Docker Image Tags:

• latest
• 3
• 3.x.x

Docker image to forward TCP and UDP traffic to the docker host. This also works for (rootless) podman. This README.md uses the term docker, but you can read that as both docker and podman (it works for both), unless otherwise specified.

This container will determine the docker host address in the following order

• If set use environment variable DOCKER_HOST. Can be an IP address or a DNS name.
  • This allows you to use this image to forward traffic to arbitrary destinations, not only the docker host.
• Try to resolve host address from DNS names.
  • docker hostname host.docker.internal
  • podman hostname host.containers.internal
• Defaults to default gateway (ip -4 route show default)

By default all ports (1-65535) are forwarded to docker host.

• You may restrict ports by setting environment variable PORTS to a space and/or comma separated list of ports and/or port ranges e.g
  • docker run -e PORTS='443, 8000-9000' ....
• You may also configure port mapping e.g. 443:8443, 8000-9000:5000-6000 (CONTAINER_PORT:HOST_PORT).

These examples will send messages from docker container to docker host with netcat

Start netcat server TCP on port 2323 to receive and display messages

nc -lk 2323

Start netcat server UDP on port 5353 to receive and display messages

nc -lk 5353 -u

Run the dockerhost container.

docker run \
  --name 'docker-host' \
  --cap-add=NET_ADMIN --cap-add=NET_RAW \
  --restart on-failure \
  -d qoomon/docker-host

Run your application container and link the dockerhost container. The dockerhost will be reachable through the domain/link dockerhost of the dockerhost container

docker run --rm \
  --link 'docker-host' \
  -it alpine nc 'docker-host' 2323 -v

docker run --rm \
  --link 'docker-host' \
  -it alpine nc 'docker-host' 5353 -u -v

Create the dockerhost network.

network_name="Network-$RANDOM"
docker network create "$network_name"

Run the dockerhost container within the dockerhost network.

docker run --name "${network_name}-docker-host" \
  --cap-add=NET_ADMIN --cap-add=NET_RAW \
  --restart on-failure \
  --net=${network_name} --network-alias 'docker-host' \
  qoomon/docker-host

Run your application container within the dockerhost network. The dockerhost will be reachable through the domain/link docker-host of the dockerhost container

docker run --rm \
  --link 'docker-host' \
  -it alpine nc 'docker-host' 2323 -v

docker run --rm \
  --link 'docker-host' \
  -it alpine nc 'docker-host' 5353 -u -v

version: '2'

services:
    docker-host:
        image: qoomon/docker-host
        cap_add: [ 'NET_ADMIN', 'NET_RAW' ]
        mem_limit: 8M
        restart: on-failure
    tcp_message_emitter:
        depends_on: [ docker-host ]
        image: alpine
        command: [ "sh", "-c", "while :; do date; sleep 1; done | nc 'docker-host' 2323 -v"]
    udp_message_emitter:
        depends_on: [ docker-host ]
        image: alpine
        command: [ "sh", "-c", "while :; do date; sleep 1; done | nc 'docker-host' 5353 -u -v"]

• https://medium.com/@sam_ngu/connecting-to-docker-host-mysql-from-docker-container-linux-ubuntu-766e526542fd