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#S3

#Simple event definition

This will create a photos bucket which fires the resize function when an object is added or modified inside the bucket. A hardcoded bucket name can lead to issues as a bucket name can only be used once in S3. For that you can use the Serverless Variable syntax and add dynamic elements to the bucket name.

functions:
  resize:
    handler: resize.handler
    events:
      - s3: photos

#Setting the specific trigger event

This will create a bucket photos. The users function is called whenever an object is removed from the bucket. Check out the AWS documentation to learn more about all the different event types that can be configured.

functions:
  users:
    handler: users.handler
    events:
      - s3:
          bucket: photos
          event: s3:ObjectRemoved:*

#Setting filter rules

This will create a bucket photos. The users function is called whenever an image with .jpg extension is uploaded to folder uploads in the bucket. Check out the AWS documentation to learn more about all the different filter types that can be configured.

functions:
  users:
    handler: users.handler
    events:
      - s3:
          bucket: photos
          event: s3:ObjectCreated:*
          rules:
            - prefix: uploads/
            - suffix: .jpg

#Triggering separate functions from the same bucket

You're able to repeat the S3 event configuration in the same or separate functions so one bucket can call these functions. One caveat though is that you can't repeat the same configuration in both functions, e.g. the event type has to be different.

The following example will work:

functions:
  users:
    handler: users.handler
    events:
      - s3:
          bucket: photos
          event: s3:ObjectCreated:*
      - s3:
          bucket: photos
          event: s3:ObjectRemoved:*

#Custom bucket configuration

If you need to configure the bucket itself, you'll need to create the bucket and the Lambda Permission manually in the Resources section while paying attention to some of the logical IDs. This relies on the Serverless naming convention. See the Serverless Resource Reference for details. These are the logical IDs that require your attention:

  • The logical ID of the custom bucket in the Resources section needs to match the bucket name in the S3 event after the Serverless naming convention is applied to it.
  • The Lambda Permission's logical ID needs to match the Serverless naming convention for Lambda Permissions for S3 events.
  • The FunctionName in the Lambda Permission configuration needs to match the logical ID generated for the target Lambda function as determined by the Serverless naming convention.

The following example will work:

functions:
  resize:
    handler: resize.handler
    events:
      - s3: photos

resources:
  Resources:
    S3BucketPhotos:
      Type: AWS::S3::Bucket
      Properties:
        BucketName: my-custom-bucket-name
        # add additional custom bucket configuration here
    ResizeLambdaPermissionPhotosS3:
      Type: "AWS::Lambda::Permission"
      Properties:
        FunctionName:
          "Fn::GetAtt":
            - ResizeLambdaFunction
            - Arn
        Principal: "s3.amazonaws.com"
        Action: "lambda:InvokeFunction"
        SourceAccount:
          Ref: AWS::AccountId
        SourceArn: "arn:aws:s3:::my-custom-bucket-name"