How to pass environment variables from docker-compose into the NodeJS project? - node.js

Question

I have a NodeJS application, which I want to docker-size.
The application consists of two parts:
server part, running an API which is taking data from a DB. This is running on the port 3000;
client part, which is doing a calls to the API end-points from the server part. This is running on the port 8080;
With this, I have a variable named "server_address" in my client part and it has the value of "localhost:3000". But here is the thing, the both projects should be docker-sized in a separate Dockerimage files and combined in one docker-compose.yml file.
So due some reasons, I have to run the docker containers via docker-compose.yml file. So is it possible to connect these things somehow and to pass the server address externally from dockerfile into the NodeJS project?
docker-composer.yml
version: "3"
services:
client-side-app:
image: my-client-side-docker-image
environment:
- BACKEND_SERVER="here we need to enter backend server"
ports:
- "8080:8080"
server-side-app:
image: my-server-side-docker-image
ports:
- "3000:3000"
both of the Dockerfile's looks like:
FROM node:8.11.1
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
CMD ["npm", "run", "dev"]
by having these files, I have the concern:
will I be able to use the variable BACKEND_SERVER somehow in the project? And if yes, how to do this? I'm not referring to the Dockerimage file, instead into the project itself?

Answer 1

Use process.env in node.js code, like this
process.env.BACKEND_SERVER
Mention your variable in docker-compose file.
version: "3"
services:
client-side-app:
image: my-client-side-docker-image
environment:
- BACKEND_SERVER="here we need to enter backend server"
ports:
- "8080:8080"
server-side-app:
image: my-server-side-docker-image
ports:
- "3000:3000"

Answer 2

In addition to the previous answer, you can alternatively define variables and their values when running a container:
docker run --env variable1=value1 --env variable2=value2 <image>
Other two different ways are: (1) referring environment variables which you’ve already exported to your local environment and (2) loading the variables from a file:
(1)
# In your ~/.bash (or ~/.zshrc) file: export VAR1=value1
docker run --env VAR1 <image>
(2)
cat env.list
# Add the following in the env.list
# variable1=value1
# variable2=value2
# variable3=value3
docker run --env-file env.list <image>
Those options are useful in case you don't want to mention your variables in the docker-compose file.
Reference