Function Compute:ApsaraMQ for MQTT triggers

Background information

After you submit a request to create a trigger in the Function Compute console, Function Compute automatically creates an event stream resource in EventBridge based on the trigger configurations.

After the trigger is created, you can view information about the trigger in the Function Compute console. You can also view information about the created resources in the EventBridge console. When a message is enqueued in ApsaraMQ for MQTT, the execution of a function in Function Compute is triggered. One or more message events are pushed to the function in batches based on your batch configurations.

Limits

• The ApsaraMQ for MQTT instance that is used as the trigger source must be in the same region as the function in Function Compute.

• If the number of event streams exceeds the upper limit, the ApsaraMQ for MQTT triggers can no longer be created. For the upper limit of event streams, see Limits.

Step 1: Create an ApsaraMQ for MQTT trigger

1. Log on to the Function Compute console. In the left-side navigation pane, click Services & Functions.
2. In the top navigation bar, select a region. On the Services page, click the desired service.
3. On the Functions page, click the name of the desired function.

4. On the function details page, click the Triggers tab, select a version or alias from the Version or Alias drop-down list, and then click Create Trigger.

5. In the Create Trigger panel, configure the parameters and click OK.

   Parameter	Description	Example
   Trigger Type	Select ApsaraMQ for MQTT.	ApsaraMQ for MQTT
   Name	Enter a trigger name.	mqtt-trigger
   Version or Alias	The default value is LATEST. If you want to create a trigger for another version or alias, switch to the trigger of the version or alias in the upper-right corner of the function details page. For more information about versions and aliases, see Manage versions and Manage aliases.	LATEST
   ApsaraMQ for MQTT Instance	Select an ApsaraMQ for MQTT instance.	mqtt-xxx
   MQTT Topic	Select an ApsaraMQ for MQTT topic.	testTopic
   Invocation Method	Select the method to invoke the function. Options: Sync Invocation: After an event triggers the function, Function Compute waits for the function invocation to complete before it returns responses. For more information, see Synchronous invocations. Async Invocation: After an event triggers the execution of a function, Function Compute immediately returns a response and ensures that the function is successfully executed at least once. However, the detailed execution result is not returned. This invocation method is suitable for functions that have higher scheduling latency. For more information, see Overview.	Sync Invocation
   Trigger State	Specify whether to enable the trigger immediately after it is created. By default, Enable Trigger is selected and the trigger is immediately enabled after it is created.	Enable Trigger

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

   The trigger is displayed in the Triggers tab after it is created. To modify or delete a created trigger, see Manage triggers.

Step 2: Configure the input parameters of the function

An ApsaraMQ for MQTT event source is passed to the function in the form of event, which acts as the input parameter. You can manually pass event to the function to trigger the function.

Step 3: Write and test the function

After you create the trigger, you can write function code and test the function to verify whether the code is correct. When ApsaraMQ for MQTT receives a message, the trigger automatically triggers the function.

1. On the function details page, click the Code tab, enter function code in the code editor, and then click Deploy.

   In this topic, sample code in a Node.js runtime is used as an example.

   '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 the Code tab and click Test Function.
   After the function is executed, you can view the result on the Code tab.

Additional information

In addition to the Function Compute console, you can configure triggers by using the following methods:

• Use Serverless Devs to configure triggers. For more information, see Create a trigger.

• Use SDKs to configure triggers. For more information, see SDKs.

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