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Troubleshooting HAProxy Access Issue in Docker-Compose Setup

I’m new to Docker and have been trying to get a simple docker-compose setup working However, I’m facing an issue:
although I can directly access the web application on the exposed port 82, I can’t seem to reach it via HAProxy on the exposed port 81. I’m currently using Docker version 25.0.3.
Can anyone help me figure out what I might be missing in my configuration?

version: '3'
services:
  webapp:
    image: httpd
    ports:
     - 82:80

   lb:
     image: 'dockercloud/haproxy:latest'
     volumes:
        - /var/run/docker.sock:/var/run/docker.sock
     links:
       - webapp
     ports:
      - 81:80
Tags:

2

Answers


  1. 0

    Your setup looks like this:

           Internet
           |
          [81]
       HAProxy
           |
          [80]
        Web App
           |
          [82]
    • Requests come in on port 81 (HAProxy), which should then forward them to the web application listening on port 80 inside its container.
    • The web app container maps port 80 internally to port 82 externally.

    Try the following docker-compose.yml file for a proper networking and communication between the webapp and lb services:

    version: '3'
services:
  webapp:
    image: httpd
    ports:
      - 82:80
    networks:
      - webnet

  lb:
    image: 'dockercloud/haproxy:latest'
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    ports:
      - 81:80
    depends_on:
      - webapp
    networks:
      - webnet

networks:
  webnet:

    As suggested, the links: option is obsolete and not necessary for modern Docker networking. Containers in the same network can discover and communicate with each other by service names.

    This defines a custom network webnet and assigned both services to it. That makes sure they can communicate using the service name as the hostname.
    Make sure your HAProxy configuration within the dockercloud/haproxy container is correctly set up to route traffic to the webapp service. HAProxy needs to know the correct service name and port to forward requests appropriately.

    docker exec -it [container_id_or_name] /bin/sh
cat /etc/haproxy/haproxy.cfg
...
# you should see a backend section like:
backend http_back
    balance roundrobin
    server webapp webapp:80 check

    And check that HAProxy is configured to listen on 0.0.0.0:80 or *:80 to make sure it accepts connections from all IP addresses, at least for testing.

    Still not working, but when I checked haproxy.cfg backend section, it looks like this:

    backend app 
balance roundrobin 
server app1 127.0.0.1:5001 check 
server app2 127.0.0.1:5002 check 
server app3 127.0.0.1:5003 
check server app4 127.0.0.1:5004 check

    and no other containers are currently active

    I tried to use port 5001 instead of 81, but still no luck

    If auto-discovery is failing and you have specific routing needs, consider manually specifying your HAProxy configuration. You can mount a custom haproxy.cfg file into a standard HAProxy container, replacing dockercloud/haproxy for debugging purposes:

    version: '3'
services:
  webapp:
    image: httpd
    networks:
      - webnet

  haproxy:
    image: haproxy:latest
    volumes:
      - ./haproxy.cfg:/usr/local/etc/haproxy/haproxy.cfg:ro
    ports:
      - "81:80"
    networks:
      - webnet

networks:
  webnet:

    In haproxy.cfg, explicitly define the backend to point to your webapp service, making sure it matches the service name and port within the Docker network:

    backend webapp_backend
    balance roundrobin
    server webapp webapp:80 check
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  2. 0

    I think there are some issues with your docker file.

    1. links is no more used and is dropped by dockers now depends_on is to be used.
    2. Your docker should look something as below
    services:
  webapp:
    image: httpd
    networks:
      - mynetwork

  lb:
    image: haproxy:latest
    volumes:
      - ./haproxy.cfg:/usr/local/etc/haproxy/haproxy.cfg:ro
    ports:
      - "81:80"
    networks:
      - mynetwork

networks:
  mynetwork

    Additionally you may be required to use a custom haproxy.cfg

    
backend webapp_backend
    balance roundrobin
    server webapp webapp:80 check
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