Using docker env vars to set config file in image at run time

docker-compose.yml

# this file is intended to be used in the local build environment
# to get started, run:
#
#   docker-compose up
#


# REQUIRES docker-compose 1.16+
version: '2.3'


services:
  signup:
    build:
      context: .
      target: build
    ports:
      - '9000:9000'
    environment:
      - FUN_VAR_HERE

entrypoint.sh

#!/bin/sh

set -xe

echo "window.CONFIG=`jq -n env`" > /dist/config.js
exec "$@"

gistfile1.txt

##############
## BUILD IMAGE
##############
FROM node:8 AS build
LABEL builder=true

RUN apt-get update \
  && apt-get install -y gnupg nginx curl \
  && curl https://github.com/stedolan/jq/releases/download/jq-1.5/jq-linux64 -Lo /usr/bin/jq \
  && chmod +x /usr/bin/jq \
  && rm -rf /var/lib/apt/lists

COPY nginx.conf /etc/nginx/conf.d/default.conf
COPY . /client

WORKDIR /client

RUN yarn && npm run build

EXPOSE 9000

ENTRYPOINT ["/client/entrypoint.sh"]
CMD ["sh", "-c", "(npm run dev &) && nginx -g 'daemon off;'"]





##############
## DIST IMAGE
##############
FROM alpine AS dist

COPY --from=build /dist /dist

COPY nginx.conf /etc/nginx/conf.d/default.conf
COPY entrypoint.sh /entrypoint.sh

RUN apk update \
  && apk add jq nginx \
  && mkdir -p /run/nginx \
  && ln -sf /dev/stdout /var/log/nginx/access.log \
  && ln -sf /dev/stderr /var/log/nginx/error.log \
  && rm -rf /var/lib/apt/lists

EXPOSE 9000

ENTRYPOINT ["/entrypoint.sh"]
CMD ["nginx", "-g", "daemon off;"]