Function Compute:MQTT triggers

Background information

When you create a trigger in the Function Compute console, Function Compute automatically creates an event stream resource in EventBridge based on the trigger configuration.

After the trigger is created, you can view its details in the Function Compute console. You can also view the automatically created resources in the EventBridge console. When a message arrives in Message Queue for MQTT, the trigger invokes the function. Depending on your batching configuration, one or more message events are pushed to the function in a batch for processing.

Limits

• The Message Queue for MQTT instance and the Function Compute function must be in the same region.

• If you reach the maximum number of event streams, you cannot create more MQTT triggers. For more information about event stream limits, see Limits.

Step 1: Create an MQTT trigger

1. Log on to the Function Compute console. In the left-side navigation pane, click Functions.

2. In the top navigation bar, select a region. On the Functions page, click the function that you want to manage.

3. On the function details page, click the Trigger tab and then click Create Trigger.

4. In the Create Trigger panel, enter the required information and click OK.

   Parameter	Actions	Example
   Trigger Type	Select ApsaraMQ for MQTT.	Message Queue for MQTT
   Name	Enter a custom name for the trigger.	mqtt-trigger
   Version or Alias	The default value is LATEST. If you need to create a trigger for a different version or alias, switch to that version or alias in the upper-right corner of the function details page. For more information, see Manage versions and Manage aliases.	LATEST
   ApsaraMQ for MQTT Instance	Select an existing MQTT instance.	mqtt-xxx
   MQTT topic	Select an existing MQTT topic.	testTopic
   Invocation Method	Select the function's invocation method. Valid values: Sync Invocation: This is the default method. When an event triggers the function, Function Compute waits for the invocation to complete before returning the result. For more information, see synchronous invocations. Async Invocation: This method is suitable for functions with long execution times. When an event triggers the function, Function Compute returns a response immediately. The service ensures that the function is executed at least once, but the execution result is not returned in the response. For more information, see asynchronous invocation.	Synchronous Invocation
   Trigger State	Specifies whether to enable the trigger immediately after creation. By default, this option is selected.	Enable Trigger

   For information about advanced settings such as push configuration, retry policies, and dead-letter queues, see Advanced features of triggers.

   After the trigger is created, it appears on the Triggers tab. To modify or delete the trigger, see Manage triggers.

Step 2: Configure function input parameters

An MQTT event source is passed to a function as an input parameter in the form of an event. You can manually pass an event to the function to simulate an event trigger.

Step 3: Write and test the function code

After you create the trigger, you can write and test your function code to verify that it works correctly. In a production environment, the trigger automatically invokes the function when a message is received by Message Queue for MQTT.

1. On the function details page, go to the Code tab. In the code editor, write your code and click Deploy.

   The following sample code is written in Node.js.

   'use strict';
   /*
   To enable the initializer feature
   please implement the initializer function as below:
   exports.initializer = (context, callback) => {
     console.log('initializing');
     callback(null, '');
   };
   */
   exports.handler = (event, context, callback) => {
     console.log("event: %s", event);
     // Parse the event parameters and process the event. 
     callback(null, 'return result');
   }

2. Click Test Function.

More information

To modify or delete an existing trigger, see Manage triggers.