If the application is built on top of SAM, then all of the tooling is already in place for automated deployments. You can orchestrate this with CodePipeline, which can essentially pull your code (from the code repository), pull down the required packages, create the deployment package, and build the application. You can test the application using third-party tools that are natively supported by CodePipeline.
For more details on serverless application developer tooling, refer to: http://aws.amazon.com/serverless/developer-tools.
You can use the power of SAM to deploy in multiple environments. The problem here is that there is an immediate switch from the old to the new version of the code. And ...
