Local nodejs module not being found by docker - node.js

Question

I have a nodejs module called my-common that contains a couple of js files. These js files export functions that are used throughout a lot of other modules.
My other module (called demo) contains a dependency to the the common module like this:
"dependencies": {
"my-common": "file:../my-common/",
}
When I goto the demo directory and run npm start it works fine. I then build a docker image using the following Dockerfile:
FROM node:8
ENV NODE_ENV=production
WORKDIR /usr/src/app
COPY package*.json ./
RUN npm install --only=production
COPY . .
EXPOSE 3000
CMD [ "npm", "start" ]
When I start the image I get an error that my-common can not be found. I'm guessing that the my-common module isn't being copied into the node_modules directory of the demo module.
I have tried npm link however I think it's a really really really bad idea to need sudo permission to install a global module because this could cause problems on other systems.
I have tried npm install my-common/ in the root directory and that installs the module into my HOME_DIR/node_modules however that isn't installed either into the docker container.
Everywhere I look there doesn't seem an answer to this very simple question. How can I fix this?

Answer 1

So, I see a couple different things.
When Docker runs npm install --only=production in the image, Docker sees file:../my-common/ and looks at the parent directory of the WORKDIR of the Docker image, which is /usr/src/app. Since nothing besides package.json has been copied into the image at that point, it can't find the module. If you want to install everything locally and then move it into the image, you can do that by removing the npm install --only=production command from the Dockerfile, and make sure your .dockerignore file doesn't ignore the node_modules directory.
If you want to install modules in the image, you need to specifically copy the my-common directory into the docker image. However, Docker doesn't allow you to copy something from a parent directory into a image. Any local content has to be in the context of the Dockerfile. You have a couple options:
Option 1: Move my-common/ into the root of your project, update your Dockerfile to copy that folder and update package.json to point to the correct location.
Dockerfile:
FROM node:8
ENV NODE_ENV=production
WORKDIR /usr/src/app
COPY my-common/ ./
COPY package*.json ./
RUN npm install --only=production
COPY . .
EXPOSE 3000
CMD [ "npm", "start" ]
package.json:
"dependencies": {
"my-common": "file:./my-common/",
}
Option 2: Move the context of the Docker image up one directory. By this I mean move the Dockerfile to the same level as my-common directory and update your Dockerfile and package.json to reflect that change.
Dockerfile:
FROM node:8
ENV NODE_ENV=production
WORKDIR /usr/src/app
RUN mkdir my-common
COPY ./my-common ./my-common
COPY ./<projectName>/package*.json .
RUN npm install --only=production
COPY ./<projectName> .
EXPOSE 3000
CMD [ "npm", "start" ]
package.json:
"dependencies": {
"my-common": "file:./my-common/",
}