Speed up build by caching packages in Docker container

Question

I have this idea that I haven't completed yet. In a Dockerfile I have:

FROM node:10

WORKDIR /app

RUN "*cache node modules here*"
RUN e.g. npm cache add foo bar baz

COPY package.json .
RUN npm i --cache-min 9999999 --loglevel=warn

COPY . .

CMD node dist

How can I create ultra high-performance Dockerfiles by caching some Node.js modules/package before the npm install step?

Is there some trick that can do this?

Answer 1

This is out-of-the-box Docker functionality. If your Dockerfile says

FROM node:10
WORKDIR /app
COPY package.json .
RUN npm install

COPY ...

then, if the package.json hasn't changed, Docker will skip over the RUN npm install step and use the filesystem image that results from doing it.