Docker-compose volume mount before run

Question

I have a Dockerfile I'm pointing at from a docker-compose.yml.

I'd like the volume mount in the docker-compose.yml to happen before the RUN in the Dockerfile.

Dockerfile:

FROM node

WORKDIR /usr/src/app

RUN npm install --global gulp-cli 
 && npm install

ENTRYPOINT gulp watch

docker-compose.yml

version: '2'

services:
  build_tools:
    build: docker/gulp
    volumes_from:
      - build_data:rw

  build_data:
    image: debian:jessie
    volumes:
      - .:/usr/src/app

It makes complete sense for it to do the Dockerfile first, then mount from docker-compose, however is there a way to get around it.

I want to keep the Dockerfile generic, while passing more specific bits in from compose. Perhaps that's not the best practice?

question from:https://stackoverflow.com/questions/37089162/docker-compose-volume-mount-before-run

Answer 1

Erik Dannenberg's is correct, the volume layering means that what I was trying to do makes no sense. (There is another really good explaination on the Docker website if you want to read more). If I want to have Docker do the npm install then I could do it like this:

FROM node

ADD . /usr/src/app
WORKDIR /usr/src/app

RUN npm install --global gulp-cli 
 && npm install

CMD ["gulp", "watch"]

However, this isn't appropriate as a solution for my situation. The goal is to use NPM to install project dependencies, then run gulp to build my project. This means I need read and write access to the project folder and it needs to persist after the container is gone.

---

I need to do two things after the volume is mounted, so I came up with the following solution...

docker/gulp/Dockerfile:

FROM node

RUN npm install --global gulp-cli

ADD start-gulp.sh .

CMD ./start-gulp.sh

docker/gulp/start-gulp.sh:

#!/usr/bin/env bash

until cd /usr/src/app && npm install
do
    echo "Retrying npm install"
done
gulp watch

docker-compose.yml:

version: '2'

services:
  build_tools:
    build: docker/gulp
    volumes_from:
      - build_data:rw

  build_data:
    image: debian:jessie
    volumes:
      - .:/usr/src/app

So now the container starts a bash script that will continuously loop until it can get into the directory and run npm install. This is still quite brittle, but it works. :)