A way to a container in a guest VM connect to a host's container?

[nicystalker]

Hi, I was wondering if it is possible to connect to a container, say a Postgres container, that is running on a host machine, MacOS in my case, from another container running a guest VM; again, in my case is an Arch Linux instance, configured imported to UTM.

The UTM Arch Linux instance is configured to share the host's (MacOS) network. For example, the host would be "192.168.0.X" and the guest "192.168.64.Y".

Both host and guest have podman installed, and are used in rootless mode (the default).

The host container is started issuing:

me@mylaptop ~> podman run  -p 5432:5432 -e POSTGRES_PASSWORD=123 -d postgres
me@mylaptop ~> podman ps
CONTAINER ID  IMAGE                              COMMAND     CREATED         STATUS         PORTS                             NAMES
577b89692c28  docker.io/library/postgres:latest  postgres    30 seconds ago  Up 30 seconds  0.0.0.0:5432->5432/tcp, 5432/tcp  festive_wozniak

Also, it seems that --net host odes not work with port mappings:

me@mylaptop ~> podman run --net host -p 5432:5432 -e POSTGRES_PASSWORD=123 -d postgres
Port mappings have been discarded as one of the Host, Container, Pod, and None network modes are in use
81a64c8b7b2fef8fd01201247514c8dd93b31a54a9b4075103b802008f1b8f06

me@mylaptop ~> podman ps
CONTAINER ID  IMAGE                              COMMAND     CREATED        STATUS        PORTS       NAMES
81a64c8b7b2f  docker.io/library/postgres:latest  postgres    3 seconds ago  Up 3 seconds              heuristic_brown

And I try to connect to this very same container within the guest VM, through another container, like so:

arch@archlinux ~> podman run -it --net host --rm docker.io/postgres:16-alpine psql -h 192.168.0.2 -U postgres
psql: error: connection to server at "192.168.0.2", port 5432 failed: server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.

arch@archlinux ~> podman run -it --network host --rm docker.io/postgres:16-alpine psql -h host.containers.internal -U postgres
psql: error: connection to server at "host.containers.internal" (192.168.64.2), port 5432 failed: Connection refused
        Is the server running on that host and accepting TCP/IP connections?

The message "Is the server running on that host and accepting TCP/IP connections?" gave me the idea to configure port forwarding in UTM, to no avail.

I'm not quite sure what to look for or what am I missing. This tutorial shows what I'm trying to achieve: https://pinter.org/archives/7719

Maybe Caddy can come in handy here?

[Update on --net=host]

Oh, it is expected that the mappings won't work:

WARNING: Published ports are discarded when using host network mode
– https://docs.docker.com/engine/network/drivers/host/

[nicystalker]

Not sure if changes related to version 5.3 afected this, but now I'm able to connect.