right place I believe for that. I found one option which works actually, env_file:
backend:
build:
context: backend
dockerfile: Dockerfile.backend
restart: always
ports:
- 3000:3000
env_file:
- backend/custom.env
volumes:
- ../m2_repo:/root/.m2/
- ../{APP_NAME}/data_sources:/backend/data_sources/
links:
- database
networks:
main:
aliases:
- backend
This solves perfectly my task and all the KEY=VALUE pairs override existing in application.yml properties. However, I have 2 questions:
It appeared that having multiple services in my docker-compose file I need specify a separate env_file for each service, which is probably not very convenient. Is there a possibility to have one common env_file for the whole docker-compose file?
I know that for docker-compose run command there is an option -e where i can put key=value pairs of env variables. Is there any similar option for docker-compose up? I mean in order not to use env_file at all.

Answer 1

Ad 1: It is not possible. I also believe it is intentional - to make the developer define what container has access to what .env data.
Ad 2: No, you cannot supply the variables using a runtime parameter of up command of docker-compose (run docker-compose help up to see the available runtime params). But you can define these using environment clause from within a compose file, like:
restart: always
ports:
- 3000:3000
env_file:
- backend/custom.env
environment:
- DB_PASSWORD # <= #1
- APP_ENV=production # <= #2
ie.
either just a name of the env var - its value is then taken from the host machine
or the whole definition to create a new one to be available within a container
See docs on environment clause for more clarification.
Another thing you can do in order to override some settings is to extend the compose file using a "parent" one. Docs on extends clause
Unfortunately as of now, extends won't work when using compose file of version 3, but it is being discussed in this github issue, so hopefully it will be available soon:)