openstack-manuals/doc/admin-guide-cloud/source/telemetry-data-collection.rst

Data collection

The main responsibility of Telemetry in OpenStack is to collect information about the system that can be used by billing systems or interpreted by analytic tooling. The original focus, regarding to the collected data, was on the counters that can be used for billing, but the range is getting wider continuously.

Collected data can be stored in the form of samples or events in the supported databases, listed in telemetry-supported-databases.

Samples can have various sources regarding to the needs and configuration of Telemetry, which requires multiple methods to collect data.

The available data collection mechanisms are:

Notifications

Processing notifications from other OpenStack services, by consuming messages from the configured message queue system.

Polling

Retrieve information directly from the hypervisor or from the host machine using SNMP, or by using the APIs of other OpenStack services.

RESTful API

Pushing samples via the RESTful API of Telemetry.

Notifications

All the services send notifications about the executed operations or system state in OpenStack. Several notifications carry information that can be metered, like the CPU time of a VM instance created by OpenStack Compute service.

The Telemetry module has a separate agent that is responsible for consuming notifications, namely the notification agent. This component is responsible for consuming from the message bus and transforming notifications into events and measurement samples. Beginning in the Liberty release, the notification agent is responsible for all data processing such as transformations and publishing. After processing, the data is sent via AMQP to the collector service or any external service, which is responsible for persisting the data into the configured database back end.

The different OpenStack services emit several notifications about the various types of events that happen in the system during normal operation. Not all these notifications are consumed by the Telemetry module, as the intention is only to capture the billable events and notifications that can be used for monitoring or profiling purposes. The notification agent filters by the event type, that is contained by each notification message. The following table contains the event types by each OpenStack service that are transformed to samples by Telemetry.

OpenStack service	Event types	Note
OpenStack Compute	scheduler.run_instance.scheduled scheduler.select_destinations compute.instance.*	For a more detailed list of Compute notifications please check the System Usage Data Data wiki page <https://wiki .openstack.org/wiki/ SystemUsageData>__.
Bare metal service	hardware.ipmi.*
OpenStack Image service	image.update image.upload image.delete image.send	The required configuration for Image service can be found in Configure the Image service for Telemetry section <http://docs.openstack.org /kilo/install-guide/install /apt/content/ceilometer- glance.html>__ section in the OpenStack Installation Guide.
OpenStack Networking	floatingip.create.end floatingip.update.* floatingip.exists network.create.end network.update.* network.exists port.create.end port.update.* port.exists router.create.end router.update.* router.exists subnet.create.end subnet.update.* subnet.exists l3.meter
Orchestration module	orchestration.stack.create.end orchestration.stack.update.end orchestration.stack.delete.end orchestration.stack.resume.end orchestration.stack.suspend.end
OpenStack Block Storage	volume.exists volume.create.* volume.delete.* volume.update.* volume.resize.* volume.attach.* volume.detach.* snapshot.exists snapshot.create.* snapshot.delete.* snapshot.update.*	The required configuration for Block Storage service can be found in the Add the Block Storage service agent for Telemetry section <http: //docs.openstack.org/kilo/ install-guide/install/apt/ content/ceilometer-cinder .html>__ section in the OpenStack Installation Guide.

Note

Some services require additional configuration to emit the notifications using the correct control exchange on the message queue and so forth. These configuration needs are referred in the above table for each OpenStack service that needs it.

Specific notifications from the Compute service are important for administrators and users. Configuring nova_notifications in the nova.conf file allows administrators to respond to events rapidly. For more information on configuring notifications for the compute service, see Chapter 11 on Telemetry services <http://docs.openstack.org/ kilo/install-guide/install/apt/content/ceilometer-nova.html>__ in the OpenStack Installation Guide.

Note

When the store_events option is set to True in ceilometer.conf, Prior to the Kilo release, the notification agent needed database access in order to work properly.

Middleware for the OpenStack Object Storage service

A subset of Object Store statistics requires additional middleware to be installed behind the proxy of Object Store. This additional component emits notifications containing data-flow-oriented meters, namely the storage.objects.(incoming|outgoing).bytes values. The list of these meters are listed in telemetry-object-storage-meter, marked with notification as origin.

