I have an environment file that contain a variable called Database_User.
In my docker-compose, I have this:
services:
database:
container_name: postgres
hostname: db
image: postgres:12-alpine
environment:
- POSTGRES_USER=${Database_User}
ports:
- "54321:5432"
env_file: project/myproject/.env
But, I am getting an error:
The Database_User variable is not set. Defaulting to a blank string.
To get this right it is important to correctly understand the differences between the environment and env_file properties and the .env file:
environment and env_file let you specify environment variables to be set in the container:
environment you can specify the variables explicitly in the docker-compose.ymlenv_file you implicitly import all variables from that file.env file is loaded by docker-compose into the environment of docker-compose itself where it can be used
docker-compose with respective CLI environment variablesdocker-compose.ymlSo your current configuration does not do what you probably think it does:
env_file: project/myproject/.env
Will load that .env file into the environment of the container and not of docker-compose. Therefor Database_User won't be set for variable substitution:
environment:
- POSTGRES_USER=${Database_User}
The solution here: remove env_file from your docker-compose.yml and place .env in the same directory you are starting docker-compose from. Alternatively you can specify an .env file by path with the --env-file flag:
docker-compose --env-file project/myproject/.env up
docker-compose loading variables automatically , so how I can use in environment: ?
docker-compose documentation, it explains all this with small examples.
COMPOSE_ENV_FILES also can be used, e.g. COMPOSE_ENV_FILES=.env,.env.dev docker compose ... but not inside the actual .env file.EDIT: This answer clearly explains the important difference from defining environment variables in an env file vs using variable substitution in a docker-compose file. I have edited my answer for clarity but please make sure you also understand the other answer.
You likely have not set the environment variable Database_User for variable substitution to work and need to source wherever you have that defined before running docker-compose.
source ./database_user_defined_here.env
docker-compose up
You can review the docs on environment variable substitution: https://docs.docker.com/compose/environment-variables/#substitute-environment-variables-in-compose-files
If you're using an environment file, you shouldn't have to specify the environment section (then just define POSTGRES_USER=... in that file). Then you'd run:
docker-compose --env-file ./your-env-file.env up
Or you can also specify the env file in docker-compose.yml:
database:
...
env_file:
- your-env-file.env
However, you must specify the environment variables explicitly in this file. These docs go over env file syntax.
env_file configuration option and the --env_file flag since they're doing very different things! see my answer
.env fileDatabase_User? If you have defined Database_User in your .env file, can run source your.env to set these variables before running docker-compose up as stated in option 1. However, make sure you do not use the env_file property in this case since as stated by @acran, mixing these can easily to unexpected behavior.