Access services running on the host machine inside a Swarm-managed container

[kevinbioj (Kevin)]

Hello,

I’m deploying a simple application that relies on a PostgreSQL and a Redis instance.
These instances are live on the host machine, outside of any container.

My application needs to connect to these services.
However, I can’t find a way to connect to the host machine network from the container…

I tried creating an external network with the overlay driver and the --attachable flag, but nothing.
And I can’t seem to be able to create any other network type due to Swarm restrictions.

I could switch back to a simple Docker Compose, however I really like the way deployment is handled via Swarm… and it would annoy me to return back to something more primitive.

Is there a way to “mount” the host’s localhost into some IP address inside the container?

Thanks.

[rimelek (Ákos Takács)]

I don’t know if the last solution would work the same way with swarm, but I just shared it in another topic minutes ago.

Getting Docker to connect to proxy running on hosts Localhost address

host.docker.internal is only available in Docker Desktop. Using Docker Engine (Docker CE) you can Use the host IP and protect the proxy with firewall rules against external requests. Allow the proxy to listen on any private IP on the host which is available from containers Use socat to implement a similar solution to the host.docker.internal domain in Docker Desktop: Host.docker.internal in production environment - #4 by rimelek

For swarm host network I found this old topic

Use host network for swarm container

Hi, according to this, starting on Docker 17.06 I can use a host network for a swarm service. I tried adding network_mode to a service in my config file but it gets ignored. Ignoring unsupported options: network_mode Isn’t that the correct option? My service is defined along these lines: version: ‘3.4’ services: coturn: image: boldt/coturn hostname: xxx network_mode: host … deploy: replicas: 1 restart_policy: condition: on-failure delay: 5s max_attempts: 3 window: 120s

I don’t know what your expectation was by using overlay networks. Maybe I get something wrong, but you either use the host network mode in containers or make a service listen on an IP which is available from containers.

[bluepuma77]

Your host has a real IP (not localhost / 127.0.0.1), which your local services are listening on. You can always use that IP to connect to host from inside a container.

[meyay (Metin Y.)]

And if the service on the host binds to 0.0.0.0, you should be able to reach it on the docker0 interface ip, which defaults to 172.17.0.1.