The architecture of the infrastructure-as-code (IaC) tooling you use will determine the level to which your IaC definitions are exposed to bit rot.

This is a maxim I have arrived at after working with multiple IaC tool sets, both professionally and personally, over the last few years. In this blog post, I will explain how I arrived at this maxim by describing three architectural patterns for IaC tools, each with differing levels of risk for bit rot.

AWS CloudFormation is a service that lets you create a collection of related Amazon Web Services and third-party resources and provision them in an orderly and predictable fashion. A typical access control pattern is to delegate permissions for users to interact with CloudFormation and remove or limit their permissions to provision resources directly. You can grant the AWS CloudFormation service permission to create resources by creating a role that the user passes to CloudFormation when a stack or stack set is created. This can be used to ensure that only pre-authorized services and resources are provisioned in your AWS account. In this post, I show you how to conform to the principle of least privilege while still allowing users to use CloudFormation to create the resources they need.

AWS Serverless Application Model (SAM) is a framework for building serverless applications on AWS. One of the components of SAM is a template specification. SAM templates would look and feel familiar to anyone who has used AWS CloudFormation to define their infrastructure as code, however they are not completely interchangeable. There are multiple reasons why you might want to convert from SAM to native CloudFormation:

• You want to deploy the app using CloudFormation StackSets. SAM uses the AWS::Serverless transform in its templates and transforms are not supported by stack sets.
• You want to deploy the app as part of an AWS Landing Zone (ALZ) account baseline. ALZ uses stack sets as the mechanism to deploy baseline resources and so suffers from the same constraint as the point above.
• Your operating system of choice isn't documented in the SAM installation instructions and you're uncertain how to install from source or doubtful it will work at all (I'm looking at fellow OpenBSD and FreeBSD users here).

This post will show you how to take an existing SAM application and convert it to a CloudFormation template (CFT). As a CFT, the challenges listed above can be avoided.