How to Optimize Docker File for React App - node.js

Question

Currently I have the docker file, which runs a non-optimized react app (it says 'Note that the development build is not optimized. To create a production build, use npm run build.'). The docker file is:
FROM node:16
# A directory within the virtualized Docker environment
# Becomes more relevant when using Docker Compose later
WORKDIR /usr/src/app
# Copies package.json and package-lock.json to Docker environment
COPY package*.json ./
# Installs all node packages
RUN npm install
# Copies everything over to Docker environment
COPY . .
# Uses port which is used by the actual application
EXPOSE 3000
# Finally runs the application
CMD [ "npm", "start" ]
With the above I can hit my service at http://localhost:3000/ .
I tried the following (from https://medium.com/geekculture/dockerizing-a-react-application-with-multi-stage-docker-build-4a5c6ca68166) but I could not access my service:
The docker file I tried is
# pull official base image
FROM node:16 AS builder
# set working directory
WORKDIR /app
# install app dependencies
#copies package.json and package-lock.json to Docker environment
COPY package.json ./
# Installs all node packages
EXPOSE 3000
RUN npm install
# Copies everything over to Docker environment
COPY . ./
RUN npm run build
#Stage 2
#######################################
#pull the official nginx:1.19.0 base image
FROM nginx:1.19.0
#copies React to the container directory
# Set working directory to nginx resources directory
WORKDIR /usr/share/nginx/html
# Remove default nginx static resources
RUN rm -rf ./*
# Copies static resources from builder stage
COPY --from=builder /app/build .
EXPOSE 3000
# Containers run nginx with global directives and daemon off
ENTRYPOINT ["nginx", "-g", "daemon off;"]
Does anyone know what to do to fix this (or how to create an optimized build)?

Answer 1

The root issue was that I was not aware that nginx was serving on port 80. The following docker file works and is run in the following way: docker run -p 80:80 my-ui-app
# pull official base image
FROM node:16 AS builder
# set working directory
WORKDIR /app
# install app dependencies
#copies package.json and package-lock.json to Docker environment
COPY package.json ./
# Installs all node packages
RUN npm install
# Copies everything over to Docker environment
COPY . ./
RUN npm run build
#Stage 2
#######################################
#pull the official nginx:1.19.0 base image
FROM nginx:1.19.0
#copies React to the container directory
# Set working directory to nginx resources directory
WORKDIR /usr/share/nginx/html
# Remove default nginx static resources
RUN rm -rf ./*
# Copies static resources from builder stage
COPY --from=builder /app/build .
EXPOSE 80
# Containers run nginx with global directives and daemon off
ENTRYPOINT ["nginx", "-g", "daemon off;"]