Amazon SageMaker Ground Truth now allows you to measure and track the throughput and efficiency of your own private workers performing data labeling. During the course of a labeling job, Amazon SageMaker Ground Truth logs all private worker events (for example, when a labeler starts and submits a task) to Amazon CloudWatch. In addition, you can also use the built-in metrics feature of CloudWatch to measure and track throughput across a work team or for individual workers.  

from Recent Announcements https://aws.amazon.com/about-aws/whats-new/2019/09/amazon-sagemaker-ground-truth-supports-private-worker-throughput-worker-logs-metrics/