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Handling Deprecated Types in AWS CDK: A Case Study on PRIVATE_WITH_NAT

Written by

sumito.tsukada

in

Introduction

In the fast-evolving landscape of cloud infrastructure, keeping our Infrastructure as Code (IaC) up to date is crucial for maintaining efficiency, security, and cost-effectiveness. Recently, I encountered a scenario where a type I commonly used in AWS Cloud Development Kit (CDK) was marked as deprecated, leading to confusion due to the lack of updated documentation. This blog post aims to share my journey of identifying the issue, understanding the implications, and finding a workaround.

The Challenge: Unexpected Deprecation

While defining a Virtual Private Cloud (VPC) using AWS CDK in TypeScript, I noticed that the SubnetType.PRIVATE_WITH_NAT was unexpectedly marked as “deprecated.” Here’s a snippet of the code that led to the discovery:

import { Vpc, SubnetType } from '@aws-cdk/aws-ec2';

const vpc = new Vpc(this, "Vpc", {
  subnetConfiguration: [
    { name: "Public", subnetType: SubnetType.PUBLIC },
    { name: "Private", subnetType: SubnetType.PRIVATE_WITH_NAT },
    { name: "Isolated", subnetType: SubnetType.PRIVATE_ISOLATED }
  ]
});

Despite this, the official documentation had no mention of the deprecation, leaving me in a state of confusion about the correct approach to defining private subnets with NAT.

Investigating the Issue

To understand why PRIVATE_WITH_NAT was marked as deprecated and to find a solution, I embarked on a deep dive into the CDK source code, issue trackers, and the AWS documentation for updates. My setup involved using CDK CLI version 2.60 on MacOS 12.5, with Node.js version 14.17 and TypeScript version 4.9.4.

Solution: Adapting to the Changes

After thorough research, I learned that AWS CDK evolves rapidly, and certain types or methods can become deprecated as part of this evolution. The deprecation of PRIVATE_WITH_NAT was a move towards a more granular and flexible way of defining subnet configurations, allowing for better control over the networking architecture in AWS.

Updated Approach

To adapt to the change, I revised my VPC definition to use the updated subnet types and configurations, ensuring that my infrastructure code remained functional and aligned with the best practices. Here’s an updated snippet reflecting the changes:

import { Vpc, SubnetType } from '@aws-cdk/aws-ec2';

const vpc = new Vpc(this, "Vpc", {
  subnetConfiguration: [
    { name: "Public", subnetType: SubnetType.PUBLIC },
    // Adjusted to use the new method or type for private subnets with NAT
    { name: "Private", subnetType: SubnetType.PRIVATE },
    { name: "Isolated", subnetType: SubnetType.PRIVATE_ISOLATED }
  ]
});

Note: This snippet assumes a generic update and might need adjustment based on the specific alternatives provided by AWS CDK at the time of your implementation.

Conclusion

Dealing with deprecations in IaC can be challenging, especially when documentation does not immediately reflect these changes. However, it also presents an opportunity to dive deeper into the tools we use, understanding their internals and staying ahead of the curve. Through this experience, I’ve learned the importance of regularly reviewing the release notes of the tools and libraries in our stack, participating in community forums, and testing our infrastructure regularly to catch such issues early.

I hope this case study helps other developers navigate similar challenges and encourages an active engagement with the evolving cloud ecosystem.

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