@aws-cdk/aws-lambda-event-sources

AWS Lambda Event Sources

This module includes classes that allow using various AWS services as event sources for AWS Lambda via the high-level lambda.addEventSource(source) API.

NOTE: In most cases, it is also possible to use the resource APIs to invoke an AWS Lambda function. This library provides a uniform API for all Lambda event sources regardless of the underlying mechanism they use.

SQS

Amazon Simple Queue Service (Amazon SQS) allows you to build asynchronous workflows. For more information about Amazon SQS, see Amazon Simple Queue Service. You can configure AWS Lambda to poll for these messages as they arrive and then pass the event to a Lambda function invocation. To view a sample event, see Amazon SQS Event.

To set up Amazon Simple Queue Service as an event source for AWS Lambda, you first create or update an Amazon SQS queue and select custom values for the queue parameters. The following parameters will impact Amazon SQS's polling behavior:

• visibilityTimeoutSec: May impact the period between retries.
• receiveMessageWaitTimeSec: Will determine long poll duration. The default value is 20 seconds.

import { SqsEventSource } from '@aws-cdk/aws-lambda-event-sources';

const queue = new sqs.Queue(this, 'MyQueue', {
  visibilityTimeoutSec: 30      // default,
  receiveMessageWaitTimeSec: 20 // default
});

lambda.addEventSource(new SqsEventSource(queue, {
  batchSize: 10 // default
});

S3

You can write Lambda functions to process S3 bucket events, such as the object-created or object-deleted events. For example, when a user uploads a photo to a bucket, you might want Amazon S3 to invoke your Lambda function so that it reads the image and creates a thumbnail for the photo.

You can use the bucket notification configuration feature in Amazon S3 to configure the event source mapping, identifying the bucket events that you want Amazon S3 to publish and which Lambda function to invoke.

import { S3EventSource } from '@aws-cdk/aws-lambda-event-sources';

const bucket = new s3.Bucket(...);

lambda.addEventSource(new S3EventSource(bucket, {
  events: [ s3.EventType.ObjectCreated, s3.EventType.ObjectDeleted ],
  filters: [ { prefix: 'subdir/' } ] // optional
}));

SNS

You can write Lambda functions to process Amazon Simple Notification Service notifications. When a message is published to an Amazon SNS topic, the service can invoke your Lambda function by passing the message payload as a parameter. Your Lambda function code can then process the event, for example publish the message to other Amazon SNS topics, or send the message to other AWS services.

This also enables you to trigger a Lambda function in response to Amazon CloudWatch alarms and other AWS services that use Amazon SNS.

For an example event, see Appendix: Message and JSON Formats and Amazon SNS Sample Event. For an example use case, see Using AWS Lambda with Amazon SNS from Different Accounts.

import { SnsEventSource } from '@aws-cdk/aws-lambda-event-sources';

const topic = new sns.Topic(...);

lambda.addEventSource(new SnsEventSource(topic));

When a user calls the SNS Publish API on a topic that your Lambda function is subscribed to, Amazon SNS will call Lambda to invoke your function asynchronously. Lambda will then return a delivery status. If there was an error calling Lambda, Amazon SNS will retry invoking the Lambda function up to three times. After three tries, if Amazon SNS still could not successfully invoke the Lambda function, then Amazon SNS will send a delivery status failure message to CloudWatch.

Roadmap

Eventually, this module will support all the event sources described under Supported Event Sources in the AWS Lambda Developer Guide.