如何在CloudFormation栈中将Step Function的ARN传递给其他函数

问题说明 #

在CloudFormation栈中创建了Step Function，需要让栈内的另一个函数在部署完成后调用它，计划将Step Function的ARN作为环境变量传递给目标函数，但遇到了循环依赖问题，当前代码中全局函数配置里的STEP_FUNCTION错误引用了Research函数的ARN，而非Step Function本身的ARN。

解决方案 #

1. 修正ARN引用目标：将环境变量STEP_FUNCTION指向Step Function状态机的ARN，而非Research函数的ARN
2. 明确依赖关系：调整目标函数的DependsOn属性，确保它在Step Function部署完成后再创建，避免循环依赖
3. 修正Step Function定义中的函数ARN引用：原代码中状态机定义里的${VideoResearch.Arn}应为${Research.Arn}（资源名为Research）

修改后的CloudFormation代码示例 #

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
    reports stack

Globals:
    Function:
        Timeout: 120
        MemorySize: 2048
        Runtime: python3.9
        Environment:
            Variables:
                # 修正为引用Step Function状态机的ARN
                STEP_FUNCTION: !Ref StepFunctionToHandleVideosResearch

Parameters:
    ProjectName:
        Description: Name of the Project
        Type: String
        Default: Project

Resources:
    MyApi:
      Type: AWS::Serverless::Api
      Properties:
        StageName: Prod
        TracingEnabled: true
        Cors: 
          AllowMethods: "'DELETE,GET,HEAD,OPTIONS,POST,PUT'"
          AllowHeaders: "'Content-Type,X-Amz-Date,Authorization,X-Api-Key,X-Amz-Security-Token'"
          AllowOrigin: "'*'"
        
    List:
        # 修正依赖为Step Function状态机，确保先创建Step Function再创建该函数
        DependsOn: StepFunctionToHandleVideosResearch
        Type: AWS::Serverless::Function 
        Properties:
            CodeUri: functions/
            Handler: get.get         
            Events:
                List:
                    Type: Api 
                    Properties:
                        RestApiId: !Ref MyApi
                        Path: /reports
                        Method: GET
            Policies:
                (...)

    ################ STEP FUNCTION ################
    Research:
      Type: AWS::Serverless::Function 
      Properties:
        CodeUri: functions/
        Handler: runResearch.research
        Policies:
            (...)
  
    StepFunctionToHandleResearchRole:
      Type: "AWS::IAM::Role"
      Properties:
        AssumeRolePolicyDocument:
          Version: "2012-10-17"
          Statement:
            - Effect: "Allow"
              Principal:
                Service:
                  - !Sub states.${AWS::Region}.amazonaws.com
              Action: "sts:AssumeRole"
        Path: "/"
        Policies:
          (...)

    StepFunctionToHandleVideosResearch:
      Type: "AWS::StepFunctions::StateMachine"
      Properties:
        DefinitionString: !Sub |
              {
                "StartAt": "Research",
                "States": {
                  "Research": {
                    "Type": "Task",
                    # 修正为引用Research函数的ARN
                    "Resource": "${Research.Arn}", 
                    "End": true
                  }
                }
              }
        RoleArn: !GetAtt [ StepFunctionToHandleResearchRole, Arn ]

Outputs:
    # 可选：输出Step Function的ARN方便后续查看
    StepFunctionARN:
        Value: !Ref StepFunctionToHandleVideosResearch
        Description: ARN of the Research Step Function

函数代码获取环境变量 #

在Python函数中，通过以下代码即可正确获取Step Function的ARN：

import os

stepFunctionARN = os.environ['STEP_FUNCTION']

关键说明 #

• !Ref StepFunctionToHandleVideosResearch可以直接获取状态机的ARN，和!GetAtt [StepFunctionToHandleVideosResearch, Arn]效果一致
• 通过DependsOn: StepFunctionToHandleVideosResearch确保List函数在Step Function完全创建后再部署，避免因ARN未生成导致的部署错误
• 原代码中的循环依赖大概率是因为错误地让List函数依赖Research函数，同时Step Function也依赖Research函数，而List函数又需要Step Function的ARN，调整依赖关系后即可解决

内容的提问来源于stack exchange，提问作者Tibo