13-create-an-s3-event-notification-to-trigger-a-lambda-function-on-file-upload.md

Create an S3 event notification to trigger a lambda function on file upload

📹 Video

Let's trigger our lambda function every time we upload a file to our s3 bucket.

We'll need to install s3 notifications.

Run:

• npm install --save @aws-cdk/aws-s3-notifications

Import it to our stack file:

• import * as s3Notifications from @aws-cdk/aws-s3-notifications;

and then:

// attaching a notification to our logo bucket
logoBucket.addEventNotification(
    // every time a new file is added to our bucket
    s3.EventType.OBJECT_CREATED,
    // execute our lambda function
    new s3Notifications.LambdaDestination(helloLambda)
);

👍 Tip: Make sure you have npm run watch running in another terminal tab - this will let you know if there are any typescript errors.

In the aws console, go to Services and search for s3. Upload a file to the bucket then check if the lambda function was triggered by going back to Services and looking for lambda.

👍 You can see your recently accessed aws dashboards in the History sidebar on the left.

In your lambda dashboard notice how a new function was added (for me it was: TodoAppStack-BucketNotificationsHandler050a0587b75-1BQ2LOUD7KPXI).

Click on the HelloLambda function, then click Monitoring and View logs in CloudWatch.

Then click on the latest log and expand the event log (it will mention things like eventVersion, eventSource etc) and look for the information about your recently uploaded image.

Mine looked like this:

"object": {
            "key": "Screenshot+2020-05-13+at+07.24.34.png",
            "size": 19145,
            "eTag": "40502d42d31dab5fe8581bd3d7ce0202",
            "sequencer": "005EBCD5882BF314F4"
        }