Optimize Dockerfile - node.js

Question

Our frontends have such Dockerfile:
FROM node:13.12.0
RUN apt-get update && apt-get install -y --no-install-recommends \
apt-utils \
git \
xvfb \
libgtk-3-0 \
libxtst6 \
libgconf-2-4 \
libgtk2.0-0 \
libnotify-dev \
libnss3 \
libxss1 \
libasound2 \
tzdata && \
rm -rf /var/lib/apt/lists/* && \
ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && \
echo $TZ > /etc/timezone
COPY ./docker-entrypoint.sh /docker-entrypoint.sh
ENTRYPOINT ["/docker-entrypoint.sh"]
WORKDIR /code
COPY ./ /code
RUN npm set registry <registry-url> && \
npm cache clean --force && npm install && npm run bootstrap
As far as I can see it is not optimized because code copying happens before dependencies installation, right? And a better way would be to copy package.json and install dependencies first and then code copying? Something like this:
FROM node:13.12.0
RUN apt-get update && apt-get install -y --no-install-recommends \
apt-utils \
git \
xvfb \
libgtk-3-0 \
libxtst6 \
libgconf-2-4 \
libgtk2.0-0 \
libnotify-dev \
libnss3 \
libxss1 \
libasound2 \
tzdata && \
rm -rf /var/lib/apt/lists/* && \
ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && \
echo $TZ > /etc/timezone
COPY ./docker-entrypoint.sh /docker-entrypoint.sh
WORKDIR /code
COPY package*.json ./
RUN npm set registry <registry-url> && \
npm cache clean --force && npm install && npm run bootstrap
COPY ./ /code
ENTRYPOINT ["/docker-entrypoint.sh"]

Answer 1

I think one of the most important thing related to Dockerfile optimization is to put the elements that might be changing in future versions of your container, the latest cause in case of any change on the code part, being the latest will not force recreation on other layers.
I think that's the reason for the Dockerfile to look like it does in your first example
There are other considerations regarding Dockerfile optimization that you can read for example here:
https://linuxhint.com/optimizing-docker-images/

Answer 2

The hadolint/hadolint Dockerfile linter is a good starting point. Linting your Dockerfile using the Haskell Dockerfile Linter i.e. docker run --rm -i hadolint/hadolint < Dockerfile:
/dev/stdin:5 SC2086 info: Double quote to prevent globbing and word splitting.
/dev/stdin:5 DL3008 warning: Pin versions in apt get install. Instead of `apt-get install <package>` use `apt-get install <package>=<version>`
... after fixing the issues and sorting the packages alphanumerically following the best practices with a couple of minor modifications your Dockerfile might look like:
FROM node:13.12.0
ARG NPM_REGISTRY
RUN apt-get update && \
apt-get install -y --no-install-recommends \
apt-utils=1.4.11 \
git=1:2.11.0-3+deb9u7 \
libasound2=1.1.3-5 \
libgconf-2-4=3.2.6-4+b1 \
libgtk2.0-0=2.24.31-2 \
libgtk-3-0=3.22.11-1 \
libnotify-dev=0.7.7-2 \
libnss3=2:3.26.2-1.1+deb9u2 \
libxss1=1:1.2.2-1 \
libxtst6=2:1.2.3-1 \
tzdata=2021a-0+deb9u1 \
xvfb=2:1.19.2-1+deb9u7 && \
rm -rf /var/lib/apt/lists/* && \
ln -snf "/usr/share/zoneinfo/$TZ" /etc/localtime && \
echo "$TZ" > /etc/timezone
COPY docker-entrypoint.sh /docker-entrypoint.sh
WORKDIR /code
COPY package*.json ./
RUN npm set registry "${NPM_REGISTRY}" && \
npm cache clean --force && \
npm install && \
npm run bootstrap
COPY . .
ENTRYPOINT ["/docker-entrypoint.sh"]
Note: the minor changes are by preference, i.e. COPY . . to COPY from the context into the /code directory which is set by the WORKDIR instruction.
Build the image passing the NPM_REGISTRY as a build arg i.e.: docker build --rm --build-arg NPM_REGISTRY=https://yarn.npmjs.org -t so:66493910 .