如何使用 dockerfile 访问环境变量

Question

I'm stuck with my dockerfile, i'll try to get acces to an env. variable who is declaring in my docker-compose.yml but it tell me that the variable do not exist.

docker-compose.yml

my-project-dev:
container_name: my-project-frontend
build:
  context: .
  dockerfile: Dockerfile
volumes:
  - './my-project-frontend:/usr/src/app'
  - '/usr/src/app/node_modules'
ports:
  - 15242:80
  # - 49153:49153
environment:
  - ENV=dev

dockerfile

FROM node:16.14.2 as builder
RUN mkdir /usr/src/app
WORKDIR /usr/src/app
ENV PATH /usr/src/app/node_modules/.bin:$PATH
COPY . /usr/src/app
RUN npm install
RUN npm run build-${ENV}  

For debuging i try in my dockerfile to "RUN env", that's the result.

But, when my container is start and i enter on it and i execute "env" i see my "ENV" variable

Anyone have a solution?

Answer 1

Environment variable in docker-compose are intended for the application . Ie runtime environment of your application.

Dockerfile does not have environment variables. Instead - it has build arguments.

Thus, you need to use build arguments io env. variables for customization of build process.

Namely:

Dockerfile

ARG ENV=prod    # default value
RUN npm run build-${ENV}

Build script

docker build --build-arg ENV=dev

or in docker-compose :

build:
    context: .
    args:
        ENV: dev