homeassistant

Your comment isn't entirely accurate.

in an overwhelming amount of cases, that host networking will be a "here's a device-local subnet your containers can join to", so no, a Docker container won't by default "get it's own IP address"

With the default NAT network, it gets its own IP in the 172.16.x.x range that Docker decides to use. That IP is accessible from the Docker host. It doesn't matter that it's not on your LAN - it's still a dedicated IP. Port forwarding (or a reverse proxy) to it is a separate thing, and you can map a different port if you want to.

Plenty of Docker containers use the same port (often 80, 3000 or 8000), and the reason you can use multiple of those containers concurrently is because each one is on a separate IP.

The default NAT network isn't commonly used for Home Assistant, though. It usually has a direct network connection to the LAN, since plenty of smart home devices rely on broadcasts for discovery.

Also claiming that "nothing else will use port 80" is a gross over-simplification.

It's true for both the Home Assistant Docker container and for HAOS. In both cases, there's no other web servers running in the container/VM. For the Docker container:

• If you're using the default Docker NAT network, the port you use to expose it to other devices is completely unrelated to the port used in the container. When you expose a Docker port, you specify the host port and container port separately.

  • Sometimes the port isn't exposed to the LAN at all, for example if you're using a reverse proxy. In that case, you usually use the docker container name as the upstream in your Nginx config or whatever, like proxy_pass http://hass/

• If you bridge the Docker container to the LAN, it has its own IP on the LAN and no other web servers will be running on that IP.

The actual reason that Docker containers don't use port 80 by default is so they're able to run in rootless mode without any extra capability grants. I don't think Home Assistant supports rootless mode though.