Multi-stage builds is a feature that was added in Docker v17.05. It allows you to use multiple FROM instructions to define multiple images as stages inside a single Dockerfile.

You can extract artifacts from the previous stage and add them to the next stage in a single instruction (and thus a single layer).

In our case, we can define two stages – one for building our application, and the second one that just copies the dist and node_modules directory and specifies the CMD instruction:

FROM node:8-alpine as builder
USER node
WORKDIR /home/node

COPY --chown=node:node . .
RUN ["yarn"]
COPY --chown=node:node . .
RUN ["yarn", "run", "build"]
RUN find . ! -name dist ! -name node_modules -maxdepth 1 -mindepth 1 -exec rm -rf {} \;

FROM node:8-alpine
USER node
WORKDIR /home/node
COPY --chown=node:node --from=builder /home/node .
CMD ["node", "dist/index.js"]

We use the as keyword to name our stage, and refer to them in the COPY instructions using the --from flag.

Now, if we build this using Dockerfile, we end up with two images:

$ docker images
REPOSITORY    TAG      IMAGE ID        CREATED         SIZE
hobnob        0.1.0    5268f2a4176b    5 seconds ago   122MB
<none>        <none>   f722d00c2dbf    9 seconds ago   210MB

The one without a name, <none>, represents the first stage, and the hobnob:0.1.0 image is the second stage. As you can see, our image is now only 122 MB, but we still benefited from our multi-layer Dockerfile and caching.