The instructions on how to install this middleware can be found in Configure the Object Storage service for Telemetry section in the OpenStack Installation Guide.

Telemetry middleware

Telemetry provides the capability of counting the HTTP requests and responses for each API endpoint in OpenStack. This is achieved by storing a sample for each event marked as audit.http.request, audit.http.response, http.request or http.response.

It is recommended that these notifications be consumed as events rather than samples to better index the appropriate values and avoid massive load on the Metering database. If preferred, Telemetry can consume these events as samples if the services are configured to emit http.* notifications.

Polling

The Telemetry module is intended to store a complex picture of the infrastructure. This goal requires additional information than what is provided by the events and notifications published by each service. Some information is not emitted directly, like resource usage of the VM instances.

Therefore Telemetry uses another method to gather this data by polling the infrastructure including the APIs of the different OpenStack services and other assets, like hypervisors. The latter case requires closer interaction with the compute hosts. To solve this issue, Telemetry uses an agent based architecture to fulfill the requirements against the data collection.

There are three types of agents supporting the polling mechanism, the compute agent, the central agent, and the IPMI agent. Under the hood, all the types of polling agents are the same ceilometer-polling agent, except that they load different polling plug-ins (pollsters) from different namespaces to gather data. The following subsections give further information regarding the architectural and configuration details of these components.

Running ceilometer-agent-compute is exactly the same as:

$ ceilometer-polling --polling-namespaces compute

Running ceilometer-agent-central is exactly the same as:

$ ceilometer-polling --polling-namespaces central

Running ceilometer-agent-ipmi is exactly the same as:

$ ceilometer-polling --polling-namespaces ipmi

In addition to loading all the polling plug-ins registered in the specified namespaces, the ceilometer-polling agent can also specify the polling plug-ins to be loaded by using the pollster-list option:

$ ceilometer-polling --polling-namespaces central \
        --pollster-list image image.size storage.*

Note

HA deployment is NOT supported if the pollster-list option is used.

Note

The ceilometer-polling service is available since Kilo release.

Central agent

This agent is responsible for polling public REST APIs to retrieve additional information on OpenStack resources not already surfaced via notifications, and also for polling hardware resources over SNMP.

The following services can be polled with this agent:

• OpenStack Networking
• OpenStack Object Storage
• OpenStack Block Storage
• Hardware resources via SNMP
• Energy consumption meters via Kwapi framework

To install and configure this service use the Install the Telemetry module section in the OpenStack Installation Guide.

The central agent does not need direct database connection. The samples collected by this agent are sent via AMQP to the notification agent to be processed.

Note

Prior to the Liberty release, data from the polling agents was processed locally and published accordingly rather than by the notification agent.

Compute agent

This agent is responsible for collecting resource usage data of VM instances on individual compute nodes within an OpenStack deployment. This mechanism requires a closer interaction with the hypervisor, therefore a separate agent type fulfills the collection of the related meters, which is placed on the host machines to locally retrieve this information.

A compute agent instance has to be installed on each and every compute node, installation instructions can be found in the Install the Compute agent for Telemetry section in the OpenStack Installation Guide.

Just like the central agent, this component also does not need a direct database connection. The samples are sent via AMQP to the notification agent.

The list of supported hypervisors can be found in telemetry-supported-hypervisors. The compute agent uses the API of the hypervisor installed on the compute hosts. Therefore the supported meters may be different in case of each virtualization back end, as each inspection tool provides a different set of meters.

The list of collected meters can be found in telemetry-compute-meters. The support column provides the information that which meter is available for each hypervisor supported by the Telemetry module.

Note

Telemetry supports Libvirt, which hides the hypervisor under it.

IPMI agent

This agent is responsible for collecting IPMI sensor data and Intel Node Manager data on individual compute nodes within an OpenStack deployment. This agent requires an IPMI capable node with the ipmitool utility installed, which is commonly used for IPMI control on various Linux distributions.

