Connecting to React docker container on port 80 - reactjs

Question

I'm trying to deploy a React app as part of a docker compose. It works fine if I deploy on port 3000, but when I use port 80, I cannot connect. If I run npm start manually, either config works fine, but I cannot access the port 80 version when running as a docker image.
I've tried adding EXPOSE 80 to the dockerfile, but it did not seem to have any effect. Can someone point out the error in my config?
Dockerfile:
FROM node:17-alpine
WORKDIR /app
ENV PATH /app/node_modules/.bin:$PATH
COPY package.json ./
COPY package-lock.json ./
RUN npm install
RUN npm install react-scripts#5.0.0 -g
COPY . .
CMD ["npm", "start"]
docker-compose.yaml
version: "3.8"
services:
solvle:
build: ./
container_name: solvle_c
ports:
- '8081:8081'
solvle_front:
build: ./solvle-front
container_name: solvle_front_c
ports:
- '80:80'
stdin_open: true
tty: true
package.json fragment
"scripts": {
"start": "set PORT=80 && react-scripts start",
"build": "react-scripts build",
"test": "react-scripts test",
"eject": "react-scripts eject"
},

Answer 1

For linux you should set port in this way:
"start": "export PORT=80 && react-scripts start"
Another solution is create a file with name .env (documentation) in the main directory and set PORT variable to desired port number:
PORT=80
One more solution.
You could use cross-env to set the port:
npm install cross-env -D
and then modify start script package.json:
"start": "cross-env PORT=80 react-scripts start",
p.s.
But for deploy react app with docker I woud recomend you to use nginx.
p.p.s.
The EXPOSE instruction in dockerfile does not actually publish the port. It functions as a type of documentation. expose documentation