Passing env variables from one service to another inside docker-compose.yml

Question

Is there a way to pass environment variables from one service to the other inside docker-compose.yml ?

services:
 testService:
    environment:
      TEST_KEY: 1234
 testServiceTests:
    environment:
      TEST_KEY: I want to pull in the value 1234 here from service1
    

Answer 1

No.

However, there's an alternative. You may provide environment variables to all the services within the Docker Compose file by exposing them either from your shell, when you run the Compose or by using a special .env file, See documentation .

Using this approach, you would have a global (for the Compose) environment variable, say GLOBAL_TEST_KEY (it needn't have a different name) and you would be able to share this across multiple services:

services:
 testService:
    environment:
      TEST_KEY: ${GLOBAL_TEST_KEY}
 testServiceTests:
    environment:
      TEST_KEY: ${GLOBAL_TEST_KEY}

And then: docker-compose run -e GLOBAL_TEST_KEY="Some value" ....

Or, create a file called .env alongside docker-compose.yaml and, in .env :

GLOBAL_TEST_KEY="Some value"

And then: docker-compose run ...

NOTE No need to reference .env as it's included by default