Plugins

Plugins are containers the Supervisor runs for the system itself, not for the user. They provide services that Core and apps share, like DNS and audio. Users don't install or remove them, and the Supervisor updates them automatically.

On the Supervisor side, every plugin is a class in supervisor/plugins/, based on PluginBase. It handles installing, starting, updating, and repairing the container, and a watchdog restarts it when it stops. Each plugin's image is ghcr.io/home-assistant/<arch>-hassio-<plugin>, and the versions come from the same version file as everything else.

Plugin	Container	Repository	What it is
DNS	hassio_dns	plugin-dns	CoreDNS, for name resolution in the containers
Audio	hassio_audio	plugin-audio	PulseAudio, for sound in and out
CLI	hassio_cli	plugin-cli	The ha command line
Multicast	hassio_multicast	plugin-multicast	An mDNS repeater
Observer	hassio_observer	plugin-observer	A status page that works when nothing else does

Every container on the hassio network uses the DNS plugin as its name server. It runs CoreDNS with two plugins of its own:

• mdns resolves .local names, by asking systemd-resolved on the host over D-Bus.
• fallback retries failed lookups against Cloudflare's DNS over TLS, when the fallback is on.

The Supervisor writes a hosts file with the names of the containers, like supervisor and homeassistant, so they can reach each other by name. Other lookups go to the DNS servers of the host, or the ones the user set with ha dns options. The configuration template is rootfs/usr/share/tempio/corefile in the plugin repository.

The audio plugin runs PulseAudio on top of ALSA, so Core and apps that need audio share one sound system. Apps get access when their configuration asks for audio. All audio configuration lives in this container, which lets users adjust PulseAudio without touching the host. ha audio shows the devices and sets the defaults.

The CLI plugin is the ha command line, built from the home-assistant/cli repository. On Home Assistant OS it is the login shell on the console: the host runs it when you log in, see debug the host. The plugin repository only packages the CLI. Changes to the commands themselves go to the cli repository.

The multicast plugin runs mdns-repeater on the host network. It repeats mDNS traffic between the host network and the hassio network, so discovery works across that boundary. It can be turned off through the Supervisor API.

The observer is a small web server, written in Go, on port 4357 of the host. It shows whether the Supervisor is running and healthy, and its logs. It runs separately from the Supervisor on purpose: when the Supervisor or Core is down, the observer is how users still see what is going on.

Each plugin repository builds a container image, mostly from a Dockerfile and a rootfs/ folder, and several have a development container. Most plugins have ha <plugin> commands to show their logs, restart them, or update them, like ha dns logs or ha audio restart.

To try your own build on a device, build the image for the device's architecture, and tag it with the image name and version the plugin runs now (docker ps on the host shows it). Then restart the plugin. The approach is the same as testing the Supervisor on a real system. Keep in mind that the Supervisor updates plugins automatically, which replaces your build when a new version comes out.