MQTT

gatOS can run an embedded MQTT broker at 127.0.0.1:1883 by default. The Alpine guest reaches it at $GATOS_MQTT, normally sim:<port>. It is handy when your program wants a pub/sub feed instead of polling an HTTP endpoint.

The broker publishes aggregate snapshots and live events, plus an optional field mirror under gatos/sim/<path>. Send the generic JSON command envelope to gatos/command, or raw control text to gatos/sim/<path>/set where the field mirror is enabled.

gatos/snapshot
gatos/events
gatos/sim/vessels/active/altitude/radar
gatos/command

The world feed can be paced with mqtt_publish_hz; field topics have their own cadence. Retained snapshots are useful for a subscriber that arrives after launch, while event topics are for things that happened along the way.

Exposing the broker

Set mqtt_bind_host to a specific host-interface IP or 0.0.0.0 for all IPv4 interfaces when networked mission control needs direct access. The embedded broker has no authentication, so every reachable client can subscribe and publish commands.

The MQTT reference has the exact topic families, retained behavior, command payloads, and cadence rules.