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 and after deployment, and then upload the contents of a folder to the newly created bucket after deployment is complete. This allows you to so things like build your web site and even fix its configuration so that the web site knows the URL of the API Gateway, all in one step without having to do multiple deployments.

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.

TODO: Architecture diagram

TODO: Sequence of operations

TODO: Template snippets