This is great! Thanks for sharing. I can recommend a small change to get most out of docker caching and reducing docker build times to the maximum extent.

In the "builder" you only need package.json and package-lock.json files to install dependencies. The rest of the sources can be copied in the "scratch-node" image. This would make caching work till the last line where only code changes are included. Code is modified much more frequently than dependencies.

You sample can look like this:

FROM node as builder

WORKDIR /app

COPY package.json package-lock.json index.js ./

RUN npm install --prod

FROM astefanutti/scratch-node

COPY --from=builder /app/node_modules /node_modules

COPY ./ ./

ENTRYPOINT ["./node", "index.js"]