Docker port forwarding for nodejs app - node.js

Question

I'm having problems configuring docker for my nodejs app.
I have previously set up containers for both php and rails with port forwarding working flawlessly, but for this instance i can't seem to get it to work.
Running: docker ps, i get the following:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
a60f9c82d600 29c7d94a8c58 "/bin/sh -c 'npm s..." 5 seconds ago Up 3 seconds 3000/tcp romantic_albattani
As you can see I'm not getting the usual: 0.0.0.0:3000->3000/tcp that I am expecting.
docker-compose ps gives:
Name Command State Ports
------------------------------
My docker-compose.yml:
web:
build: .
volumes:
- .:/app
volumes_from:
- box
ports:
- "3000:3000"
box:
image: busybox
volumes:
- /node_modules
My Docker file:
FROM node:8.7.0
# The base node image sets a very verbose log level.
ENV NPM_CONFIG_LOGLEVEL warn
WORKDIR /tmp
COPY package.json /tmp/
RUN npm install
WORKDIR /app
ADD . /app
RUN cp -a /tmp/node_modules /app/
#ENV PORT=3000
EXPOSE 3000
CMD npm start
I'm running the command: docker-compose up --build
Any help at this point is appreciated.
I don't know if a docker inspect would be useful, but if so, tell me and i will also post it.
Edit: Changed my Dockerfile to follow the answer.

Answer 1

Your docker-compose.yml file has bad formatting, since you are not getting any errors i will assume you pasted it here wrong, here is the version with the fixed indenting:
web:
build: .
volumes:
- .:/app
volumes_from:
- box
ports:
- "3000:3000"
box:
image: busybox
volumes:
- /node_modules
Your Dockerfile has a bug, you are missing the ENTRYPOINT and/or CMD stanzas, instead you are using the RUN stanza with the wrong intent, here is a working Dockerfile with the fix applied:
FROM node:8.7.0
# The base node image sets a very verbose log level.
ENV NPM_CONFIG_LOGLEVEL warn
WORKDIR /tmp
COPY package.json /tmp/
RUN npm install
WORKDIR /app
ADD . /app
RUN cp -a /tmp/node_modules /app/
#ENV PORT=3000
EXPOSE 3000
CMD npm start
Your Dockerfile halted the execution of docker-compose at the docker image building stage because of the RUN npm start which is a process that starts and listens until stopped (because you want it to start your node app and listen for connections) causing docker-compose to never finish the docker image creating step, let alone the other steps like creating the needed containers and finish the entire docker-compose runtime process.
In short:
When you use RUN it is meant to run a command do some work and return sometime to continue the building process, it should return and exit code of 0 and the process will move on to the next Dockerfile stanza, or return another exit code and the building process will fail with an error.
When you use CMD you tell the docker image what is the starting command of all the containers started from this image (it can also be overridden at run time with docker run). It is tightly related to the ENTRYPOINT stanza, but for basic usage you are safe with the default.
Further reading: ENTRYPOINT, CMD and RUN