Docker compose environment variables - docker

Question

I'm trying to containerize a demo nodejs + reactjs + postgresql application and the directory structure looks something like this:
demo:
-client
-.env
- Dockerfile.client
- package.json
-server
- .env
- Dockerfile.server
- package.json
.env
docker-compose.yml
docker-compose.yml
version: '3.8'
services:
client:
container_name: ${APP_NAME}_fe
build:
dockerfile: ./client/Dockerfile.client
environment:
CHOKIDAR_USEPOLLING: "true"
image: ${APP_NAME}_img_fe
volumes:
- ./client:/app
- /app/node_modules
ports:
- 3000:3000
server:
container_name: ${APP_NAME}_be
build:
# context: .
dockerfile: ./server/Dockerfile.server
image: ${APP_NAME}_img_be
volumes:
- ./server:/app
- /app/node_modules
ports:
- 5000:5000
db:
container_name: ${APP_NAME}_db
image: postgres
build:
# context: .
dockerfile: ./server/Dockerfile.db
env_file: ./server/.env
environment:
POSTGRES_PASSWORD: ${DB_PASSWORD}
POSTGRES_USER: ${DB_USER}
POSTGRES_DB: ${APP_NAME}
volumes:
- db-data:/var/lib/postgresql/data
ports:
- 5432:5432
volumes:
db-data:
name: ${APP_NAME}_db
I'm trying to keep all the sensitive data(like passwords and keys), api urls or ports inside .env files so i have all the infos in just one place, something like this:
.env from server
PORT=5000
DB_PASSWORD=postgres
DB_USER=postgres
DB_NAME=demo
.env on root level
APP_NAME=demo
The problem is for the db service (postgres container) the credentials are not visible at the creation time, so i need to hardcode them like:
environment:
POSTGRES_PASSWORD: postgres
POSTGRES_USER: postgres
POSTGRES_DB: demo
Is there a way to fetch these values from inside the .env files ?
LE: I think one way is to keep only one .env at the root of the application with:
-db password
-db user
-port(both server and client)
-api url
In this case i need to acces .env from client and server folder.
Not sure this is a common practice or not.
Thank you.

Answer 1

You don't need to access the .env file from your applications. You can substitute variables in the docker-compose.yml parsing context by simply running the docker-compose up in the right folder.
The issue that you're running through is probably because you have multiple .env files distributed across your project, with different values.
From the documentation:
If you have multiple environment variables, you can substitute them by providing a path to your environment variables file. By default, the docker-compose command will look for a file named .env in the directory you run the command. By passing the file as an argument, you can store it anywhere and name it appropriately, for example, .env.ci, .env.dev, .env.prod. Passing the file path is done using the --env-file option:
That means that not only it's a good practice to keep .env files but also that you probably should keep only one .env file and run the docker-compose up command from the folder that keeps that file (usually the project root folder).

Answer 2

it seems to me that at your environment, '-' this symbol is missing. So it would be
environment:
- POSTGRES_PASSWORD: ${DB_PASSWORD}
- POSTGRES_USER: ${DB_USER}
- POSTGRES_DB: ${APP_NAME}
and keep docker-compose.yaml and .env file under the same directory and try
docker-compose up -d
I always use -d to start as background job, daemon thread.
Also you can see the list of environment variables of Postgres at this link:
https://hub.docker.com/_/postgres