The optionalTransform section specifies one or more macros that CloudFormation uses to process your template in some way.

Macros can perform simple tasks like finding and replacing text, or they can make more extensive transformations to the entire template. CloudFormation executes macros in the order that they're specified. When you create a change set, CloudFormation generates a change set that includes the processed template content. You can then review the changes and execute the change set. For more information about how macros work, seePerform custom processing on CloudFormation templates with template macros.

CloudFormation also supportstransforms, which are macros hosted by CloudFormation. CloudFormation treats these transforms the same as any macros you create in terms of execution order and scope. For more information, seeTransform reference.

To declare multiple macros, use a list format and specify one or more macros.

For example, in the template sample below, CloudFormation evaluatesMyMacro and thenAWS::Serverless, both of which can process the contents of the entire template because of their inclusion in theTransform section.

# Start of processable content for MyMacro and AWS::ServerlessTransform:  - MyMacro  - 'AWS::Serverless'Resources:  WaitCondition:    Type: AWS::CloudFormation::WaitCondition  MyBucket:    Type: AWS::S3::Bucket    Properties:       BucketName:amzn-s3-demo-bucket      Tags:[{"key":"value"}]      CorsConfiguration:[]  MyEc2Instance:    Type: AWS::EC2::Instance     Properties:      ImageId:ami-1234567890abcdef0# End of processable content for MyMacro and AWS::Serverless

Thanks for letting us know we're doing a good job!

If you've got a moment, please tell us what we did right so we can do more of it.

Thanks for letting us know this page needs work. We're sorry we let you down.

If you've got a moment, please tell us how we can make the documentation better.