How do make all environment variables available on the Dockerfile? - docker

Question

I have this Dockerfile
FROM node:14.17.1
ARG GITHUB_TOKEN
ARG REACT_APP_BASE_URL
ARG DATABASE_URL
ARG BASE_URL
RUN mkdir /usr/src/app
WORKDIR /usr/src/app
ENV PATH /usr/src/app/node_modules/.bin:$PATH
ENV GITHUB_TOKEN=${GITHUB_TOKEN}
ENV REACT_APP_BASE_URL=${REACT_APP_BASE_URL}
ENV DATABASE_URL=${DATABASE_URL}
ENV BASE_URL=${BASE_URL}
ENV PORT 80
COPY . /usr/src/app
RUN npm install
RUN npm run build
EXPOSE 80
CMD ["npm", "start"]
But I don't like having to set each environment variable. Is is possible to make all of them available without needing to set one by one?

Answer 1

We need to pay attention to next two items before continue:
As mentioned by #Lukman in comments, TOKEN is not a good item to be stored in image unless you totally for internal use, you decide.
Even we did not specify environment one by one in Dockerfile, we still need to define them in some other place, as program itself can't know what environment you really need.
If you no problem with above, let's go on. Basically, I think define the environment (Here, use ENV1, ENV2 as example) in a script, then source them in container, and let app have ways to access these variables is what you needed.
env.sh:
export ENV1=1
export ENV2=2
app.js:
#!/usr/bin/env node
var env1 = process.env.ENV1;
var env2 = process.env.ENV2;
console.log(env1);
console.log(env2);
entrypoint.sh:
#!/bin/bash
source /usr/src/app/env.sh
exec node /usr/src/app/app.js
Dockerfile:
FROM node:14.17.1
WORKDIR /usr/src/app
COPY . /usr/src/app
RUN chmod -R 755 /usr/src/app
CMD ["/usr/src/app/entrypoint.sh"]
Execution:
$ docker build -t abc:1 .
$ docker run --rm abc:1
1
2
Explain:
We change CMD or ENTRYPOINT in Dockerfile to use customized entrypoint.sh, in this entrypoint.sh, we will first source env.sh which make ENV1 and ENV2 visible to subprocess of entrypoint.sh.
Then, we use exec to replace current process as node app.js, so PID1 becomes node app.js now, meanwhile app.js still could get the environment defined in env.sh.
With above, we no need to define variables in Dockerfile one by one, but still our app could get the environment.

Answer 2

Here's a different (easy) way.
Start by making your file. Here I'm choosing to use everything on my this is messy and not recommended. It's a useful bit of code though so I thought I'd add it.
env | sed 's/^/export /' > env.sh
edit it so you only have what you need
vi env.sh
Use the below to import files into the container. Change pwd to whichever folder you want to share. Using this carelessly may result in you sharing to many files*
sudo docker run -it -v `pwd`:`pwd` ubuntu
Assign appropriate file permissions. I'm using 777 which means anyone can read, write, execute - for demonstration purposes. But you only need execute privileges.
Run this command and make sure you add the full stop.
. /LOCATION/env.sh
If you're confused to where your file is just type pwd in the host console.
You can just add those commands where appropriate to your Dockerfile to automate the process. If I recall there is a VOLUME flag for Dockerfile.