Greengrass Mqtt5 SESSION_TAKEN_OVER

Question

I noticed this happening today on my testing GGv2 device. From the greengrass.log file I see the following errors popping up about every two minutes. Here they are grep'd out so the timing can be seen:

```
./greengrass_2023_12_21_19_0.log:2023-12-21T20:48:25.466Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
./greengrass_2023_12_21_19_0.log:2023-12-21T20:50:26.353Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
./greengrass_2023_12_21_19_0.log:2023-12-21T20:52:27.607Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
./greengrass_2023_12_21_19_0.log:2023-12-21T20:54:28.515Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
./greengrass_2023_12_21_19_0.log:2023-12-21T20:56:29.535Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
./greengrass_2023_12_21_19_0.log:2023-12-21T20:58:30.561Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
./greengrass_2023_12_21_20_0.log:2023-12-21T21:00:30.822Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
./greengrass_2023_12_21_20_0.log:2023-12-21T21:02:32.069Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
```

I'm not finding much information regarding the "SESSION_TAKEN_OVER" code.

Answer

Hello,

The error could mean that you have multiple MQTT clients running and supplying the same ClientID or you have multiple Greengrass  instances running on the same device.

> The message broker uses the client ID to identify each client. The client ID is passed in from the client to the message broker as part of the MQTT payload. Two clients with the same client ID can't be connected concurrently to the message broker. When a client connects to the message broker using a client ID that another client is using, the new client connection is accepted and the previously connected client is disconnected.

Greengrass Mqtt5 SESSION_TAKEN_OVER

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