An IPMI agent instance could be installed on each and every compute node with IPMI support, except when the node is managed by the Bare metal service and the conductor.send_sensor_data option is set to true in the Bare metal service. It is no harm to install this agent on a compute node without IPMI or Intel Node Manager support, as the agent checks for the hardware and if none is available, returns empty data. It is suggested that you install the IPMI agent only on an IPMI capable node for performance reasons.

Just like the central agent, this component also does not need direct database access. The samples are sent via AMQP to the notification agent.

The list of collected meters can be found in telemetry-bare-metal-service.

Note

Do not deploy both the IPMI agent and the Bare metal service on one compute node. If conductor.send_sensor_data is set, this misconfiguration causes duplicated IPMI sensor samples.

Support for HA deployment

Both the polling agents and notification agents can run in an HA deployment, which means that multiple instances of these services can run in parallel with workload partitioning among these running instances.

The Tooz library provides the coordination within the groups of service instances. It provides an API above several back ends that can be used for building distributed applications.

Tooz supports various drivers including the following back end solutions:

• Zookeeper. Recommended solution by the Tooz project.
• Redis. Recommended solution by the Tooz project.
• Memcached. Recommended for testing.

You must configure a supported Tooz driver for the HA deployment of the Telemetry services.

For information about the required configuration options that have to be set in the ceilometer.conf configuration file for both the central and compute agents, see the Coordination section in the OpenStack Configuration Reference.

Notification agent HA deployment

In the Kilo release, workload partitioning support was added to the notification agent. This is particularly useful as the pipeline processing is handled exclusively by the notification agent now which may result in a larger amount of load.

To enable workload partitioning by notification agent, the backend_url option must be set in the ceilometer.conf configuration file. Additionally, workload_partitioning should be enabled in the Notification section in the OpenStack Configuration Reference.

Note

In Liberty, the notification agent creates multiple queues to divide the workload across all active agents. The number of queues can be controled by the pipeline_processing_queues option in the ceilometer.conf configuration file. A larger value will result in better distribution of tasks but will also require more memory and longer startup time. It is recommended to have a value approximately three times the number of active notification agents. At a minimum, the value should be equal to the number of active agents.

Polling agent HA deployment

Note

Without the backend_url option being set only one instance of both the central and compute agent service is able to run and function correctly.

The availability check of the instances is provided by heartbeat messages. When the connection with an instance is lost, the workload will be reassigned within the remained instances in the next polling cycle.

Note

Memcached uses a timeout value, which should always be set to a value that is higher than the heartbeat value set for Telemetry.

For backward compatibility and supporting existing deployments, the central agent configuration also supports using different configuration files for groups of service instances of this type that are running in parallel. For enabling this configuration set a value for the partitioning_group_prefix option in the Central section in the OpenStack Configuration Reference.

Warning

For each sub-group of the central agent pool with the same partitioning_group_prefix a disjoint subset of meters must be polled, otherwise samples may be missing or duplicated. The list of meters to poll can be set in the /etc/ceilometer/pipeline.yaml configuration file. For more information about pipelines see data-collection-and-processing.

To enable the compute agent to run multiple instances simultaneously with workload partitioning, the workload_partitioning option has to be set to True under the Compute section in the ceilometer.conf configuration file.

Send samples to Telemetry

While most parts of the data collection in the Telemetry module are automated, Telemetry provides the possibility to submit samples via the REST API to allow users to send custom samples into this module.

This option makes it possible to send any kind of samples without the need of writing extra code lines or making configuration changes.

The samples that can be sent to Telemetry are not limited to the actual existing meters. There is a possibility to provide data for any new, customer defined counter by filling out all the required fields of the POST request.

If the sample corresponds to an existing meter, then the fields like meter-type and meter name should be matched accordingly.

