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

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"
        }

Use a bucket deployment to upload a file to S3 when deploying a CDK stack

Instead of manually uploading our assets, let's create an assets folder in our todo application and upload those assets automatically.

👍 We'll be using the aws-s3-deployment deployment construct to do that.

Create an assets directory in the root of the project and add a test file to it.

Run:

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

Import it to our todo app:

import * as s3Deployment from "@aws-cdk/aws-s3-deployment";

Then add the deployment:

new s3Deployment.BucketDeployment(this, "DeployLogo", {
    destinationBucket: logoBucket,
    // an array of sources
    sources: [s3Deployment.Source.asset("./assets")]
});

Once we run cdk deploy our test file should be safe and sound in our todo s3 bucket.

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