From distributed monolith to composable architecture on AWS: A modern approach to scalable software

Aim to reduce inter-service dependencies by identifying:

• Shared databases that need decoupling.
• Synchronous calls that can be turned into asynchronous messaging.
• Code or library dependencies crossing service boundaries.

2. Separate and modularize codebase

Refactor the code into separate repositories or modules, each representing a bounded context or microservice. This clear separation supports independent deployment pipelines and ownership.

import * as cdk from 'aws-cdk-lib';
import * as lambda from 'aws-cdk-lib/aws-lambda';
import * as apigw from 'aws-cdk-lib/aws-apigateway';

export class OrderServiceStack extends cdk.Stack {
  constructor(scope: cdk.App, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const orderLambda = new lambda.Function(this, 'OrderHandler', {
      runtime: lambda.Runtime.NODEJS_18_X,
      handler: 'order.handler',
      code: lambda.Code.fromAsset('lambda/order-service'),
    });

    new apigw.LambdaRestApi(this, 'OrderAPI', {
      handler: orderLambda,
      restApiName: 'Order Service',
    });
  }
}

Consolidate infra-as-code with AWS CDK to manage each microservice’s infrastructure, including APIs, storage and permissions.