The required fields for sending a sample using the command line client are:

• ID of the corresponding resource. (--resource-id)

• Name of meter. (--meter-name)

• Type of meter. (--meter-type)

  Predefined meter types:

  • Gauge
  • Delta
  • Cumulative

• Unit of meter. (--meter-unit)

• Volume of sample. (--sample-volume)

To send samples to Telemetry using the command line client, the following command should be invoked:

$ ceilometer sample-create -r 37128ad6-daaa-4d22-9509-b7e1c6b08697 \
  -m memory.usage --meter-type gauge --meter-unit MB --sample-volume 48
+-------------------+--------------------------------------------+
| Property          | Value                                      |
+-------------------+--------------------------------------------+
| message_id        | 6118820c-2137-11e4-a429-08002715c7fb       |
| name              | memory.usage                               |
| project_id        | e34eaa91d52a4402b4cb8bc9bbd308c1           |
| resource_id       | 37128ad6-daaa-4d22-9509-b7e1c6b08697       |
| resource_metadata | {}                                         |
| source            | e34eaa91d52a4402b4cb8bc9bbd308c1:openstack |
| timestamp         | 2014-08-11T09:10:46.358926                 |
| type              | gauge                                      |
| unit              | MB                                         |
| user_id           | 679b0499e7a34ccb9d90b64208401f8e           |
| volume            | 48.0                                       |
+-------------------+--------------------------------------------+

Data collection and processing

The mechanism by which data is collected and processed is called a pipeline. Pipelines, at the configuration level, describe a coupling between sources of data and the corresponding sinks for transformation and publication of data.

A source is a producer of data: samples or events. In effect, it is a set of pollsters or notification handlers emitting datapoints for a set of matching meters and event types.

Each source configuration encapsulates name matching, polling interval determination, optional resource enumeration or discovery, and mapping to one or more sinks for publication.

Data gathered can be used for different purposes, which can impact how frequently it needs to be published. Typically, a meter published for billing purposes needs to be updated every 30 minutes while the same meter may be needed for performance tuning every minute.

Warning

Rapid polling cadences should be avoided, as it results in a huge amount of data in a short time frame, which may negatively affect the performance of both Telemetry and the underlying database back end. We therefore strongly recommend you do not use small granularity values like 10 seconds.

A sink, on the other hand, is a consumer of data, providing logic for the transformation and publication of data emitted from related sources.

In effect, a sink describes a chain of handlers. The chain starts with zero or more transformers and ends with one or more publishers. The first transformer in the chain is passed data from the corresponding source, takes some action such as deriving rate of change, performing unit conversion, or aggregating, before passing the modified data to the next step that is described in telemetry-publishers.

Pipeline configuration

Pipeline configuration by default, is stored in separate configuration files, called pipeline.yaml and event_pipeline.yaml, next to the ceilometer.conf file. The meter pipeline and event pipeline configuration files can be set by the pipeline_cfg_file and event_pipeline_cfg_file options listed in the Description of configuration options for api table section in the OpenStack Configuration Reference respectively. Multiple pipelines can be defined in one pipeline configuration file.

The meter pipeline definition looks like the following:

---
sources:
  - name: 'source name'
    interval: 'how often should the samples be injected into the pipeline'
    meters:
      - 'meter filter'
    resources:
      - 'list of resource URLs'
    sinks
      - 'sink name'
sinks:
  - name: 'sink name'
    transformers: 'definition of transformers'
    publishers:
      - 'list of publishers'

The interval parameter in the sources section should be defined in seconds. It determines the polling cadence of sample injection into the pipeline, where samples are produced under the direct control of an agent.

There are several ways to define the list of meters for a pipeline source. The list of valid meters can be found in telemetry-measurements. There is a possibility to define all the meters, or just included or excluded meters, with which a source should operate:

• To include all meters, use the * wildcard symbol. It is highly advisable to select only the meters that you intend on using to avoid flooding the metering database with unused data.
• To define the list of meters, use either of the following:
  • To define the list of included meters, use the meter_name syntax.
  • To define the list of excluded meters, use the !meter_name syntax.
  • For meters, which have variants identified by a complex name field, use the wildcard symbol to select all, e.g. for "instance:m1.tiny", use "instance:*".

Note

Please be aware that we do not have any duplication check between pipelines and if you add a meter to multiple pipelines then it is assumed the duplication is intentional and may be stored multiple times according to the specified sinks.

