Configure event notifications using EventBridge for S3 buckets using CDK

There are two ways to configure event notifications on the S3 bucket:

1. Using EventBridge notifications. This is covered in this guide
2. Using the add_event_notification method of the Bucket construct. This is covered in the next guide

Configure EventBridge notifications

To configure EventBridge notifications, we will need to do the following:

1. Turn on sending of S3 events to EventBridge: This is a one time activity, which can be done either from console or through CDK.
2. Create an EventBridge rule: We define the rule using a pattern that specifies the event types to listen for and the targets to send the events to
3. Create an EventBridge target: We attach a target to the rule that specifies the target resource to send the events to. In this case, we will add a simple Lambda function as a target.

Import the required modules

We need to import the aws_lambda and aws_events modules to create the Lambda function and the EventBridge rule respectively.

# filename: cdk_app/s3_stack.py#part-1

from aws_cdk import (
    Stack,
    aws_s3 as s3,
    RemovalPolicy,
    aws_lambda as _lambda,
    aws_events as events,  # 👈🏽 Import the events module
    aws_events_targets as targets,  # 👈🏽 Import the events_targets module
)

from constructs import Construct

Initialise the stack and create the S3 bucket

We will initialise the stack and create the S3 bucket as we did in the previous examples. We will also turn on sending of S3 events to EventBridge.

class S3Stack(Stack):

    BUCKET_ID = "MyS3Bucket"
    EVENT_RULE_ID = "MyS3BucketEventRule"

    def __init__(self, scope: Construct, construct_id: str, **kwargs) -> None:
        super().__init__(scope, construct_id, **kwargs)

        # 👇🏽 Create the S3 bucket
        my_bucket = s3.Bucket(
            self,
            id=self.BUCKET_ID,
            removal_policy=RemovalPolicy.DESTROY,
            event_bridge_enabled=True,  # 👈🏽 Enable EventBridge notifications
        )

Create the Lambda function

We will create a simple Lambda function that prints “File uploaded” when invoked.

        # 👇🏽 Create the Lambda function
        _lambda.Function(self, 
            id="MyFirstLambda",
            runtime=_lambda.Runtime.PYTHON_3_7,
            code=_lambda.Code.from_inline("def main(event, context):\n\tprint('File Uploaded')"),
            handler="index.main",
        )

Create the EventBridge rule

We will create an EventBridge rule that listens for events from the S3 bucket and sends them to the Lambda function.

        # 👇🏽 Create an EventBridge rule
        event_rule = events.Rule(
            self,
            id=self.EVENT_RULE_ID,
            event_pattern=events.EventPattern(
                source=["aws.s3"], # 👈🏽 Listen for events from S3
                detail_type=["Object Created"], # 👈🏽 List of event types to listen for
                detail={
                    "buckets": {
                        "name": [my_bucket.bucket_name], # 👈🏽 List of buckets to listen to
                    },
                },
            ),
        )

        # 👇🏽 Add lambda function as a target for the EventBridge rule
        event_rule.add_target(targets.LambdaFunction(my_lambda_fn))

Deploy the app

After the above changes, the full code will look like this:

# filename: cdk_app/s3_stack.py

from aws_cdk import (
    Stack,
    aws_s3 as s3,
    RemovalPolicy,
    aws_lambda as _lambda,
    aws_events as events,  # 👈🏽 Import the events module
    aws_events_targets as targets,  # 👈🏽 Import the events_targets module
)

from constructs import Construct


class S3Stack(Stack):
    BUCKET_ID = "MyS3Bucket"
    EVENT_RULE_ID = "MyS3BucketEventRule"

    def __init__(self, scope: Construct, construct_id: str, **kwargs) -> None:
        super().__init__(scope, construct_id, **kwargs)

        my_bucket = s3.Bucket(
            self,
            id=self.BUCKET_ID,
            removal_policy=RemovalPolicy.DESTROY,
        )

        # 👇🏽 Create the Lambda function
        my_lambda_fn = _lambda.Function(
            self,
            id="MyLambdaFn",
            runtime=_lambda.Runtime.PYTHON_3_7,
            code=_lambda.Code.from_inline("def main(event, context):\n\tprint('File uploaded!')"),
            handler="index.main",
        )

        # 👇🏽 Create an EventBridge rule
        event_rule = events.Rule(
            self,
            id=self.EVENT_RULE_ID,
            event_pattern=events.EventPattern(
                source=["aws.s3"],
                detail_type=["Object Created"],
                detail={
                    "bucket": {
                        "name": [my_bucket.bucket_name],
                    },
                },
            ),
        )

        # 👇🏽 Add lambda function as a target for the EventBridge rule
        event_rule.add_target(targets.LambdaFunction(my_lambda_fn))

Now you can deploy the app by running cdk deploy. This will create the S3 bucket, the Lambda function and the EventBridge rule.

Test the app

Let’s upload a file to the S3 bucket and see if the Lambda function is invoked.

If you check your CloudWatch logs, you will see that the Lambda function was invoked and it printed “File uploaded!”.