yarn-Dockerfile

# build stage called build-env
FROM node:lts-alpine as build-env 

#declare environment variable to build stage
ENV NODE_ENV=production

#add all file in the context to /opt/app (same as copy but it has extra feature)
ADD . /opt/app

#change the image base directory
WORKDIR /opt/app

RUN \
  yarn install && \
  yarn build

#main stage
FROM node:lts-alpine
WORKDIR /opt/app
# --from is used to tell the docker to get data from build stage called build-env
COPY --from=build-env /opt/app/build /opt/app/build

RUN npm install -g serve

#run this command when running a container from this image (same like entrypoint but it has some different feature)
CMD ["serve","-s","build"]