Docker automatically rerun npm install on package.json change

Question

I'm trying to set up development containers for a node.js project so that my local source files are shared with the guest (so I can dnsmasq wildcard requests to a local domain over port 80, but I guess that's irrelevant to the question). When I make a change locally, the node process in the container is restarted:

Dockerfile:

FROM node:8

# Install app dependencies
RUN npm install -g nodemon
COPY package.json /tmp/package.json
RUN cd /tmp && npm install --production

NODE_PATH=/tmp/node_modules
WORKDIR /app

EXPOSE 8080
EXPOSE 9229

CMD nodemon --inspect index.js

docker-compose.json (truncated):

version: '3.3'
services:
    app:
        build: .
        container_name: 'my-app'
        restart: unless-stopped
        ports:
            - 8080:8080
            - 9229:9229
        volumes:
            - .:/app

Because the node_modules are installed in the Dockerfile, every time I add a package to packages.json, I have to manually re-build the container:

docker-compose stop
docker-compose build
docker-compose up -d

I could set up a watch for this using inotify, but I don't like to stop the entire stack (including other services defined there).

Is it possible to have this logic inside the container, and re-run npm install every time package.json is changed?

Answer 1

Is it possible to have this logic inside the container, and re-run npm install every time package.json is changed?

It is not fully clear to me, if your changes in package.json are done on host or in docker container in /tmp/ directory. I guess you modify a file on host since you have other project files there.

If you modify package.json in other location than /tmp/ in your container, you need to manually copy new version of package.json to /tmp in container

docker cp "location/of/package.json" "containername":/tmp/

then you just enter the container and install dependencies.

docker exec -it containername bash
cd /tmp/
npm install

Is it possible to have this logic inside the container, and re-run npm install every time package.json is changed?

You could pass logic described above to simple bash script. Then you can run some watcher (for example nodemon) to observe package.json and run the script after file change. Maybe it would be also good idea to pass big delay so it doesn't try to install a module before you even type full name of it. But in most situations I guess you just use npm command instead of typing name of the module manually.