Install node_modules inside Docker container and synchronize them with host

I have the problem with installing node_modules inside the Docker container and synchronize them with the host. My Docker’s version is 18.03.1-ce, build 9ee9f40 and Docker Compose’s version is 1.21.2, build a133471.

My docker-compose.yml looks like:

# Frontend Container.
  build: ./app/frontend
    - ./app/frontend:/usr/src/app
    - frontend-node-modules:/usr/src/app/node_modules
    - 3000:3000
    NODE_ENV: ${ENV}
  command: npm start

# Define all the external volumes.
  frontend-node-modules: ~

My Dockerfile:

# Set the base image.
FROM node:10

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

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

The trick with the external volume is described in a lot of blog posts and Stack Overflow answers. For example, this one.

The application works great. The source code is synchronized. The hot reloading works great too.

The only problem that I have is that node_modules folder is empty on the host. Is it possible to synchronize the node_modules folder that is inside Docker container with the host?

I’ve already read these answers:

  1. docker-compose volume on node_modules but is empty
  2. Accessing node_modules after npm install inside Docker

Unfortunately, they didn’t help me a lot. I don’t like the first one, because I don’t want to run npm install on my host because of the possible cross-platform issues (e.g. the host is Windows or Mac and the Docker container is Debian 8 or Ubuntu 16.04). The second one is not good for me too, because I’d like to run npm install in my Dockerfile instead of running it after the Docker container is started.

Also, I’ve found this blog post. The author tries to solve the same problem I am faced with. The problem is that node_modules won’t be synchronized because we’re just copying them from the Docker container to the host.

I’d like my node_modules inside the Docker container to be synchronized with the host. Please, take into account that I want:

  • 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)

I need to have node_modules on the host, because:

  • possibility to read the source code when I need
  • the IDE needs node_modules to be installed locally so that it could have access to the devDependencies such as eslint or prettier. I don’t want to install these devDependencies globally.

Thanks in advance.

Best answer

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.

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