Create config file when running Docker container with Compose

Question

I have the following Dockerfile

FROM node:10.8.0-alpine as builder

# Set working directory
RUN mkdir /usr/src
RUN mkdir /usr/src/app
WORKDIR /usr/src/app

# Add /usr/src/app/node_modules/.bin to $PATH
ENV PATH /usr/src/app/node_modules/.bin:$PATH

# Get build arguments coming from .env file
ARG API_URL
ENV API_URL "$API_URL"

# Create config file from environment variables
RUN echo "API_URL = $API_URL" > ./app.cfg

# Install and cache app dependencies
COPY package.json /usr/src/app/package.json
RUN npm install
RUN npm install [email protected] -g
COPY . /usr/src/app
RUN npm run build

# Production environment
FROM nginx:1.15.2-alpine
COPY --from=builder /usr/src/app/build /usr/share/nginx/html
CMD ["nginx", "-g", "daemon off;"]

And I use the following docker-compose.yml file to build my Docker image

version: '3'
services:

  app:
    container_name: data-quality-app
    restart: always
    image: data-quality-app
    build:
      context: ./app
      dockerfile: Dockerfile
      args:
        - API_URL=${API_URL}
    env_file:
      - ./.env
    ports:
      - 80:80
    networks:
      - default

networks:
  default:
    external:
      name: data-quality-network

volumes:
  data-quality-db-volume:
    external: true

Note the file .env contains the environment variable API_URL=http://0.0.0.0:5433/graphql

All this works pretty well, but when I run my container with Docker Compose:

$ docker-compose up app

I would like to overwrite the file app.cfg in the container in order to replace the value of API_URL by its current value in the file .env.

I have tried to add the following ENTRYPOINT in Dockerfile but it did not work:

[...]
# Create config file to from environment variables
RUN echo "API_URL = $API_URL" > ./app.cfg
ENTRYPOINT echo "API_URL = $API_URL" > ./app.cfg
[...]

What am I missing?

David Maze · Accepted Answer · 2018-09-18 09:47:35Z

2

You should write an entrypoint script that does the required setup, then runs the command passed to the container.

entrypoint.sh:

#!/bin/sh
if [ -n "$API_URL" ]; then
  echo "API_URL = $API_URL" > app.cfg
fi
exec "$@"

Dockerfile (final stage):

FROM nginx:1.15.2-alpine
COPY entrypoint.sh /
COPY --from=builder /usr/src/app/build /usr/share/nginx/html
ENTRYPOINT ["/entrypoint.sh"]
CMD ["nginx", "-g", "daemon off;"]

You can debug this by running something like

docker build -t mynginx .
docker run --rm -it -e API_URL=http://test mynginx sh

which will run the entrypoint script passing it "sh" as the command; that will set up the app.cfg file and then launch the debug shell (and not nginx).

answered Sep 18, 2018 at 9:47

David Maze

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