During my attempts to configure the OH3 MQTT system broker connection, I noticed a possible bug.
I am able to make the first configuration and save it under an arbitrary “Connection name”:
The operation is logged in /var/log/openhab/openhab.log:
2021-02-22 14:55:06.507 [INFO ] [g.discovery.internal.PersistentInbox] - Added new thing 'mqtt:systemBroker:mqtt-system-broker' to inbox. 2021-02-22 14:55:06.514 [INFO ] [.transport.mqtt.MqttBrokerConnection] - Starting MQTT broker connection to '10.0.0.3' with clientid mqtt2-system-broker
But if I want to make any changes AFTER this step, I get the following warning and the changes are NOT saved:
2021-02-22 14:56:58.249 [WARN ] [.MqttBrokerConnectionServiceInstance] - Ignore existing broker connection configuration for: mqtt-system-broker
The only way to overcome this is to change the Connection name and then Save the settings again.
If I try to re-use any Connection name previously used, the settings cannot be saved (“ignore existing broker” warning), so I believe these connections appear as “ghost” entries somewhere in the OH3 settings database.