eventbridge

EventBridge Patterns

Overview

Amazon EventBridge provides event-driven routing with filtering and transformation. Use it for decoupled, cross-service events (e.g. PropertyCreated → search sync, ListingSold → notifications). Prefer EventBridge over SNS when you need content-based filtering and multiple targets per event type.

CDK: Custom Event Bus and Rules

// cdk/lib/stacks/events-stack.ts

import { Stack, StackProps } from "aws-cdk-lib";
import { Construct } from "constructs";
import { EventBus, Rule } from "aws-cdk-lib/aws-events";
import { LambdaFunction } from "aws-cdk-lib/aws-events-targets";
import { StandardLambda } from "../constructs/lambda-function";
import { Table } from "aws-cdk-lib/aws-dynamodb";

interface EventsStackProps extends StackProps {
  dataTable: Table;
  opensearchEndpoint: string;
}

export class EventsStack extends Stack {
  public readonly domainBus: EventBus;

  constructor(scope: Construct, id: string, props: EventsStackProps) {
    super(scope, id, props);

    this.domainBus = new EventBus(this, "RealEstateDomainBus", {
      eventBusName: "real-estate-domain",
    });

    const searchIndexerFn = new StandardLambda(this, "SearchIndexer", {
      entry: "src/functions/sync-search/handler.ts",
      handler: "handler",
      memorySize: 512,
      timeoutSeconds: 30,
      environment: {
        EVENT_BUS_NAME: this.domainBus.eventBusName,
        OPENSEARCH_ENDPOINT: props.opensearchEndpoint,
        DYNAMODB_TABLE_NAME: props.dataTable.tableName,
      },
    });
    props.dataTable.grantReadData(searchIndexerFn);

    new Rule(this, "PropertyEventsToSearch", {
      eventBus: this.domainBus,
      ruleName: "property-events-to-search",
      eventPattern: {
        source: ["real-estate.property"],
        detailType: ["PropertyCreated", "PropertyUpdated", "PropertyDeleted"],
      },
      targets: [new LambdaFunction(searchIndexerFn)],
    });

    const notifierFn = new StandardLambda(this, "ListingNotifier", {
      entry: "src/functions/listing-notifier/handler.ts",
      handler: "handler",
      memorySize: 256,
      timeoutSeconds: 10,
      environment: { EVENT_BUS_NAME: this.domainBus.eventBusName },
    });
    new Rule(this, "ListingSoldToNotifier", {
      eventBus: this.domainBus,
      ruleName: "listing-sold-to-notifier",
      eventPattern: {
        source: ["real-estate.listing"],
        detailType: ["ListingSold"],
      },
      targets: [new LambdaFunction(notifierFn)],
    });
  }
}