From Custom Resources to Constructs: Designing a CDK Library for Serverless UDP
We recently shipped @proxylity/cdk-udp-gateway , an AWS CDK construct library for Proxylity UDP Gateway . This article presents how it was designed and built — what the library does, and the method we used to get it right: the layering strategy, the two design problems that shaped the API, the verification discipline that caught issues before they shipped, and the unglamorous engineering…
Amazon Web Services (AWS) Cloud Development Kit (CDK) enables developers to define cloud infrastructure using programming languages such as TypeScript, Python, Java, C#, Go, etc. Instead of using declarative CloudFormation JSON or YAML, CDK constructs are reusable, typed building blocks that are composed into stacks. These constructs synthesize CloudFormation templates, making it easier to build and share higher-level abstractions.
CDK constructs are conventionally described at three levels: L1 represents a 1:1 mechanical mirror of the underlying CloudFormation resource with no opinions or defaults beyond what the resource itself applies; L2 is an ergonomic, opinionated wrapper with sensible defaults, typed references, enums instead of magic strings, and automatically-derived IAM; L3 comprises full solution patterns that wire several resources together for complete use cases.
Proxylity UDP Gateway brings UDP into the serverless world, providing a managed listener endpoint for UDP, WireGuard, or DTLS, and delivering inbound datagrams to AWS destinations (Lambda, SQS, Kinesis, Firehose, S3, Step Functions, and more) as batched events. Previously, developers provisioned a listener through CloudFormation custom resources, which worked well but involved careful adherence to syntax and boilerplate.
Over two years, the service matured and stabilized, making it a good target for building a dependable abstraction on top of it. The stable contract served as the precondition for improving developer experience by letting people express a UDP service in a few lines of typed code rather than a hundred lines of JSON.
The design and building of @proxylity/cdk-udp-gateway, an AWS CDK construct library for Proxylity UDP Gateway, involved two main principles: building a faithful L1 layer first and keeping it as a distinct, permanent layer underneath L2, and verifying against reality by treating the deployed service's actual behavior as the single source of authority.
The library underwent a golden synth-diff, testing the abstraction against known-good example templates, and reviewing blocks on unverified claims. When the opinions of L2 didn't fit a specific case, developers could drop to L1 without leaving the library. This approach ensured both ease of use and transparency in the library.
Written by urgent.news from Dev.to's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
