Node modules missing from mounted volume after successful npm install in Docker container

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1

I’m having trouble with my Docker setup where npm packages get installed during the build process but disappear when I mount a volume.

My project structure includes the following:

  • backend/ - This is a Python Flask app that runs on port 5000 and uses SQLite.
  • processor/ - This is a Node.js service that has an app.js file to handle queue processing, communicates through a JSON API on port 8080, utilizes Redis for caching, and saves files in the processor/assets/ directory.

This question is specifically about the processor service.

processor/Dockerfile:

FROM node:10

WORKDIR /app

COPY package.json /app/
RUN npm install

COPY . /app/

docker-compose.yml:

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

Upon running docker-compose build, everything works as it should and all dependencies are installed in /app/node_modules as expected. I can confirm this as I see the installation output:

npm WARN package.json [email protected] No description

> [email protected] install /app/node_modules/html-pdf/node_modules/puppeteer
> node install.js

<output continues>

However, when I run docker-compose up, I encounter a module error:

processor_1 | Error: Cannot find module 'lodash'
processor_1 |     at Function.Module._resolveFilename (module.js:548:15)
processor_1 |     at Function.Module._load (module.js:475:25)
processor_1 |     at Module.require (module.js:597:17)
processor_1 |     at require (module.js:613:17)
processor_1 |     at Object.<anonymous> (/app/app.js:2:18)
processor_1 |     at Module._compile (module.js:649:30)
processor_1 |     at Object.Module._extensions..js (module.js:660:10)
processor_1 |     at Module.load (module.js:565:32)
processor_1 |     at tryModuleLoad (module.js:505:12)
processor_1 |     at Function.Module._load (module.js:497:3)

It appears that the /app/node_modules folder is completely empty in both the Docker container and on the host machine.

When I run npm install on my host device manually, everything then works well. However, I would prefer that Docker handle all dependencies without requiring me to perform local installations.

What could be causing this issue? All necessary packages are accurately listed in my package.json file.

2

Your volume mapping is wiping out the /app/ directory, including the node_modules that Docker built. When you mount ./processor/:/app/, it replaces everything in the container with your local folder - but your local folder doesn’t have node_modules since you haven’t run npm install there. Fix it by excluding node_modules with an anonymous volume, or restructure your Dockerfile to install dependencies after copying files. You could also just bind mount specific subdirectories instead of the whole project root.

3

Classic volume mount issue - your ./processor/:/app/ volume’s overriding the node_modules installed during build. Try adding a named volume for node_modules or move the COPY before npm install so it doesn’t get wiped.

4

I encountered a similar issue when working with a React app. The problem lies in how Docker Compose handles volumes: when you mount ./processor/:/app/, it completely replaces the contents of /app/ with what’s in your local folder, which does not include node_modules. To solve this, you can either add node_modules:/app/node_modules as an anonymous volume in your docker-compose.yml to preserve that directory or modify your Dockerfile to copy all necessary files before running npm install. I recommend using the anonymous volume approach to maintain your current setup while preventing the loss of node_modules.