MNS queue triggers - Function Compute - Alibaba Cloud Documentation Center

After Message Service (MNS) is integrated with Function Compute as an event source by using EventBridge, you can use MNS queue triggers to trigger the execution of the associated functions and then use the triggered functions to perform custom operations on the messages that are published to MNS. This topic describes how to create an MNS queue trigger, configure the input parameters of the associated function, write function code, and test the function in the Function Compute console.

Overview

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

After the trigger is created, you can view the information about the trigger in the Function Compute console. You can also view the information about the created resources in the EventBridge console. When a message is enqueued in the source MNS queue, the associated function in Function Compute is triggered. During function execution, message events are pushed to the function for processing separately or in batches based on your batch configuration. MNS queue triggers are suitable for scenarios in which end-to-end streaming data is processed.

Usage notes

The MNS queue that is used as the trigger source must reside in the same region as the Function Compute function.
If the number of created event streams exceeds the upper limit, you can no longer create MNS queue triggers.

For information about the limits on the number of resources that are used to create a trigger in one region by using a single Alibaba Cloud account, see Limits.

Before you start

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

Step 1: Create a trigger

Log on to the Function Compute console. In the left-side navigation pane, click Functions.
In the top navigation bar, select a region. On the Functions page, click the function that you want to manage.
On the function details page, click the Configurations tab. In the left-side navigation pane, click Triggers. Then, click Create Trigger.

In the Create Trigger panel, follow the on-screen instructions to configure the parameters and click OK.

The following table describes the basic parameters.

Parameter	Description	Example
Trigger Type	Select MNS Triggered by Queue.	MNS
Name	Enter a custom trigger name.	mns-trigger
Version or Alias	Default value: LATEST. If you want to create a trigger for another version or alias, go back to the Function Details page and switch to the specified version or alias in the upper-right corner. For more information about versions and aliases, see Manage versions and Manage aliases.	LATEST
Queue Name	Select the MNS queue that you created.	MyQueue
Invocation Method	Select a method to invoke the function. Valid values: Sync Invocation: This method is suitable for sequential invocations. When an event or a batch of events triggers the function, Function Compute runs the function and waits for a response before the function processes the next event or batch of events. The maximum payload of a synchronous invocation request is 32 MB. For more information, see Synchronous invocation. Async Invocation: This method allows you to quickly consume events. When an event or a batch of events triggers the function, Function Compute immediately returns a response and continue processing the next event or batch of events. During this process, the function is executed in asynchronous mode. The maximum payload of an asynchronous invocation request is 128 KB. 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. This value indicates that the trigger is enabled immediately after it is created.	N/A

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

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

Step 2: Configure the input parameters of the function

A source event in MNS is passed to the associated function as an input parameter in the form of event. You can manually pass event to the function to simulate event triggering and test whether the function code is correct.

On the Code tab of the function details page, click the icon next Test Function and select Configure Test Parameters from the drop-down list.

In the Configure Test Parameters panel, click the Create New Test Event or Modify Existing Test Event tab, enter the event name and event content, and then click OK.

Sample code of event:

[
    {
    "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":"164901546557****",
    "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"
    }
    },
    {
    "id":"d2g71017-6f65-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":"164901546557****",
    "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 contained in data. For information about parameters that are defined 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.

Step 3: Write function code 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 events that are generated by MNS are delivered to Function Compute by using EventBridge, the trigger automatically triggers the function.

On the Code tab of the Function Details page, write code in the code editor and click Deploy.

The following sample code provides an example on how to write function code 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 parameter and process the event. 
  callback(null, 'return result');
}

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

Additional information

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