A developer is deploying an existing Lambda function whose deployment package and dependencies are stored in Amazon S3 using an AWS CloudFormation template. The CloudFormation template defines an AWS::Lambda::Function resource. What is the minimal-effort way to reference the function code stored in S3 within the template?

To reference an existing Lambda function's deployment package stored in S3, the AWS::Lambda::Function resource in CloudFormation requires the S3Bucket and S3Key properties. These properties directly specify the S3 bucket name and the object key (path) where the .zip file containing the function code and dependencies is located. This is the most straightforward and minimal-effort approach for this scenario. Embedding the code inline or using the ZipFile property with inline code is not suitable for an existing deployment package stored in S3, as these methods are for defining the code directly within the template, not referencing an external S3 object. Using the S3 key value as the ZipFile property is incorrect because ZipFile expects the actual code content, not an S3 key.