Cannot finde module 'express' (node app with docker)

When you run your container with -v flag, which mean mount a directory from your Docker engine’s host into a container, will overwrite what you do in /home/Documents/node-app,such as npm install.

So you cannot see the node_modules directory in the container.

$ docker run -d -P --name web -v /src/webapp:/webapp training/webapp python app.py

This command mounts the host directory, /src/webapp, into the container at /webapp. If the path /webapp already exists inside the container’s image, the /src/webapp mount overlays but does not remove the pre-existing content. Once the mount is removed, the content is accessible again. This is consistent with the expected behavior of the mount command.

mount a host directory as a data volume.As what the docs said,the pre-existing content of host directory will not be removed, but no information about what's going on the exist directory of the container.

There is a example to support my opinion.

1. Dockerfile

   FROM alpine:latest WORKDIR /usr/src/app COPY . .

2. I create a test.t file in the same directory of Dockerfile.

3. Proving

   1. Run command docker build -t test-1 .
   2. Run command docker run --name test-c-1 -it test-1 /bin/sh,then your container will open bash.
   3. Run command ls -l in your container bash,it will show test.t file.
   4. Just use the same image.
   5. Run command docker run --name test-c-2 -v /home:/usr/src/app -it test-1 /bin/sh. You cannot find the file test.t in your test-c-2 container.

That's all.I hope it will help you.