Cloudformation template to trigger Lambda on S3 event

Question

I want to use Cloudformation to create an S3 bucket that will trigger Lambda function whenever an S3 event occurs such as file creation, file deletion, etc.

From my research, I have my AWS::Lambda::Function and AWS::S3::Bucket setup,

AWSTemplateFormatVersion: '2010-09-09'
Resources:
  HandleFileCreation: 
    Type: "AWS::Lambda::Function"
    Properties: 
      ...

  LambdaExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      ManagedPolicyArns:
      - arn:aws:iam::aws:policy/AmazonS3FullAccess
      - arn:aws:iam::aws:policy/AWSLambdaFullAccess
      AssumeRolePolicyDocument:
        ...

  ReportsBucket:
    Type: AWS::S3::Bucket

  BucketPolicy:
    Type: AWS::S3::BucketPolicy
    Properties:
      Bucket: !Ref ReportsBucket
      PolicyDocument:
        ...

I was looking at the AWS::Events::Rule, but the example is only for EC2 and I can't find examples for S3

  EventRule: 
    Type: "AWS::Events::Rule"
    Properties: 
      Description: "EventRule"
      EventPattern: 
        source: 
          - "aws.ec2"
        detail-type: 
          - "EC2 Instance State-change Notification"
        detail: 
          state: 
            - "stopping"
      State: "ENABLED"
      Targets: 
        - 
          Arn: 
            Fn::GetAtt: 
              - HandleFileCreation
              - Arn
          Id: TargetFunctionV1
  PermissionForEventsToInvokeLambda: 
    Type: AWS::Lambda::Permission
    Properties: 
      FunctionName: 
        Ref: HandleFileCreation
      Action: "lambda:InvokeFunction"
      Principal: "events.amazonaws.com"
      SourceArn: 
        Fn::GetAtt: 
          - "EventRule"
          - "Arn"

How do I write the template to trigger on S3 events?

Answer 1

Here is an example covered,

http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-s3-bucket-notificationconfig-lambdaconfig.html

EncryptionServiceBucket:
  Type: "AWS::S3::Bucket"
  Properties:
    BucketName: !Sub ${User}-encryption-service
    NotificationConfiguration:
      LambdaConfigurations:
        -
          Function: !Ref LambdaDeploymentArn
          Event: "s3:ObjectCreated:*"
          Filter:
            S3Key:
              Rules:
                -
                  Name: suffix
                  Value: zip

One issue I have noticed is, you need to create the function before you assign a trigger to it. If you are doing with CF, make sure you create lambda function before you create trigger for it.

Hope it helps.

Answer 2

I found the answer in one of the Visual Studio example projects with the Amazon Toolkit:

"myBucketName": {
    "Type": "AWS::S3::Bucket",
    "Properties": { }
},
"csvProcessor" : {
  "Type" : "AWS::Serverless::Function",
  "Properties": {
    "Handler": "appli::appli.csvProcessor::FunctionHandler",
    "Runtime": "dotnetcore2.1",
    "CodeUri": "",
    "Description": "Function processing files when they're dropped in s3 bucket",
    "MemorySize": 256,
    "Timeout": 30,
    "Role": null,
    "Policies": [ "AWSLambdaFullAccess" ],
    "Events": {
        "madeUpEventName" : {
            "Type" : "S3",
            "Properties" : {
                "Bucket" : { "Ref" : "myBucketName" },
                "Events" : [
                    "s3:ObjectCreated:*"
                ]
            }
        }
    }
  }
}