Haproxy won't work with docker

Help!
1

Hi everyone, I’m new on using haproxy and Docker and I’m having trubles setting up a web app with Docker-compose.
I am using an Node.js app listening on port 8001 and it connects on a local database mongodb on port 27017. I have created a Docker compose file for configuring a Docker environment with 3 serves of the app, the DB and the haproxy server.

version: “3”
services:
   app1:
     container_name: app1
     restart: always
     build: .
     ports:
       - “81:8001”
     links:
       - mongo
     networks:
       - my-net
   app2:
     container_name: app2
     restart: always
     build: .
     ports:
       - “82:8001”
     links:
       - mongo
     networks:
       - my-net
    app3:
      container_name: app3
      restart: always
      build: .
      ports:
        - “83:8001”
      links:
        - mongo
      networks:
        - my-net
    mongo:
      container_name: mongo
      image: mongo 
      ports:
        - “27017:27017”
      networks:
        - my-net
    haproxy:
      build: ./haproxy
      container_name: haproxy
      links:
        - app1
        - app2
        - app3
      ports:
        - “80:80”
        - “8404:8404”
      networks:
        - my-net
    networks: 
      my-net:
        name: my-net
        driver: bridge

the docker files for the haproxy is this:

FROM haproxytech/haproxy-alpine:2.4
COPY haproxy.conf /usr/local/etc/haproxy/haproxy.conf

and the docker file for the apps is the following:

FROM node:13-alpine

RUN mkdir -p /home/app

COPY ./nosql_practica4_bbdd-main /home/app

WORKDIR /home/app

RUN npm install

RUN npm run seed

CMD [“npm”, “start”]

EXPOSE 8001

The app is working if I type the ports on the browser but the haproxy isn’t working and on the logs it shows this error:
[ALERT] (8) : backend ‘app’ has no server available! docker

the haproxy.conf is the following:

global
  stats socket /var/run/api.sock user haproxy group haproxy mode 660 level admin expose-fd listeners
  log stdout format raw local0 info

defaults
  log global
  mode http
  option httplog
  option dontlognull
  timeout connect 5000
  timeout client 10000
  timeout server 10000
   
frontend balancer
  bind 0.0.0.0:80
  mode http
  default_backend apps

backend apps
  mode http
  balance roundrobin
  server app1 app1:8001 check
  server app2 app2:8001 check
  server app3 app3:8001 check

anyone can help me understand what I have done wrong?

2

I think you should target the host’s ports instead of the container’s ports in the haproxy.cfg, but i did not test it

  server app1 app1:81 check
  server app2 app2:82 check
  server app3 app3:83 check
3

I tried it but still not working. It must be some configuration problem within the docker network.
thank you!