The above definition methods can be used in the following combinations:

• Use only the wildcard symbol.
• Use the list of included meters.
• Use the list of excluded meters.
• Use wildcard symbol with the list of excluded meters.

Note

At least one of the above variations should be included in the meters section. Included and excluded meters cannot co-exist in the same pipeline. Wildcard and included meters cannot co-exist in the same pipeline definition section.

The optional resources section of a pipeline source allows a static list of resource URLs to be configured for polling.

The transformers section of a pipeline sink provides the possibility to add a list of transformer definitions. The available transformers are:

Name of transformer	Reference name for configuration
Accumulator	accumulator
Aggregator	aggregator
Arithmetic	arithmetic
Rate of change	rate_of_change
Unit conversion	unit_conversion
Delta	delta

The publishers section contains the list of publishers, where the samples data should be sent after the possible transformations.

Similarly, the event pipeline definition looks like the following:

---
sources:
  - name: 'source name'
    events:
      - 'event filter'
    sinks
      - 'sink name'
sinks:
  - name: 'sink name'
    publishers:
      - 'list of publishers'

The event filter uses the same filtering logic as the meter pipeline.

Transformers

The definition of transformers can contain the following fields:

name

Name of the transformer.

parameters

Parameters of the transformer.

The parameters section can contain transformer specific fields, like source and target fields with different subfields in case of the rate of change, which depends on the implementation of the transformer.

In the case of the transformer that creates the cpu_util meter, the definition looks like the following:

transformers:
    - name: "rate_of_change"
      parameters:
          target:
              name: "cpu_util"
              unit: "%"
              type: "gauge"
              scale: "100.0 / (10**9 * (resource_metadata.cpu_number or 1))"

The rate of change the transformer generates is the cpu_util meter from the sample values of the cpu counter, which represents cumulative CPU time in nanoseconds. The transformer definition above defines a scale factor (for nanoseconds and multiple CPUs), which is applied before the transformation derives a sequence of gauge samples with unit '%', from sequential values of the cpu meter.

The definition for the disk I/O rate, which is also generated by the rate of change transformer:

transformers:
    - name: "rate_of_change"
      parameters:
          source:
              map_from:
                  name: "disk\\.(read|write)\\.(bytes|requests)"
                  unit: "(B|request)"
          target:
              map_to:
                  name: "disk.\\1.\\2.rate"
                  unit: "\\1/s"
              type: "gauge"

Unit conversion transformer

Transformer to apply a unit conversion. It takes the volume of the meter and multiplies it with the given scale expression. Also supports map_from and map_to like the rate of change transformer.

Sample configuration:

transformers:
    - name: "unit_conversion"
      parameters:
          target:
              name: "disk.kilobytes"
              unit: "KB"
              scale: "1.0 / 1024.0"

With map_from and map_to :

transformers:
    - name: "unit_conversion"
      parameters:
          source:
              map_from:
                  name: "disk\\.(read|write)\\.bytes"
          target:
              map_to:
                  name: "disk.\\1.kilobytes"
              scale: "1.0 / 1024.0"
              unit: "KB"

Aggregator transformer

A transformer that sums up the incoming samples until enough samples have come in or a timeout has been reached.

Timeout can be specified with the retention_time option. If we want to flush the aggregation after a set number of samples have been aggregated, we can specify the size parameter.

The volume of the created sample is the sum of the volumes of samples that came into the transformer. Samples can be aggregated by the attributes project_id, user_id and resource_metadata. To aggregate by the chosen attributes, specify them in the configuration and set which value of the attribute to take for the new sample (first to take the first sample's attribute, last to take the last sample's attribute, and drop to discard the attribute).

