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Lambdas with API Gateway - CDK

This sample project displays how to create AWS Lambdas behind an API Gateway using CDK.

Structure

The structure of this project is meant to have the actual domain logic loosely coupled to the AWS and HTTP specifics. All domain logic is in the commands module, which then depends on the kernel module. This means that we have to transform the payloads and response that are send to or comes from the commands module to work with the ones expected by the the Lambda runtime, which is achieved through the aws module in this project (see makeLambdaHandler at aws/index.ts);

External dependencies (NPM)

The Lambda packager/builder is smart enough to only pick up the dependencies needed by each specific Lambda Function. For example, the SumNumbers function uses the bignumber.js NPM package to perform its (very advanced) calculation, and even though this dependency comes from node_modules in the root of the source code, when we build the CloudFormation Stack, this module is only included in the SumNumbers Lambda.

Pros & Cons

Pros

  • clean microservices-oriented architecture;
  • clear separation between Domain and Transformations;
  • less costs as we only pay per execution time;
  • much less infra to manage;
  • auto-scaling, caching, monitoring...;
  • (as) easy (as possible) to switch to different cloud providers or self-hosting;

Cons

  • more complex code than running express behind the Lambda or in an EC2;
  • more code as we need transaformers 🤖🦾🦿;
  • more complex deployment process;