Custom Resource Lambda should run on Create but instead runs on first Update-CodePudding

As per the AWS documentation here (See: RequestType) a custom Lambda function can be triggered by CloudFormation operations of the types: create-stack, update-stack, or delete-stack operations.

My lambda is configured to only do its task on create-stack, but when I added this Custom Resource and Lambda to my (pre-existing) CloudFormation stack and updated it, the lambda ran as if the stack was created, even though it was updated.
Should it not run only for the first create? Why would it work for the first update?

Note: It did not run for subsequent updates

Relevant Code Snippets

CloudFormation Resources:

LambdaUpdateNodeStatusFunction:
    Type: AWS::Serverless::Function
    Properties:
      FunctionName: !Ref LambdaUpdateNodeStatusFunctionName
      CodeUri: ../../../bin/handlers/espnode/lambdaupdatenodesstatus_c
      Handler: lambdaupdatenodesstatus
      Role: !GetAtt LambdaUpdateNodeStatusExecutionRole.Arn
      MemorySize: 512 #MB
      Timeout: 900

  LambdaUpdateNodeStatusFunctionLog:
    Type: AWS::Logs::LogGroup
    Properties:
      LogGroupName: !Join ["", ["/aws/lambda/", !Ref LambdaUpdateNodeStatusFunctionName]]
  
  LambdaUpdateNodeStatusCustomResource:
    Type: Custom::LambdaUpdateNodeStatusCustomResource
    Properties:
      ServiceToken: !GetAtt LambdaUpdateNodeStatusFunction.Arn
      Version: !Ref BuildVersion

Lambda Code:


type CustomLambdaRequest struct {
    RequestType        string `json:"RequestType"`
    ResponseURL        string `json:"ResponseURL"`
    StackId            string `json:"StackId"`
    RequestId          string `json:"RequestId"`
    ResourceType       string `json:"ResourceType"`
    LogicalResourceId  string `json:"LogicalResourceId"`
    PhysicalResourceId string `json:"PhysicalResourceId"`
}

func Handler(customLambdaRequest CustomLambdaRequest) {

    if customLambdaRequest.RequestType == "Create" {
        // Do some processing here
    } else {
        // Do Nothing here
    }
}

CodePudding user response：

The Lambda-backed custom resources are triggered, as you mentioned, in the create-stack, update-stack, and delete-stack operations.

But they are triggered for each custom resource that is part of your template.

That means that when you add a new Custom:: resource to your template, it will call the lambda with RequestType == Create and save the LogicalResourceId in the cloud formation state. Later when you update the stack it will trigger the function with the update request type and so on.