To aggregate 60s worth of samples by resource_metadata and keep the resource_metadata of the latest received sample:

transformers:
    - name: "aggregator"
      parameters:
          retention_time: 60
          resource_metadata: last

To aggregate each 15 samples by user_id and resource_metadata and keep the user_id of the first received sample and drop the resource_metadata:

transformers:
    - name: "aggregator"
      parameters:
          size: 15
          user_id: first
          resource_metadata: drop

Accumulator transformer

This transformer simply caches the samples until enough samples have arrived and then flushes them all down the pipeline at once:

transformers:
    - name: "accumulator"
      parameters:
          size: 15

Muli meter arithmetic transformer

This transformer enables us to perform arithmetic calculations over one or more meters and/or their metadata, for example:

memory_util = 100 * memory.usage / memory

A new sample is created with the properties described in the target section of the transformer's configuration. The sample's volume is the result of the provided expression. The calculation is performed on samples from the same resource.

Note

The calculation is limited to meters with the same interval.

Example configuration:

transformers:
    - name: "arithmetic"
      parameters:
        target:
          name: "memory_util"
          unit: "%"
          type: "gauge"
          expr: "100 * $(memory.usage) / $(memory)"

To demonstrate the use of metadata, here is the implementation of a silly meter that shows average CPU time per core:

transformers:
    - name: "arithmetic"
      parameters:
        target:
          name: "avg_cpu_per_core"
          unit: "ns"
          type: "cumulative"
          expr: "$(cpu) / ($(cpu).resource_metadata.cpu_number or 1)"

Note

Expression evaluation gracefully handles NaNs and exceptions. In such a case it does not create a new sample but only logs a warning.

Delta transformer

This transformer calculates the change between two sample datapoints of a resource. It can be configured to capture only the positive growth deltas.

Example configuration:

transformers:
    - name: "delta"
      parameters:
        target:
            name: "cpu.delta"
        growth_only: True

Meter definitions

The Telemetry module collects a subset of the meters by filtering notifications emitted by other OpenStack services. Starting with the Liberty release, you can find the meter definitions in a separate configuration file, called ceilometer/meter/data/meter.yaml. This enables operators/administrators to add new meters to Telemetry project by updating the meter.yaml file without any need for additional code changes.

Note

The meter.yaml file should be modified with care. Unless intended do not remove any existing meter definitions from the file. Also, the collected meters can differ in some cases from what is referenced in the documentation.

A standard meter definition looks like the following:

---
metric:
  - name: 'meter name'
    event_type: 'event name'
    type: 'type of meter eg: gauge, cumulative or delta'
    unit: 'name of unit eg: MB'
    volume: 'path to a measurable value eg: $.payload.size'
    resource_id: 'path to resouce id eg: $.payload.id'
    project_id: 'path to project id eg: $.payload.owner'

The definition above shows a simple meter definition with some fields, from which name, event_type, type, unit, and volume are required. If there is a match on the event type, samples are generated for the meter.

If you take a look at the meter.yaml file, it contains the sample definitions for all the meters that Telemetry is collecting from notifications. The value of each field is specified by using json path in order to find the right value from the notification message. In order to be able to specify the right field you need to be aware of the format of the consumed notification. The values that need to be searched in the notification message are set with a json path starting with $. For instance, if you need the size information from the payload you can define it like $.payload.size.

A notification message may contain multiple meters. You can use * in the meter definition to capture all the meters and generate samples respectively. You can use wild cards as shown in the following example:

---
metric:
  - name: $.payload.measurements.[*].metric.[*].name
    event_type: 'event_name.*'
    type: 'delta'
    unit: $.payload.measurements.[*].metric.[*].unit
    volume: payload.measurements.[*].result
    resource_id: $.payload.target
    user_id: $.payload.initiator.id
    project_id: $.payload.initiator.project_id

In the above example, the name field is a json path with matching a list of meter names defined in the notification message.

You can even use complex operations on json paths. In the following example, volume and resource_id fields perform an arithmetic and string concatenation:

---
metric:
- name: 'compute.node.cpu.idle.percent'
  event_type: 'compute.metrics.update'
  type: 'gauge'
  unit: 'percent'
  volume: payload.metrics[?(@.name='cpu.idle.percent')].value * 100
  resource_id: $.payload.host + "_" + $.payload.nodename

You will find some existence meters in the meter.yaml. These meters have a volume as 1 and are at the bottom of the yaml file with a note suggesting that these will be removed in Mitaka release.

