exposing containers to external network as host

Question

i am not experienced working with docker and docker-compose, but atleast i know how to get a container running, below is my compose file of a simple react app boiler plate. my intention was to assign an IP to it so that i can ping it from the external.network, and also to access it without any port mapping to the host

version: "3.9"
services:
  front-web:
    build:
      context: .
      dockerfile: Dockerfile
      args:
        buildno: 1.0.0
    container_name: web-front
    domainname: fontend
    dns: 8.8.8.8
    network_mode: "host"
    hostname: alpha
    restart: unless-stopped
    stop_grace_period: 1m
    expose:
      - 4000
    tty: true
    pid: host
    stdin_open: true
    ports:
      - target: 4000
        published: 4000
        protocol: tcp
        mode: host
    networks:
      web-net:
        ipv4_address: 192.168.1.195
    volumes:
      - web-front:/app/data

    

networks:
  web-net:
    name: web-net
    driver: bridge
    
    driver_opts:
      enable_ipv4: 1
      enable_ipv6: 1
    
    ipam:
      driver: default
      config:
        - subnet: 192.168.1.1/24
          ip_range: 192.168.1.195/24
          gateway:  192.168.1.195/24

volumes:
  web-front:

the docker file of the app is below

FROM node:alpine3.16
# RUN addgroup app && adduser -SG app app
# USER app
WORKDIR /app
RUN mkdir data
EXPOSE 4000
COPY package* .
RUN npm install
COPY . .
CMD [ "npm", "start" ]

ignore the "adduser" although it also failed to workout. whenever i run docker-compose up, i get an error saying:

Attaching to web-front
Error response from daemon: failed to add interface vethcf21a7d to sandbox: error setting interface "vethcf21a7d" IP to 192.168.1.195/24: cannot program address 192.168.1.195/24 in sandbox interface because it conflicts with existing route {Ifindex: 31 Dst: 192.168.1.0/24 Src: 192.168.1.1 Gw: <nil> Flags: [] Table: 254}

i am not sure how to go about this, kindly assist

I tried changing the driver part in the Networks section from brigde to macvlan, the build would pass but again i could not ping the the container with its ip. adding external:true, makes the whole thing fail

Answer 1

Docker containers running in their own.network. If you want to talk them, then you have to setup a lot of things.

• An IP-address of your container
• A route from your host-machine ( iptables is your friend)
• Maybe a special route for all your clients (because you have to use private ip-addresses which may conflict with other.networks)

At the end... it is pretty hardcore to set this up. If you still want it, then you should ask this on https://serverfault.com/ .

It would be much easier, when you the expose port feature from docker.
When this is not possible for you, then the network: host may help you.

Answer 2

The normal way to set up external access to a container is using the Compose ports: directive. In most cases that's the only.network-related configuration you need at all; setups that try to avoid ports: are almost always more complicated.

The Dockerfile you show is a pretty typical Node application. You can omit almost all of the Compose options. I'd probably reduce this to no more than:

version: "3.8"   # newest supported by all current common Compose implementations
services:
  front-web:
    build: .     # default Dockerfile name, no args
    restart: unless-stopped
    ports:
      - "4000:4000"
    volumes:     # only because you store data in the container
      - web-front:/app/data
volumes:
  web-front:

Notice in particular that I do have a ports: line, but I've removed all of the other.network-related settings, including the IP address assignment, DNS configuration, and naming overrides.

This should achieve the stated goal of making the container accessible from other hosts, and it is the standard Docker setup. In principle it's possible to assign another IP address to your host and map the container to only that address, or use more exotic setups like a Docker macvlan.network, but these are unusual setups and much more complex.