Docker and private modules

To install private npm packages in a Docker container, you will need to use Docker build secrets.

Background: runtime variables

You cannot install private npm packages in a Docker container using only runtime variables. Consider the following Dockerfile:

FROM node

COPY package.json package.json
RUN npm install

# Add your source files
COPY . .
CMD npm start

Which will use the official Node.js image, copy the package.json into our container, installs dependencies, copies the source files and runs the start command as specified in the package.json.

In order to install private packages, you may think that we could just add a line before we run npm install, using the ENV parameter:

ENV NPM_TOKEN=00000000-0000-0000-0000-000000000000

However, this doesn't work as you would expect, because you want the npm install to occur when you run docker build, and in this instance, ENV variables aren't used, they are set for runtime only.

Instead of run-time variables, you must use Docker build secrets.

Update the Dockerfile

The Dockerfile that takes advantage of this has a few more lines in it than the earlier example that allows us to use your global .npmrc and the access token created when running npm login command (if you haven't run it already - do so before moving on).

# https://docs.npmjs.com/docker-and-private-modules
FROM node:18

ENV APP_HOME="/app"

WORKDIR ${APP_HOME}

COPY package*.json ${APP_HOME}/

RUN --mount=type=secret,id=npmrc,target=/root/.npmrc npm install

COPY . ${APP_HOME}/

CMD npm start

This will configure your Dockerfile to receive .npmrc file via build secrets, that will leave no trace after npm dependency installation is done.

Build the Docker image

To build the image using the above Dockerfile and the npm authentication token, you can run the following command. Note the . at the end to give docker build the current directory as an argument.

docker build . -t secure-app-secrets:1.0 --secret id=npmrc,src=$HOME/.npmrc

This will build the Docker image with the access token coming from your global .npmrc file received via build secrets, so you can run npm install inside your container as the current logged-in user.

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Last edited by matzar on March 16, 2023