New measurements

Ceilometer is designed to collect measurements from OpenStack services and from other external components. If you would like to add new meters to the currently existing ones, you need to follow the guidelines given in this section.

Types

Three type of meters are defined in Ceilometer:

Type	Definition
Cumulative	Increasing over time (instance hours)
Gauge	Discrete items (floating IPs, image uploads) and fluctuating values (disk I/O)
Delta	Changing over time (bandwidth)

When you’re about to add a new meter choose one type from the above list, which is applicable.

Units

1. Whenever a volume is to be measured, SI approved units and their approved symbols or abbreviations should be used. Information units should be expressed in bits (‘b’) or bytes (‘B’).
2. For a given meter, the units should NEVER, EVER be changed.
3. When the measurement does not represent a volume, the unit description should always describe WHAT is measured (ie: apples, disk, routers, floating IPs, etc.).
4. When creating a new meter, if another meter exists measuring something similar, the same units and precision should be used.
5. Meters and samples should always document their units in Ceilometer (API and Documentation) and new sampling code should not be merged without the appropriate documentation.

Dimension	Unit	Abbreviations	Note
None	N/A		Dimension-less variable
Volume	byte	B
Time	seconds	s

Meters

Naming convention

If you plan on adding meters, please follow the convention below:

1. Always use ‘.’ as separator and go from least to most discriminant word. For example, do not use ephemeral_disk_size but disk.ephemeral.size
2. When a part of the name is a variable, it should always be at the end and start with a ‘:’. For example, do not use <type>.image but image:<type>, where type is your variable name.
3. If you have any hesitation, come and ask in #openstack-ceilometer

Meter definitions

Meters definitions by default, are stored in separate configuration file, called ceilometer/meter/data/meter.yaml. This is essentially a replacement for prior approach of writing notification handlers to consume specific topics.

A detailed description of how to use meter definition is illustrated in the admin_guide.

Non-metric meters and events

Ceilometer supports collecting notifications as events. It is highly recommended to use events for capturing if something happened in the system or not as opposed to defining meters of which volume will be constantly ‘1’. Events enable better representation and querying of metadata rather than statistical aggregations required for Samples. When the event support is turned on for Ceilometer, event type meters are collected into the event database too, which can lead to the duplication of a huge amount of data.

In order to learn more about events see the Events and Event Processing section.