MNS queue triggers

Overview

Usage notes

• In EventBridge, the number of custom event buses in the same region cannot exceed 10, and the number of event rules that are created on each custom bus cannot exceed 10. If the limits are reached, you cannot create EventBridge triggers.
• The created MNS queue and the Function Compute functions must be in the same region.
• You cannot create MNS queue triggers by using Serverless Devs or SDKs.

Prerequisites

• EventBridge
  • Activate EventBridge and grant permissions to a RAM user
• Function Compute
  • Create a Service
  • Create a function
• MNS
  • Activate MNS and authorize RAM users to access MNS
  • Create a queue

Step 1: Create a trigger

1. Log on to the Function Compute console.
2. In the left-side navigation pane, click Services and Functions.
3. In the top navigation bar, select the region where the service resides.
4. On the Services page, find the desired service and click Functions in the Actions column.
5. On the Functions page, click the function that you want to manage.
   
6. On the function details page, click the Triggers tab, select the version or alias from the Version or Alias drop-down list, and then click Create Trigger.
7. In the Create Trigger panel, specify related parameters. After you specify the parameters, click OK.
   

   Parameter	Description	Example
   Trigger Type	Select MNS from the drop-down list.	MNS
   Name	Enter a custom trigger name	mns-trigger
   Version or Alias	The default value is LATEST. If you want to create a trigger of another version or alias, switch to the trigger of the specified version or alias in the upper-right corner of the function details page. For more information about versions and aliases of a service, see Manage versions and Manage aliases.	LATEST
   Queue Name	Select a MNS queue.	MyQueue
   Invocation Method	The function invocation method. Valid values: Synchronous Invocation: After an event triggers the execution of a function, Function Compute returns the result when the execution is complete. This is the default value. For more information, see Synchronous invocations. Asynchronous 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 relatively higher scheduling latency. For more information, see Asynchronous calls.	Synchronous Invocation

   After the trigger is created, it is displayed on the Triggers tab.

Step 2: Write a function

After you create an MNS queue trigger, you can write the function code.

'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);
  handle_event(event);
  callback(null, 'return result');
}

Step 3: Test the function

After you write the function, you must debug the function to verify whether the code is correct. When the events that are generated by the MNS custom event sources are delivered to Function Compute by using EventBridge, function execution is automatically triggered.

An MNS event is passed to the function as an input parameter. You can manually pass an event to the function to trigger the function and test whether the code of the function is correct.

1. On the function details page, click the Code tab and click the icon. From the drop-down list that appears, select Configure Test Parameters.
2. In the Configure Test Parameters panel, click the Create New Test Event or Modify Existing Test Event tab, and specify Event Name and the event content. After you specify the parameters, click OK.

   The event parameter is an input parameter of Function Compute. The following code shows the format of the event parameter:

   {
       "id":"c2g71017-6f65-fhcf-a814-a396fc8d****",
       "source":"MNS-Function-mnstrigger",
       "specversion":"1.0",
       "type":"mns:Queue:SendMessage",
       "datacontenttype":"application/json; charset=utf-8",
       "subject":"acs:mns:cn-hangzhou:164901546557****:queues/zeus",
       "time":"2021-04-08T06:28:17.093Z",
       "aliyunaccountid":"1649015465574023",
       "aliyunpublishtime":"2021-10-15T07:06:34.028Z",
       "aliyunoriginalaccountid":"164901546557****",
       "aliyuneventbusname":"MNS-Function-mnstrigger",
       "aliyunregionid":"cn-chengdu",
       "aliyunpublishaddr":"42.120.XX.XX",
       "data":{
           "requestId":"606EA3074344430D4C81****",
           "messageId":"C6DB60D1574661357FA227277445****",
           "messageBody":"TEST"
       }
   }

   The following table describes the parameters in the data field. For more information about the parameter definition in the CloudEvents specification, see Overview.

   Parameter	Type	Example	Description
   requestId	String	606EA3074344430D4C81****	The ID of the request. The ID of each request is unique.
   messageId	String	C6DB60D1574661357FA227277445****	The ID of the message. The ID of each message is unique.
   messageBody	String	TEST	The content of the message.

3. On the function details page, click the Code tab and click Test Function.

Verify results

After the function is executed, a message appears on the Code tab to indicate that the execution is successful.

References

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