CDK app that deploys a Lambda function from a hybrid ESM bundle.
This repository demonstrates a hybrid approach to optimize Node.js Lambda functions by leveraging the advantages of ES modules (ESM) for size and performance improvements, while maintaining compatibility with existing CommonJS (CJS) codebases.
The Dilemma: Transitioning a project entirely to ESM can be a daunting task, often hindered by dependencies on older CJS libraries and the complexities of updating project configurations. This typically involves modifications to tsconfig.json
, package.json
, and cdk.json
files, which can be time-consuming and error-prone.
The Hybrid Approach: By leveraging the AWS CDK's NodejsFunction construct and its built-in esbuild
bundling capabilities, we can create Lambda functions that prioritize ESM modules while gracefully falling back to CJS when needed. This enables us to achieve the following benefits::
- Significant Size Reduction: Witness dramatic reductions in package size compared to traditional CJS bundling, thanks to ESM features like tree-shaking, which eliminates unused code. For instance, in the provided example, a CJS bundle reduces from 2.9 MB to 1.3 MB, while the hybrid ESM approach achieves an even more impressive reduction from 2.5 MB to a mere 585 KB.
- Faster Cold Starts: Smaller package size directly translates to faster Lambda initialization and significantly reduced cold start latency, improving the responsiveness and efficiency of your serverless applications.
- Enhanced Runtime Efficiency: ESM, with its support for top-level await and asynchronous module loading, can improve how your code executes and utilizes resources during runtime compared to CJS.
Key Benefits:
- Minimal Effort: No need to refactor your existing CJS codebase, saving you time and effort.
- Reduced Complexity: Avoid the intricacies of configuring your project for full ESM adoption.
- Optimized Lambda Functions: Achieve smaller package sizes and faster cold starts without sacrificing compatibility.
Implementation Details:
The provided example showcases how to configure the CDK's NodejsFunction
construct with specific bundling options to achieve this hybrid approach. Key properties include:
format
: Sets the output format to ESM for optimal bundling.mainFields
: Specifies the order in which module formats are resolved, prioritizing ESM.banner
: Includes a code snippet to ensure seamless compatibility with CJS modules.
This hybrid solution offers the best of both worlds: it unlocks ESM's size and performance benefits for your Lambda functions, while ensuring seamless integration with your existing CJS codebase, all without requiring a full migration.
- AWS:
- Must have authenticated with Default Credentials in your local environment.
- Must have completed the CDK bootstrapping for the target AWS environment.
- Node.js + npm:
- Must be installed in your system.
npx projen install
npx projen deploy
npx projen destroy