What service is in charge of telemetry on OpenStack?

The correct choice is D, Celiometer, because it is the official telemetry service in OpenStack, designed to collect and store performance metrics and events from various components of the OpenStack ecosystem as well as the applications running on top of it. Telemetry refers to the collection of data from various sources, and Celiometer provides functionality to monitor and measure resource usage across the cloud infrastructure, capturing data such as usage statistics over time, alerts, and other metrics important for billing and monitoring purposes.

Celiometer plays a crucial role in OpenStack's ability to provide advanced features such as metering, monitoring, and event notifications, which are essential for cloud management and operation. It integrates with other OpenStack services to gather data efficiently and supports various APIs to allow users to access this information. By leveraging Celiometer, users can gain insights into resource consumption and optimize their deployments accordingly, which is critical for efficient cloud resource management and billing systems.

The other options listed do not pertain directly to the telemetry functionality essential to managing and monitoring the OpenStack environment.