Docker image to forward TCP and UDP traffic to the docker host.

This container will determine docker host address in the following order

• Use ip from environment variable DOCKER_HOST if set
  • This allows you to use this image to forward traffic to arbitrary destinations, not only the docker host.
• Try to resolve host.docker.internal (getent ahostsv4 host.docker.internal)
• Defaults to default gateway (ip -4 route show default)

⚠️ On Linux systems

• You have to bind your host applications to bridge network gateway in addition to localhost(127.0.0.1).

  Use following docker command to get the bridge network gateway IP address

  docker network inspect bridge --format='{{( index .IPAM.Config 0).Gateway}}'

• You might need to configure your firewall of the host system to allow the docker-host container to communicate with the host on your relevant port, see #21.

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 2323 -lk

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

nc 5353 -lk -u -w0

Run the dockerhost container.

docker run --rm \
  --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"]