Install node_modules inside Docker container and synchronize them with host

Having run into this issue and finding the accepted answer pretty slow to copy all node_modules to the host in every container run, I managed to solve it by installing the dependencies in the container, mirror the host volume, and skip installing again if a node_modules folder is present:

Dockerfile:

FROM node:12-alpine

WORKDIR /usr/src/app

CMD [ -d "node_modules" ] && npm run start || npm ci && npm run start

docker-compose.yml:

version: '3.8'

services:
  service-1:
    build: ./
    volumes:
      - ./:/usr/src/app

When you need to reinstall the dependencies just delete node_modules.

At first, I would like to thank David Maze and trust512 for posting their answers. Unfortunately, they didn't help me to solve my problem.

I would like to post my answer to this question.

My docker-compose.yml:

---
# Define Docker Compose version.
version: "3"

# Define all the containers.
services:
  # Frontend Container.
  frontend:
    build: ./app/frontend
    volumes:
      - ./app/frontend:/usr/src/app
    ports:
     - 3000:3000
    environment:
      NODE_ENV: development
    command: /usr/src/app/entrypoint.sh

My Dockerfile:

# Set the base image.
FROM node:10

# Create and define the node_modules's cache directory.
RUN mkdir /usr/src/cache
WORKDIR /usr/src/cache

# Install the application's dependencies into the node_modules's cache directory.
COPY package.json ./
COPY package-lock.json ./
RUN npm install

# Create and define the application's working directory.
RUN mkdir /usr/src/app
WORKDIR /usr/src/app

And last but not least entrypoint.sh:

#!/bin/bash

cp -r /usr/src/cache/node_modules/. /usr/src/app/node_modules/
exec npm start

The trickiest part here is to install the node_modules into the node_module's cache directory (/usr/src/cache) which is defined in our Dockerfile. After that, entrypoint.sh will move the node_modules from the cache directory (/usr/src/cache) to our application directory (/usr/src/app). Thanks to this the entire node_modules directory will appear on our host machine.

Looking at my question above I wanted:

• to install node_modules automatically instead of manually
• to install node_modules inside the Docker container instead of the host
• to have node_modules synchronized with the host (if I install some new package inside the Docker container, it should be synchronized with the host automatically without any manual actions

The first thing is done: node_modules are installed automatically. The second thing is done too: node_modules are installed inside the Docker container (so, there will be no cross-platform issues). And the third thing is done too: node_modules that were installed inside the Docker container will be visible on our host machine and they will be synchronized! If we install some new package inside the Docker container, it will be synchronized with our host machine at once.

The important thing to note: truly speaking, the new package installed inside the Docker container, will appear in /usr/src/app/node_modules. As this directory is synchronized with our host machine, this new package will appear on our host machine's node_modules directory too. But the /usr/src/cache/node_modules will have the old build at this point (without this new package). Anyway, it is not a problem for us. During next docker-compose up --build (--build is required) the Docker will re-install the node_modules (because package.json was changed) and the entrypoint.sh file will move them to our /usr/src/app/node_modules.

You should take into account one more important thing. If you git pull the code from the remote repository or git checkout your-teammate-branch when Docker is running, there may be some new packages added to the package.json file. In this case, you should stop the Docker with CTRL + C and up it again with docker-compose up --build (--build is required). If your containers are running as a daemon, you should just execute docker-compose stop to stop the containers and up it again with docker-compose up --build (--build is required).

If you have any questions, please let me know in the comments.

Hope this helps.

There's three things going on here:

1. When you run docker build or docker-compose build, your Dockerfile builds a new image containing a /usr/src/app/node_modules directory and a Node installation, but nothing else. In particular, your application isn't in the built image.
2. When you docker-compose up, the volumes: ['./app/frontend:/usr/src/app'] directive hides whatever was in /usr/src/app and mounts host system content on top of it.
3. Then the volumes: ['frontend-node-modules:/usr/src/app/node_modules'] directive mounts the named volume on top of the node_modules tree, hiding the corresponding host system directory.

If you were to launch another container and attach the named volume to it, I expect you'd see the node_modules tree there. For what you're describing you just don't want the named volume: delete the second line from the volumes: block and the volumes: section at the end of the docker-compose.yml file.