Node modules not found with Dockerfile and docker-compose due to bind mount

Question

So I have this NodeJS express app. This is code works:

Dockerfile

FROM node:10.16-alpine
WORKDIR /app
COPY . /app
RUN npm install
CMD ["npm", "start"]

docker-compose.yml

version: "3.7"

services:
  node-express:
    build: .
    ports: 
      - 80:3000

But for this app I want to see the live code changes. So I know that is where you can use Bind Mounts, but as soon as I add the volumes like so:

docker-compose.yml

version: "3.7"

services:
  node-express:
    build: .
    volumes: 
      - .:/app
    ports: 
      - 80:3000

It looks like the node_modules is not in the "app" directory anymore.. How can I fix this? I've worked on this for four hours, and I still can't spot the mistake!

Error

HijackManiac:webserver hijackmaniac$ docker-compose up
Creating network "webserver_default" with the default driver
Building node-express
Step 1/5 : FROM node:10.16-alpine
 ---> a298c79121d9
Step 2/5 : WORKDIR /app
 ---> Running in 9b99df0f54ba
Removing intermediate container 9b99df0f54ba
 ---> 48f9b606b32d
Step 3/5 : COPY . /app
 ---> 1f29dc735dc7
Step 4/5 : RUN npm install
 ---> Running in 81225f56a9fd
npm WARN [email protected] No description
npm WARN [email protected] No repository field.

added 106 packages from 130 contributors and audited 202 packages in 3.344s
found 0 vulnerabilities

Removing intermediate container 81225f56a9fd
 ---> 2985dc77bc12
Step 5/5 : CMD ["npm", "start"]
 ---> Running in 271ab42687ce
Removing intermediate container 271ab42687ce
 ---> 38a39768792e

Successfully built 38a39768792e
Successfully tagged webserver_node-express:latest
WARNING: Image for service node-express was built because it did not already exist. To rebuild this image you must use `docker-compose build` or `docker-compose up --build`.
Creating webserver_node-express_1 ... done
Attaching to webserver_node-express_1
node-express_1  | 
node-express_1  | > [email protected] start /app
node-express_1  | > node src/app.js
node-express_1  | 
node-express_1  | internal/modules/cjs/loader.js:638
node-express_1  |     throw err;
node-express_1  |     ^
node-express_1  | 
node-express_1  | Error: Cannot find module 'express'
node-express_1  |     at Function.Module._resolveFilename (internal/modules/cjs/loader.js:636:15)
node-express_1  |     at Function.Module._load (internal/modules/cjs/loader.js:562:25)
node-express_1  |     at Module.require (internal/modules/cjs/loader.js:690:17)
node-express_1  |     at require (internal/modules/cjs/helpers.js:25:18)
node-express_1  |     at Object.<anonymous> (/app/src/app.js:2:17)
node-express_1  |     at Module._compile (internal/modules/cjs/loader.js:776:30)
node-express_1  |     at Object.Module._extensions..js (internal/modules/cjs/loader.js:787:10)
node-express_1  |     at Module.load (internal/modules/cjs/loader.js:653:32)
node-express_1  |     at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
node-express_1  |     at Function.Module._load (internal/modules/cjs/loader.js:585:3)
node-express_1  | npm ERR! code ELIFECYCLE
node-express_1  | npm ERR! errno 1
node-express_1  | npm ERR! [email protected] start: `node src/app.js`
node-express_1  | npm ERR! Exit status 1
node-express_1  | npm ERR! 
node-express_1  | npm ERR! Failed at the [email protected] start script.
node-express_1  | npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
node-express_1  | npm WARN Local package.json exists, but node_modules missing, did you mean to install?
node-express_1  | 
node-express_1  | npm ERR! A complete log of this run can be found in:
node-express_1  | npm ERR!     /root/.npm/_logs/2019-06-04T23_55_20_327Z-debug.log
webserver_node-express_1 exited with code 1

See working tree:

Before I added the volume in the docker-compose.yml, the container runs succesfully. This is the structure:

Answer 1

You need to either modify your project structure moving every editable code inside a folder let's say src, or update your Dockerfile to move node_modules a directory upper.

As we know, when Node can't find node_modules in the current directory, it starts looking for it in the parent directory, so we take advantage of it.

a Dockerfile similar to this will solve your problem.

FROM node:10.16-alpine
WORKDIR /node
COPY package.json package-lock.json ./

RUN npm install
WORKDIR /node/app
COPY . .

CMD ["npm", "start"]

Please make sure to make appropriate changes to the docker-compose.yml too (directory structure has changed)

Answer 2

When you mount the volume of your project into the container working directory your overriding any changes you've made since the original copy/add in your Dockerfile with what is in your local project directory. In this case that means the node_modules folder. The easiest way I've found to fix this problem is to not mount the entire project directory, but just a subfolder that has my source code.