how-to-trigger-lambda-from-s3-stack.ts

// Import aws-cdk packages
import * as cdk from '@aws-cdk/core';
import * as s3 from '@aws-cdk/aws-s3';
import * as lambda from '@aws-cdk/aws-lambda';
import * as lambdaEventSources from '@aws-cdk/aws-lambda-event-sources';

export class HowToTriggerLambdaFromS3Stack extends cdk.Stack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    // Create a new S3 bucket
    const bucket = new s3.Bucket(this, 'OurBucket', {
      /**
       * The following properties ensure the bucket is properly 
       * deleted when we run cdk destroy */
      autoDeleteObjects: true,
      removalPolicy: cdk.RemovalPolicy.DESTROY
    });

    // Create a new Lambda Function
    const lambdaFunction = new lambda.Function(this, 'Function', {
      code: lambda.Code.fromAsset('src'),
      handler: 'index.handler',
      functionName: 'BucketPutHandler',
      runtime: lambda.Runtime.NODEJS_12_X,
    });

    // Create a new S3 Event Source
    const s3PutEventSource = new lambdaEventSources.S3EventSource(bucket, {
      events: [
        s3.EventType.OBJECT_CREATED_PUT
      ]
    });

    // Attach the S3 event source to the Lambda Function
    lambdaFunction.addEventSource(s3PutEventSource);
  }
}