I want to connect two Docker containers, defined in a Docker-Compose file to each other (app and db). And one of them (app) should also be connected to the host network.
The containers should be connected to a common user-defined network (appnet or default) to use the embedded DNS capabilities from docker networking.
app needs also to be directly connected to the host network to receive ethernet broadcasts (network layer 2) in the physical network of the docker host.
If I use both directives network_mode: host and networks in compose together, I get the following error.
ERROR: 'network_mode' and 'networks' cannot be combined
So I have to do this with networks only!?
version: "3.3"
services:
app:
build: .
image: app
container_name: app
environment:
- MONGODB_HOST=db
depends_on:
- db
networks:
- appnet
- hostnet
db:
image: mongo:latest
container_name: db
networks:
- appnet
networks:
appnet:
hostnet:
external:
name: host
The foregoing compose file produces a error.
ERROR: for app network-scoped alias is supported only for containers in user defined networks
If I use the network name host in the service without defining it in networks (because it already exists), it says.
ERROR: Service "app" uses an undefined network "host"
How to use the host network, and any other user-defined network (or the default) together in Docker-Compose?
I'm using Docker version 17.11.0-ce-rc3, build 5b4af4f and docker-compose version 1.17.1, build 6d101fb
TL;DR you can't. The host networking turns off the docker network namespace for that container. You can't have it both on and off at the same time.
Instead, connect to your database with a published port, or a unix socket that you can share as a volume. E.g. here's how to publish the port:
version: "3.3"
services:
app:
build: .
image: app
container_name: app
environment:
- MONGODB_HOST=127.0.0.1
db:
image: mongo:latest
container_name: db
ports:
- 127.0.0.1:27017:27017
To use host network, you don't need to define it. Just use "ports" keyword to define, which port(s) from service you want to expose in host network.
Since Docker 18.03+ one can use host.docker.internal to access your host from within your containers. No need to add host network or mix it with the user defined networks.
Source: Docker Tip #65: Get Your Docker Host's IP Address from in a Container
来源：https://stackoverflow.com/questions/47303141/how-to-use-the-host-network-and-any-other-user-defined-network-together-in-dock