This application demonstrates advanced capabilities of AWS CloudFormation Rain, a CLI tool written in Go that uses the AWS SDK to improve the developer experience for authoring and deploying CloudFormation templates.

Rain allows you to create client-side modules in YAML, so that you can re-use common patterns and speed up the development process. These modules look just like regular CloudFormation templates and can be included in a parent template using the !Rain::Module directive.

Rain also looks for special Metadata comments on the AWS::S3::Bucket resource to run external build scripts before deployment, and then to upload the contents of a folder to the newly created bucket after deployment is complete

For Lambda functions, Rain can run a script to build and/or package your handler, and then it will upload a zip file to an assets bucket before deploying the stack.

Combining these features together allows you to deploy an entire serverless web application with a single command, in this case rain deploy -x webapp.yaml