Docker not installing node_modules with yarn

Question

I am running a Ruby on Rails app with Webpacker using Yarn and trying to run this on Docker via Docker Compose. When I run docker compose build it looks like it runs successfully, but the node_modules folder is nowhere to be found and I can't use any node packages. I tried adding - /app/node_modules to the volumes as suggested in other posts but to no avail.

FROM ruby:3.0.0
RUN bundle config --global frozen 1

WORKDIR /app

COPY Gemfile Gemfile.lock ./
RUN bundle install


COPY . .

RUN curl -fsSL https://deb.nodesource.com/setup_16.x | bash -
RUN apt-get install -y nodejs
RUN npm install --global yarn
RUN yarn install

docker-compose.yml

version: "3.9"
services:
  web:
    build: .
    ports:
      - "3000:3000"
    command: "rails server -b 0.0.0.0"
    volumes:
      - ./:/app
      - /app/node_modules
  db:
    image: "postgres:13"
    ports:
      - "5432:5432"
    volumes:
      - ./pgdata:/var/lib/postgresql/data
    environment:
      - POSTGRES_USER=user
      - POSTGRES_PASSWORD=password

Answer 1

Remove volumes from web service or mount only what you exactly need, not everything in the directory.
If you're mounting you're local directory, then it overwrite everything inside the container.

A good practice is to create .dockerignore file as well. Put there what shouldn't be copied from host machine like node_modules