Lookup S3 Bucket and add a trigger to invoke a lambda

Question

I'm using the new AWS CDK(Cloud Development Toolkit) to build the infrastructure on AWS in Java.

What I have to do: lookup an s3 bucket and add a trigger that invokes a lambda function.

What I have done:

Looked up s3 bucket:

IBucket bucket = Bucket.fromBucketName(scope, bucketId, bucketName);

Add a new event source to the existing lambda:

IEventSource eventSource = getObjectCreationEvent();
lambda.addEventSource(eventSource);

Where getObjectCreationEvent() is:

private S3EventSource getObjectCreationEvent() {
    return new S3EventSource(bucket, new S3EventSourceProps() {
        @Override
        public List<EventType> getEvents() {
            return Collections.singletonList(EventType.OBJECT_CREATED);
        }
    });
}

What is the problem:

The type of bucket parameter in the S3EventSource constructor is Bucket but every lookup method (e.g. the Bucket.fromBucketName()) returns an IBucket and not a Bucket, so there is a signature mismatch. If I cast IBucket to Bucket I have a ClassCastException.

Not the solution you are looking for, but as a work around you could have the s3Bucket+Trigger created as an infrastructure project. Make sure that you have your lambda created beforehand, though. — thoroc

Tschallacka Tschallacka · Accepted Answer · 2020-02-24T09:35:43

From the git issue tracker https://github.com/aws/aws-cdk/issues/2004#issuecomment-479923251

Due to current limitations with CloudFormation and the way we implemented bucket notifications in the CDK, it is impossible to add bucket notifications on an imported bucket. This is why the event source uses s3.Bucket instead of s3.IBucket.

You could use onPutObject:

const bucket = s3.Bucket.import(this, 'B', {
  bucketName: 'my-bucket'
});

const fn = new lambda.Function(this, 'F', {
  code: lambda.Code.inline('boom'),
  runtime: lambda.Runtime.NodeJS810,
  handler: 'index.handler'
});

bucket.onPutObject('put-object', fn);

But reading further on, this doesn't seem to work anymore either.

It seems the answer currently is:

It's impossible to set up.

Lookup S3 Bucket and add a trigger to invoke a lambda

1 Answers