aws-lambda - Lambda 支持的自定义资源 cf 模板返回 'CREATE_FAILED'

Question

下面的 lambda 函数是将 SNS 主题关联到现有目录，然后是自定义资源来调用 lambda 函数本身。我看到 lambda 创建成功，“Register_event_topic”也完成。然而，堆栈在一段时间后失败，主要是因为“自定义资源未能在预期时间内稳定下来”；如何保证堆栈不会出错？

AWSTemplateFormatVersion: '2010-09-09'
    #creating lambda function to register_event_topic
    Description: Lambda function to register event topic with existing directory ID
    Parameters:
      RoleName:
        Type: String
        Description: "IAM Role used for Lambda execution"
        Default: "arn:aws:iam::<<Accountnumber>>:role/LambdaExecutionRole"
      EnvVariable:
        Type: String
        Description: "The Environment variable set for the lambda func"
        Default: "ESdirsvcSNS"
    Resources:
      REGISTEREVENTTOPIC:
        Type: 'AWS::Lambda::Function'
        Properties:
          FunctionName: dirsvc_snstopic_lambda
          Handler: index.lambda_handler
          Runtime: python3.6
          Description: Lambda func code to assoc dirID with created SNS topic
          Code:
            ZipFile: |
              import boto3
              import os
              import logging
              dsclient = boto3.client('ds')
              def lambda_handler(event, context):
                response = dsclient.describe_directories()
                directoryList = []
                print(response)
                for directoryList in response['DirectoryDescriptions']:
                    listTopics = dsclient.describe_event_topics(
                      DirectoryId=directoryList['DirectoryId']
                    )
                    eventTopics = listTopics['EventTopics']
                    topiclength = len(eventTopics)
                    if topiclength == 0:
                      response = dsclient.register_event_topic(
                          DirectoryId=directoryList['DirectoryId'],
                          TopicName= (os.environ['MONITORING_TOPIC_NAME'])
                      )  
                    print(listTopics)
          Timeout: 60
          Environment:
            Variables:
              MONITORING_TOPIC_NAME: !Ref EnvVariable
          Role: !Ref RoleName

      InvokeLambda:
        Type: Custom::InvokeLambda
        Properties:
          ServiceToken: !GetAtt REGISTEREVENTTOPIC.Arn
          ReservedConcurrentExecutions: 1

Answer 1

唉，编写自定义资源并不像您最初想象的那么简单。相反，必须添加特殊代码来将响应发布回 URL。

您可以在以下位置提供的示例 Zip 文件中看到这一点:Walkthrough: Looking Up Amazon Machine Image IDs - AWS CloudFormation

来自Custom Resources - AWS CloudFormation文档:

The custom resource provider processes the AWS CloudFormation request and returns a response of SUCCESS or FAILED to the pre-signed URL. The custom resource provider provides the response in a JSON-formatted file and uploads it to the pre-signed S3 URL.

这是由于 CloudFormation 的异步行为造成的。它并不是简单地调用 Lambda 函数然后等待响应。相反，它会触发 Lambda 函数，并且该函数必须回调并触发 CloudFormation 中的下一步。