Question 278606 in Ubuntu Question posted in
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Ubuntu – I defined a static IP in the docker compose file but I can only access it on 0.0.0.0

I’m creating a docker-compose file to be able to access different containers over an IP on my machine. My Docker compose file is the following:

version: '3.7'

services:
  apache-php8:
    build: ./apache-php8
    volumes:
     - ../webphp8:/var/www/html/web
    ports:
     - 80:80    
    networks:
      web_net:
        ipv4_address: 192.168.100.4

  mysql:
    image: mysql:5.7    
    restart: always
    volumes:
      - ../data:/var/lib/mysql
    ports:
     - 3306:3306
    environment:
      MYSQL_ROOT_PASSWORD: password
      MYSQL_DATABASE: test
      MYSQL_USER: test
      MYSQL_PASSWORD: test
    networks:
      web_net:
        ipv4_address: 192.168.100.3

networks:
  web_net:
    driver: bridge
    driver_opts:
      com.docker.network.enable_ipv6: "false"
    ipam:
      driver: default
      config:
      - subnet: 192.168.100.0/24
        gateway: 192.168.100.1

I’d expect being able to acces the code on the machine on the 192.168.100.4, as that is the IP that I defined for the server, however, I only access to it in the 0.0.0.0 IP. I’m in an Ubuntu host machine, if that matters.

Do you know why is that, and what I have to do to change it to access the server on 192.168.100.4?

Tags:

2

Answers


  1. 0

    When you define ports in a docker compose file like:

    ports:
 - 80:80

    It binds the container’s port 80 to the host’s port 80 on all available interfaces, which typically includes 127.0.0.1 (localhost) and 0.0.0.0 (all IP addresses on the local machine).

    That is why you are able to access your services via 0.0.0.0 or localhost.

    However, docker does not bind container IPs to the host system directly. IP addresses assigned within a docker compose file via ipv4_adresses are internal. to the docker bridge network (web_net in this case) and not exposed to the host network interface directly.

    If you really want to access the container using 192.168.100.4 from your host machine, there are a few things you can do:

    1. Use the host network: This is generally a bad idea because it bypasses the managed docker network, but it would allow you to bind your services directly yo the host’s network
    2. Custom Host Entry: You could add an entry to the host’s /etc/hosts file that maps 192.168.100.4 back to localhost.
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  2. 0

    Do you know why is that, and what I have to do to change it to access the server on 192.168.100.4?

    Containers within Docker have their own virtual network within your host machine (i.e., the physical laptop or desktop you are using). Within this virtual network, the containers (mysql and apache-php8) talk to each other using the IP addresses you defined (the 192.168.100.0/24 subnet). Therefore the mysql container (and any other container you create in the cluster) will reach apache-php8 via either the IP address (192.168.100.4) or the apache-php8 hostname. These 192.168.100.# IP addresses are not available to you from the host machine, but must be exposed.

    Exposing your apache-php8 container’s ports are accomplished as you have already done (ports: - 80:80), and that allows you to access apache-php8 port 80 via your laptop’s localhost hostname or 127.0.0.1 loopback IP address. If you wish to access apache-php8 via the 192.168.100.4 IP address, you would need to first get into a container on that virtual network and then connect to 192.168.100.4 as needed (though there are not many human/practical uses for that — it’s generally so that containers/services can talk to each other in the network)

    On a side note, I have seen instances where a web service (or some other service) was started up in a container, but only listening on 127.0.0.1 or the container IP address. If this is the case, only the container itself (127.0.0.1) or other containers with access to the virtual network (192.168.100.*) could talk to that service. The only way to make it available to the host machine is by starting the application/service (Apache, MySQL, etc.) with listen on '*' or 0.0.0.0, which allows incoming traffic to all of that container’s network addresses.

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