Software service running on the OpenStack infrastructure measuring usage and sending the results to the collector.
API server
HTTP REST API service for ceilometer.
Billing is the process to assemble bill line items into a single per customer bill, emitting the bill to start the payment collection.
bus listener agent
Bus listener agent which takes events generated on the Oslo notification bus and transforms them into Ceilometer samples. This is the preferred method of data collection.

From Wikipedia [1]:

A ceilometer is a device that uses a laser or other light source to determine the height of a cloud base.
polling agent
Software service running either on a central management node within the OpenStack infrastructure or compute node measuring usage and sending the results to the collector.
Software service running on the OpenStack infrastructure monitoring notifications from other OpenStack components and samples from the ceilometer agent and recording the results in the database.
notification agent
The different OpenStack services emit several notifications about the various types of events. The notification agent consumes them from respective queues and filters them by the event_type.
data store
Storage system for recording data collected by ceilometer.

The measurements tracked for a resource. For example, an instance has a number of meters, such as duration of instance, CPU time used, number of disk io requests, etc. Three types of meters are defined in ceilometer:

  • Cumulative: Increasing over time (e.g. disk I/O)
  • Gauge: Discrete items (e.g. floating IPs, image uploads) and fluctuating values (e.g. number of Swift objects)
  • Delta: Incremental change to a counter over time (e.g. bandwidth delta)
Metering is the process of collecting information about what, who, when and how much regarding anything that can be billed. The result of this is a collection of “tickets” (a.k.a. samples) which are ready to be processed in any way you want.
A message sent via an external OpenStack system (e.g Nova, Glance, etc) using the Oslo notification mechanism [2]. These notifications are usually sent to and received by Ceilometer through the notifier RPC driver.

From Wikipedia [3]:

Non-repudiation refers to a state of affairs where the purported maker of a statement will not be able to successfully challenge the validity of the statement or contract. The term is often seen in a legal setting wherein the authenticity of a signature is being challenged. In such an instance, the authenticity is being “repudiated”.
The OpenStack tenant or project.
polling agents
The polling agent is collecting measurements by polling some API or other tool at a regular interval.
push agents
The push agent is the only solution to fetch data within projects, which do not expose the required data in a remotely usable way. This is not the preferred method as it makes deployment a bit more complex having to add a component to each of the nodes that need to be monitored.
Rating is the process of analysing a series of tickets, according to business rules defined by marketing, in order to transform them into bill line items with a currency value.
The OpenStack entity being metered (e.g. instance, volume, image, etc).
Data sample for a particular meter.
The origin of metering data. This field is set to “openstack” by default. It can be configured to a different value using the sample_source field in the ceilometer.conf file.
An OpenStack user.

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