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I’ve been tasked with dockerizing our Node app at work. When it comes to node_modules, I’m in a bit of a disagreement with our lead dev.

He is advocating for something like this in the dockerfile. His reasoning is that the docker image will be more deterministic, and on that point I don’t entirely disagree with him.

COPY node_modules ./

I am advocating for something like this. My reasoning.. that’s essentially how everyone on the internet says to do it, including the Node docs and the Docker docs. I wish I was arguing from a technical perspective, but I just can’t seem to find anything that specifically addresses this.

COPY package*.json ./
RUN npm install

So who is right? What would be the downsides associated with the first option?

J. Munson
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1 Answers1

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I'd almost always install Node packages from inside the container rather than COPYing them from the host (probably via RUN npm ci if I was using npm).

If the host environment doesn't exactly match the container environment, COPYing the host's node_modules directory may not work well (or at all). The most obvious case of this using a MacOS or Windows host with a Linux container, where if there are any C extensions or other binaries they just won't work. It's also conceivable that there would be if the Node versions don't match exactly. Finally, and individual developer might have npm installed an additional package or a different version, and the image would vary based on who's building it.

Also consider the approach of using a multi-stage build to have both development and production versions of node_modules; that way you do not include build-only tools like the tsc Typescript compiler in the final image. If you have two different versions of node_modules then you can't COPY a single tree from the host, you must install it in the Dockerfile.

FROM node AS build
WORKDIR /app
COPY package*.json .
RUN npm ci
COPY . .
RUN npm install

FROM node
WORKDIR /app
COPY package*.json .
ENV NODE_ENV=production
RUN npm ci
COPY --from=build /app/build /app/build
CMD ["node", "/app/build/index.js"]
David Maze
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