Final answer:
AWS Lambda itself processes shard data when triggered by services like AWS Kinesis, handling data from each shard in parallel.
Step-by-step explanation:
The entity responsible for processing shard data in AWS Lambda is AWS Lambda itself. AWS Lambda functions can be triggered by AWS services such as AWS Kinesis, where the data is sharded. When a Lambda function is set up with an event source mapping to an AWS Kinesis stream, Lambda processes each shard’s data in parallel, ensuring that each record contained in the shard is processed exactly once. AWS Kinesis is the service that provides the sharded stream of data, whereas AWS Lambda processes the data from each shard, executing the code in response to triggers.