Example S3 -> SNS -> Lambda SAM template.

template.yaml

AWSTemplateFormatVersion: 2010-09-09
Transform: AWS::Serverless-2016-10-31
Resources:
  Bucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: !Sub my-bucket-${AWS::AccountId}
      NotificationConfiguration:
        TopicConfigurations:
          - Event: s3:ObjectCreated:*
            Topic: !Ref S3ObjectChangeEvent
          - Event: s3:ObjectRemoved:*
            Topic: !Ref S3ObjectChangeEvent
    DependsOn:
      - BucketToSNSPermission

  S3ObjectChangeEvent:
    Type: AWS::SNS::Topic
    Properties:
      TopicName: !Sub S3ObjectChanged-Topic-${AWS::AccountId}
  S3FileChangeFunction:
    Type: AWS::Serverless::Function
    Properties:
      FunctionName: !Sub s3-file-change-function
      CodeUri: ./s3-file-change-function
      Handler: index.handler
      Runtime: nodejs12.x
      MemorySize: 128
      Timeout: 5
      Tracing: Active
      Policies:
        - AWSXrayWriteOnlyAccess
      Events:
        Topic:
          Type: SNS
          Properties:
            Topic: !Ref S3ObjectChangeEvent
            Region: !Select
              - 3
              - !Split
                - ':'
                - !Ref S3ObjectChangeEvent

  BucketToSNSPermission:
    Type: AWS::SNS::TopicPolicy
    Properties:
      PolicyDocument:
        Version: 2012-10-17
        Statement:
          - Effect: Allow
            Principal:
              Service: s3.amazonaws.com
            Action: sns:Publish
            Resource: !Ref S3ObjectChangeEvent
            Condition:
              ArnEquals:
                aws:SourceArn: !Sub arn:${AWS::Partition}:s3:::my-bucket-${AWS::AccountId}
      Topics:
        - !Ref S3ObjectChangeEvent