For example, the meter definition for existence meters is as follows:

---
metric:
  - name: 'meter name'
    type: 'delta'
    unit: 'volume'
    volume: 1
    event_type:
        - 'event type'
    resource_id: $.payload.volume_id
    user_id: $.payload.user_id
    project_id: $.payload.tenant_id

These meters are not loaded by default. To load these meters, flip the disable_non_metric_meters option in the ceilometer.conf file.

Block Storage audit script setup to get notifications

If you want to collect OpenStack Block Storage notification on demand, you can use cinder-volume-usage-audit from OpenStack Block Storage. This script becomes available when you install OpenStack Block Storage, so you can use it without any specific settings and you don't need to authenticate to access the data. To use it, you must run this command in the following format:

$ cinder-volume-usage-audit \
  --start_time='YYYY-MM-DD HH:MM:SS' --end_time='YYYY-MM-DD HH:MM:SS' --send_actions

This script outputs what volumes or snapshots were created, deleted, or exists in a given period of time and some information about these volumes or snapshots. Information about the existence and size of volumes and snapshots is store in the Telemetry module. This data is also stored as an event which is the recommended usage as it provides better indexing of data.

Using this script via cron you can get notifications periodically, for example, every 5 minutes:

*/5 * * * * /path/to/cinder-volume-usage-audit --send_actions

Storing samples

The Telemetry module has a separate service that is responsible for persisting the data that comes from the pollsters or is received as notifications. The data can be stored in a file or a database back end, for which the list of supported databases can be found in telemetry-supported-databases. The data can also be sent to an external data store by using an HTTP dispatcher.

The ceilometer-collector service receives the data as messages from the message bus of the configured AMQP service. It sends these datapoints without any modification to the configured target. The service has to run on a host machine from which it has access to the configured dispatcher.

Note

Multiple dispatchers can be configured for Telemetry at one time.

Multiple ceilometer-collector processes can be run at a time. It is also supported to start multiple worker threads per collector process. The collector_workers configuration option has to be modified in the Collector section of the ceilometer.conf configuration file.

Note

Prior to the Juno release, it is not recommended to use multiple workers per collector process when using PostgreSQL as the database back end.

Database dispatcher

When the database dispatcher is configured as data store, you have the option to set a time_to_live option (ttl) for samples. By default the time to live value for samples is set to -1, which means that they are kept in the database forever.

The time to live value is specified in seconds. Each sample has a time stamp, and the ttl value indicates that a sample will be deleted from the database when the number of seconds has elapsed since that sample reading was stamped. For example, if the time to live is set to 600, all samples older than 600 seconds will be purged from the database.

Certain databases support native TTL expiration. In cases where this is not possible, a command-line script, which you can use for this purpose is ceilometer-expirer. You can run it in a cron job, which helps to keep your database in a consistent state.

The level of support differs in case of the configured back end:

Database	TTL value support	Note
MongoDB	Yes	MongoDB has native TTL support for deleting samples that are older than the configured ttl value.
SQL-based back ends	Yes	ceilometer-expirer has to be used for deleting samples and its related data from the database.
HBase	No	Telemetry's HBase support does not include native TTL nor ceilometer-expirer support.
DB2 NoSQL	No	DB2 NoSQL does not have native TTL nor ceilometer-expirer support.

HTTP dispatcher

The Telemetry module supports sending samples to an external HTTP target. The samples are sent without any modification. To set this option as the collector's target, the dispatcher has to be changed to http in the ceilometer.conf configuration file. For the list of options that you need to set, see the see the dispatcher_http section in the OpenStack Configuration Reference.

File dispatcher

You can store samples in a file by setting the dispatcher option in the ceilometer.conf file. For the list of configuration options, see the dispatcher_file section in the OpenStack Configuration Reference.

Gnocchi dispatcher

The Telemetry module supports sending the metering data to Gnocchi back end through the gnocchi dispatcher. To set this option as the target, change the dispatcher to gnocchi in the ceilometer.conf configuration file.

For the list of options that you need to set, see the dispatcher_gnocchi section in the OpenStack Configuration Reference.