Attaching an existing Lambda as a DynamoDB Table's Stream trigger so that the Lambda can see the changes as they happen in the DynamoDB Table
Let's see how to attach an existing Lambda as a DynamoDB Table Stream trigger using code. If you disable/enable DynamoDB Stream for any reason the Lambda Trigger would get disconnected and this code would reattach the Lambda trigger back. This code is written in Java
- Retrieve DynamoDB Table's Stream ARN.
String streamArn = null;
AmazonDynamoDBStreams dynamoDBStreamsClient = AmazonDynamoDBStreamsClientBuilder.standard().build();
// Create request
ListStreamsRequest listStreamRequest = new ListStreamsRequest();
listStreamRequest.setTableName(dynamoDBTable);
// Fetch Streams
ListStreamsResult response = dynamoDBStreamsClient.listStreams(listStreamRequest);
// Get the StreamARN
if (response != null && response.getStreams() != null && response.getStreams().size() > 0) {
Stream stream = response.getStreams().get(0);
streamArn = stream.getStreamArn();
}
return streamArn;
When a DynamoDB Table name is passed on to the above code, the 'listStreams' would return only a single Stream ARN, if the Table name is not passed it would return all the Table's Stream ARN.
- Attach Lambda as a Trigger for DynamoDB Table's Stream. In the below code the 'eventSourceArn' is same as the 'streamArn' we retrieved above
// create EventSourceMapping Request
CreateEventSourceMappingRequest createEventSourceMappingRequest = new CreateEventSourceMappingRequest();
// Set the Trigger enabled
createEventSourceMappingRequest.setEnabled(true);
// Set the Source of the Stream, in our case DynamoDB
createEventSourceMappingRequest.setEventSourceArn(eventSourceArn);
// Set the Starting position of the Stream to be consumed
createEventSourceMappingRequest.setStartingPosition("LATEST");
// Name of the Lambda function that gets triggered
createEventSourceMappingRequest.setFunctionName(functionName);
// Create Lambda Client
AWSLambda lambdaClient = AWSLambdaClientBuilder.standard().build();
// Execute SourceMapping request
CreateEventSourceMappingResult createEventSourceMappingResult = lambdaClient
.createEventSourceMapping(createEventSourceMappingRequest);
