Ceilometer is the telemetry service component in the OpenStack cloud computing platform. It is responsible for collecting and processing various measurements and metrics from different OpenStack services, such as compute, storage, and networking components. Ceilometer collects data related to resource utilization, performance, and other relevant metrics, which can be used for billing, capacity planning, and troubleshooting purposes.
The ceilometer-agent-compute is a specific component of Ceilometer that runs on each compute node in an OpenStack deployment. Its primary role is to collect measurements and metrics related to the compute resources and instances running on the compute node. It gathers data about CPU usage, memory usage, network traffic, disk I/O, and other relevant statistics. The ceilometer-agent-compute communicates with the hypervisor layer on the compute node, which can be either the KVM hypervisor (using libvirt) or the Xen hypervisor (using XenAPI). It utilizes the capabilities provided by the hypervisor to collect data about the compute resources and virtual machine instances.
Here are some key features and functions of ceilometer-agent-compute:
- Polling: The agent periodically polls the hypervisor and collects resource usage data, such as CPU utilization, memory usage, and disk I/O statistics. The polling frequency can be configured based on the desired level of granularity and performance requirements.
- Event-based notifications: In addition to polling, the agent subscribes to event notifications from the hypervisor. These notifications are triggered when significant events occur, such as instance creation, deletion, or resizing. By capturing these events, the agent can provide real-time updates about the state and lifecycle of the instances.
- Metering: The agent processes the collected data and transforms it into meaningful metrics known as meters. These meters represent different aspects of resource usage, such as CPU utilization percentage, network bytes transferred, or disk read/write operations. The agent associates each meter with the corresponding instance and stores the collected data in the Ceilometer database.
- Data collection pipeline: The ceilometer-agent-compute is part of a larger data collection pipeline in Ceilometer. Once the data is collected and processed by the agent, it is sent to the Ceilometer central component (collector) for further processing and storage. The collector aggregates and stores the data in a database, such as MongoDB or an SQL database, depending on the Ceilometer configuration.
- Integration with other OpenStack services: The ceilometer-agent-compute integrates with other OpenStack services to provide a comprehensive monitoring and telemetry solution. It can interact with the Identity service (Keystone) to authenticate and authorize its operations. It also communicates with the Image service (Glance) to retrieve metadata about the instances being monitored. Additionally, it can interact with the Telemetry service (Aodh) to trigger alarms based on predefined thresholds and policies.
Overall, the ceilometer-agent-compute plays a crucial role in monitoring and collecting data about the compute resources and instances in an OpenStack deployment. By gathering and processing this information, it enables administrators and operators to make informed decisions about resource allocation, performance optimization, and capacity planning within their OpenStack cloud infrastructure.