Dockerfile env dependent starting point - node.js

Question

Picking up docker, a little late to the show, but better late than never.
Following a few online tutorials i landed at a docker file and docker-compose for my 1st microservice node+mongo.
Terrible setup for dev so now will implement trusty pm2: https://dev.to/itmayziii/step-by-step-guide-to-setup-node-with-docker-2mc9
Production would want the below, but dev i would want pm2 instance mgr to reboot on file change..
But the obvious question i now have is how to differentiate between dev and prod in the Dockerfile?
Dockerfile
FROM node:12-alpine
RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app
COPY package.json /usr/src/app/
RUN npm i
COPY . /usr/src/app
EXPOSE 3000
CMD node ./build/server.js
docker-compose
version: "3"
services:
ms-authentication-service:
image: "ms-authentication-image"
depends_on:
- mongodb
build:
dockerfile: Dockerfile
context: .
links:
- mongodb
networks:
- default
ports:
- "8080:8000"
restart: always
mongodb:
image: mongo:4.2
container_name: "ms-authentication-mongo-image"
environment:
MONGO_INITDB_ROOT_USERNAME: bob
MONGO_INITDB_ROOT_PASSWORD: bob
networks:
- default
ports:
- 27017:27017

Answer 1

In general, managing environment like the staging or production based on ENV is common practice, but in the case of Docker the best approach is tag.
It's better to use tag for dev, stage and production in case of Docker. There are many reasons, one reason is mount code in development environment is fine but it is not recommended in the production environment.
When building images, always tag them with useful tags which codify
version information, intended destination (prod or test, for
instance), stability, or other information that is useful when
deploying the application in different environments. Do not rely on
the automatically-created latest tag.
Docker App development best-practices
But if still want to go with ENV approach then you can use the docker-entrypoint script.
Dockerfile
FROM node:alpine
RUN npm install pm2 -g
COPY . /app
WORKDIR /app
ENV NODE_ENV=development
RUN chmod +x docker-entrypoint.sh
ENTRYPOINT ["sh","docker-entrypoint.sh"]
Docker-entrypoint
#!bin/sh
if [ $NODE_ENV = development ]; then
pm2 start server.js
else
node server.js
fi
So you are good to go and you will able to change this in Dockerfile or run time
docker run --env NODE_ENV=production -it --rm node:production
or
docker run --env NODE_ENV=development -it --rm dev