DockerfileのARGはFROMに対しても使える

よく考えれば当たり前なのかもしれないが最近気付いたのでメモ

ARGで処理系のバージョン等を設定しておいてFROMにそれを埋め込めばmulti-stage buildを使う時にバージョンを一元管理できたりと色々便利そう

ARG RUBY_VERSION=2.6.2
ARG RAILS_ENV=production

FROM ruby:${RUBY_VERSION}-alpine AS node_modules
WORKDIR /opt/project
RUN apk add --no-cache --update nodejs yarn
ADD bin/yarn /opt/project/bin/
ADD package.json yarn.lock /opt/project/
ENV PATH=/opt/project/bin:${PATH}
RUN yarn install


FROM ruby:${RUBY_VERSION}-alpine AS bundle
WORKDIR /opt/project
RUN apk add --no-cache --update build-base mariadb-dev
ADD bin/bundle /opt/project/bin/
ADD .ruby-version .gemrc Gemfile Gemfile.lock /opt/project/
ENV PATH=/opt/project/bin:${PATH}
RUN \
if [ "${RAILS_ENV}" = "production" ]; then \
  bundle install --jobs 8 --without development test --deployment; \
else \
  bundle install --jobs 8 --without production --path vendor/bundle; \
fi


FROM ruby:${RUBY_VERSION}-alpine
WORKDIR /opt/project
RUN apk add --no-cache --update mariadb-dev tzdata nodejs yarn
COPY --from=bundle ${BUNDLE_APP_CONFIG} /opt/project/.bundle
COPY --from=bundle /opt/project/vendor/bundle /opt/project/vendor/bundle
COPY --from=node_modules /opt/project/node_modules /opt/project/node_modules
ADD . /opt/project/api
ENV RAILS_ENV=${RAILS_ENV}
ENV BUNDLE_APP_CONFIG=/opt/project/.bundle
ENV PATH=/opt/project/bin:${PATH}
ENV RAILS_SERVE_STATIC_FILES=true
RUN webpack
EXPOSE 3000
ENTRYPOINT ["rails"]
CMD ["server", "-b", "0.0.0.0"]