Function Compute:Simple Message Queue (formerly MNS) topic triggers

Overview

Simple Message Queue (formerly MNS) is a distributed messaging service that features high scalability, efficiency, reliability, security, and convenience. MNS allows application developers to transfer data and notifications between the distributed components of an application and build a loosely coupled system. In Simple Message Queue (formerly MNS), messages are published to topics. A publisher can call the PublishMessage operation to publish a message to a topic, and a subscriber to the topic receives the message. For more information, see PublishMessage.

Configuring a trigger for an Simple Message Queue (formerly MNS) topic is equivalent to registering a function as a subscriber to the Simple Message Queue (formerly MNS) topic. When a publisher publishes a message to the Simple Message Queue (formerly MNS) topic, the message is passed to the function and used as the event parameter of the function handler to trigger the function. For more information, see Basics.

The following benefits are delivered after Simple Message Queue (formerly MNS) and Function Compute are integrated:

• Allows you to perform advanced processing on a message before you send the message in an email or a text message.

• Does not require you to create services at HTTP endpoints.

• Supports abundant custom operations. For example, you can send a message to Slack or persist a specified message.

Before you start

• Function Compute

  • Create a service

  • Creates a function

• Simple Message Queue (formerly MNS)

  • Create a topic

Usage notes

• The Simple Message Queue (formerly MNS) topic and the Function Compute function to be associated must reside in the same region.

• You must avoid recursive invocations.

  Avoid the following logic when you write code for a function: Topic A triggers Function B, and Function B publishes a new message to Topic A, which then triggers Function B again. This logic results in an infinite loop of function invocations.

Step 1: Create an Simple Message Queue (formerly MNS) topic 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, find the desired service and click Functions in the Actions column.

3. On the Functions page, click the function that you want to modify.

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, specify the parameters and click OK.

   Parameter	Description	Example
   Trigger Type	Select Simple Message Queue (formerly MNS) Triggered by Topic.	Simple Message Queue (formerly MNS) Triggered by Topic
   Name	Enter a trigger name.	trigger-mns
   Version or Alias	The default value is LATEST. If you want to create a trigger for another version or alias, select a 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
   MNS Region	Select the region where the topic resides. The Simple Message Queue (formerly MNS) topic must reside in the same region as the Function Compute function.	China (Chengdu)
   Topic	Select a topic from the list.	Mytopic
   Filter Tag	Specify a tag for message filtering. Function execution is triggered only when a message that contains the specified filtering tag is received.	tag
   Event Format	Select an event format. Valid values: STREAM JSON	JSON
   Retry Policy	Select a retry policy. Valid values: Backoff Retry Exponential Decay Retry For more information about how to select a retry policy, see NotifyStrategy.	Backoff Retry
   Role Name	Select AliyunMNSNotificationRole. Note After you configure the preceding parameters, click OK. If this is the first time you create a trigger of this type, click Authorize Now in the dialog box that appears.	AliyunMNSNotificationRole

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

Step 2: Configure the input parameters of the function

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

2. In the Configure Test Parameters panel, select the Create New Test Event or Modify Existing Test Event tab, configure Event Name and the event content in the code editor, and then click OK.

   Messages that are published on an Simple Message Queue (formerly MNS) topic are processed based on notifyContentFormat, which is the event of the handler function. For more information, see NotifyContentFormat.

   • If you set Event Format to STREAM:

     • The following code shows the format of the event parameter if messages do not contain message attributes:

       Note

       If messages do not contain message attributes, the content of the event parameter is a string in JSON format.

       # The message body. 
       'hello topic'

     • The following code shows the format of the event parameter if messages contain message attributes:

       Note

       The content of the event parameter contains the key-value pairs that are related to message attributes. For more information, see PublishMessage.

          {
               "body": "hello topic",
               "attrs": {
                   "Extend": "{\\"key\\":\\"value\\"}"
               }
           }                    

   • If you set Event Format to JSON:

     • The following code shows the format of the event parameter if messages do not contain message attributes:

           {
               "TopicOwner": "118620210433****",
               "Message": "hello topic",
               "Subscriber": "118620210433****",
               "PublishTime": 1550216480040,
               "SubscriptionName": "test-fc-subscribe",
               "MessageMD5": "BA4BA9B48AC81F0F9C66F6C909C3****",
               "TopicName": "Mytopic",
               "MessageId": "2F5B3C082B923D4EAC694B76D928****"
           }        
                                   

     • The following code shows the format of the event parameter if messages contain message attributes:

       Note

       The content of the event parameter contains the key-value pairs that are related to message attributes. For more information, see PublishMessage.

           {
               "key": "value",
               "TopicOwner": "118620210433****",
               "Message": "hello topic",
               "Subscriber": "118620210433****",
               "PublishTime": 1550216302888,
               "SubscriptionName": "test-fc-subscribe",
               "MessageMD5": "BA4BA9B48AC81F0F9C66F6C909C3****",
               "TopicName": "Mytopic",
               "MessageId": "2F5B3C281B283D4EAC694B742528****"
           }
                                   

   The following table describes the fields in the event parameter.

   Field	Value type	Example	Description
   key	String	value	The key-value pairs that are related to message attributes.
   TopicOwner	String	118620210433****	The ID of the account that subscribed to the topic.
   Message	String	hello topic	The content of the message.
   Subscriber	String	118620210433****	The account ID of the user.
   PublishTime	Int	1550216302888	The time when the message was published.
   SubscriptionName	String	test-fc-subscribe	The name of the subscription.
   MessageMD5	String	BA4BA9B48AC81F0F9C66F6C909C3****	The MD5 hash value of the message body.
   TopicName	String	Mytopic	The name of the MNS topic.
   MessageId	String	2F5B3C281B283D4EAC694B742528****	The message ID.

Step 3: Write function code and test the function

After you create the Simple Message Queue (formerly MNS) topic trigger, you can write function code and test the function to verify whether the code is correct.

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

   In this example, the function code is written in Python. The following sample code can be used as a function template for an Simple Message Queue (formerly MNS) topic trigger.

   import json
   import logging
   
   def handler(event, context):
     logger = logging.getLogger()
     logger.info("mns_topic trigger event = {}".format(event))
     # For example, record an event to Tablestore. 
     return "OK"                     

2. On the Code tab, 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.