Generic MQTT-TCP Last Will and Testament Configuration

4 min

You can use the MQTT Generic connector to send messages to the MQTT broker, which includes a notification to other clients that are connected to the broker when this client disconnects.

When a client connects to the MQTT broker, it creates a connect packet that is predefined and sent to the MQTT broker.

You can define the message to notify you if the client disconnects.

There are four properties that you can set for the Last Will and Testament.

LWT Topic: This is the topic that is used by the MQTT broker to send if the client disconnects.
LWT Payload: This is the payload message that is sent if the client disconnects.
QoS: This is the quality of service level (0, 1, or 2).
Retain: This indicates if the message should be retained (true or false).

The MQTT broker sends this message in the following scenarios:

If the client fails to communicate within the defined Keep Alive period
If the client does not send a disconnect packet before it closes the network connection
The broker closes the network connection due to a protocol error by the client

This example uses MQTT Integration and Flows.

Step 1: Add Generic MQTT Connector

Follow the steps to Add a Connector and select the MQTT - Generic provider.

Configure the following parameters.

Name: A recognizable name to identify the connector.
Hostname: Enter the server address.
Port: Confirm that the default value 1883 is entered.
Client ID: Enter the client ID.
Username (Optional)
Password (Optional)
QoS: The Quality of Service (QoS) level is an agreement between the sender of a message and the receiver of a message that defines the guarantee of delivery for a specific message.
Parallel Publish Count: The number of messages being published simultaneously. Once the defined limit has been reached, subsequent messages are silently dropped. The default value is 100.
Integration Topic: Enter testTopic.
LWT topic: Enter lwtTopicName.
LWT payload: Enter Some LWT Payload.
LWT payload type: The payload type for MQTT's Last Will and Testament feature. The options are string and base64.
LWT QoS: The Quality of Service value for MQTT's Last Will and Testament feature.
LWT retained: Select this check box to retain the value for MQTT's Last Will and Testament feature.
Throttling limit: The maximum number of messages per second to be processed. The default value is zero, which means that there is no limit.
Persistent storage: When enabled, this will cause messages to undergo a store-and-forward procedure. Messages will be stored within Belden Horizon Data Operations when cloud providers are online.

Step 2: Verify Connection in Flows Manager

You can verify the connection is successfully set up by creating a flow in Belden Horizon Data Operations.

To create a flow:

In Belden Horizon Data Operations, navigate to Flows Manager.
Click Add Flow.
Enter MQTT LWT in the Name field and click Create Flow.
Click the Start icon next to the MQTT LWT flow.
Click the Go To Flow Definition icon.
The Flow canvas opens in a new browser tab.
Go To Flow Definition icon
From the node palette, drag the MQTT In node (network section) to the canvas.
MQTT In node
Double-click the MQTT In node. The Edit MQTT In Node dialog box appears.
Click the Edit icon next to the Server field. The Add new mqtt-broker config node dialog box appears.
Edit server icon
In the Name field, enter the name of the broker.
From the Connection tab, configure the following parameters.
- Server: Enter the server address.
- Port: Enter 1883.
- Client ID: Enter the client ID.
- Keep Alive: Enter 60.
Click Add.
From the Edit MQTT In Node dialog box, enter lwtTopicName in the Topic field.
Click Done.
From the Node palette, drag the Debug Node to the canvas and connect the two nodes.
Drag the Sidebar beneath the flow up and click the Debug icon. Verify that messages are displaying.
Debug node messages