Triggering Lambda function on S3 file upload

Applicable when

• Custom logic should be invoked on S3 file upload (useful with Transfer Family SFTP server)

Implementation

First, you need to create the handler lambda

import { S3CreateEvent } from 'aws-lambda';

export async function handler(event: S3CreateEvent): Promise<void> {
  await Promise.all(
    event.Records.map(async record => {
      // Filename: record.s3.object.key
    })
  );
}

Then you need to add the following CDK code

import { Bucket, EventType } from '@aws-cdk/aws-s3';
import { LambdaDestination } from '@aws-cdk/aws-s3-notifications';
import { DATA_BUCKET_TAG, withEnv } from '../util/consts';

const uploadBucketName = withEnv(DATA_BUCKET_TAG);
const uploadBucket = new Bucket(this, uploadBucketName, {
  bucketName: uploadBucketName,
});

const triggerLambda = this.lambdas.createLambda('<handler>', 'S3PutObjectTrigger');

/*
 * This will create a placeholder lambda named: <stack-name>-BucketNotificationsHandler-<id>. No clean workaround
 * yet. See: https://github.com/aws/aws-cdk/issues/2781
 */
uploadBucket.addEventNotification(EventType.OBJECT_CREATED, new LambdaDestination(triggerLambda));