AWS CDK VS SDK for IaC

AWS SDK is a library primarily to ease the access to the AWS services by handling for you the data (de)serialization, credentials management, failure handling, etc. Perhaps, for specific scenarios, you could use the AWS SDK as the infrastructure as a code tool, however it could be cumbersome as it is not the intended usage of the library.

Based on the https://docs.aws.amazon.com/whitepapers/latest/develop-deploy-dotnet-apps-on-aws/infrastructure-as-code.html, dedicated tools for the IaC are AWS CloudFormation and AWS CDK.

AWS CDK is an abstraction on top of CloudFormation. CDK scripts are in fact transformed to the CloudFormation definitions when scripts are synthesized.

The difference can be best described on an example: Imagine that for each lambda function in your stack you want to create an error CloudWatch alarm and connect to the SNS topic.

With CloudFormation you will either a) need to write a pretty much similar bunch of yaml/json definitions for each lambda function to ensure the monitoring, b) use the nested stack templates, c) use CloudFormation modules.

With CDK you can write a generic code construct - class or method, which can create the alarm for the given lambda function and create the SNS alarm action for given topic.

In other words, CDK helps you generalize and re-use your IaC in a very familiar way to how you develop your business code. The code is shorter and more readable than the CF definitions.

The difference is even more remarkable when you need to set up similar resources in different AWS regions and when you have different AWS account per environment. You can manage all AWS accounts and regions with a single CDK codebase.