Missing node_modules folder in mounted volume after successful npm install in Docker container

[Hazel_27Yoga]

My Setup

I’m working on a project with these components:

• frontend/ - runs a Python Flask app on port 5000 with SQLite database
• processor/ - contains app.js file that processes tasks from a queue. The Flask app communicates with this through JSON API on port 8080. This processor uses Redis and saves files to processor/data/

This issue is specifically about the processor service.

processor/Dockerfile

FROM node:0.12

WORKDIR /app

COPY package.json /app/
RUN npm install

COPY . /app/

docker-compose.yml

redis:
    image: redis
processor:
    build: ./processor
    command: npm start
    ports:
        - "8080:8080"
    volumes:
        - processor/:/app/
    links:
        - redis

The Problem

When I execute docker-compose build, everything works fine and npm packages get installed in /app/node_modules.

But running docker-compose up gives me this error:

processor_1 | Error: Cannot find module 'lodash'
processor_1 |     at Function.Module._resolveFilename (module.js:336:15)
processor_1 |     at Function.Module._load (module.js:278:25)

The node_modules directory is completely empty when the container starts. If I manually run npm install on my host machine, it works, but I want Docker to handle all dependencies.

What am I doing wrong? All required packages are listed in my package.json file.

[ameliat]

Your volume mapping is wiping out the entire /app directory at runtime, including the node_modules that got installed during the build. I hit this exact issue last month with a React app. Instead of mounting the whole processor directory, just mount the specific files you need to change during development: yaml volumes: - ./processor/app.js:/app/app.js - ./processor/package.json:/app/package.json - ./processor/data:/app/data This keeps your node_modules intact while letting you edit your code. You’ll need to map each file or directory individually, but you get precise control over what syncs.

[Stella_Dreamer]

Yeah, classic Docker volume issue. Your host folder’s masking the container’s node_modules at runtime, even though the build worked fine. Add node_modules to a .dockerignore file in your processor directory - stops it from getting copied over from the host during mounting.

[Nova56]

Your volume mount is overriding the node_modules directory that Docker creates during the build. When you mount processor/:/app/, it replaces everything in /app with your local processor/ folder - which doesn’t have the installed dependencies.

I hit this same issue last year with a Node app. Fix it by changing your docker-compose.yml volumes section:

volumes:
    - processor/:/app/
    - /app/node_modules

That second line creates an anonymous volume for node_modules so your host directory can’t overwrite it. You’ll keep all the dependencies from the build but still see your code changes in the container.