Data processing and pipelines

updated: 2020-05-29 08:30

Data processing and pipelines¶

The mechanism by which data is processed is called a pipeline. Pipelines, at the configuration level, describe a coupling between sources of data and the corresponding sinks for publication of data. This functionality is handled by the notification agents.

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

Each source configuration encapsulates name matching and mapping to one or more sinks for publication.

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

In effect, a sink describes a list of one or more publishers.

Pipeline configuration¶

The notification agent supports two pipelines: one that handles samples and another that handles events. The pipelines can be enabled and disabled by setting pipelines option in the [notifications] section.

The actual configuration of each pipelines is, by default, stored in separate configuration files: pipeline.yaml and event_pipeline.yaml. The location of the configuration files can be set by the pipeline_cfg_file and event_pipeline_cfg_file options listed in Ceilometer Configuration Options

The meter pipeline definition looks like:

---
sources:
  - name: 'source name'
    meters:
      - 'meter filter'
    sinks:
      - 'sink name'
sinks:
  - name: 'sink name'
    publishers:
      - 'list of publishers'

There are several ways to define the list of meters for a pipeline source. The list of valid meters can be found in 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.

Note

The OpenStack Telemetry service does 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 publishers section contains the list of publishers, where the samples data should be sent.

Similarly, the event pipeline definition looks like:

---
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.

Publishers¶

The Telemetry service provides several transport methods to transfer the data collected to an external system. The consumers of this data are widely different, like monitoring systems, for which data loss is acceptable and billing systems, which require reliable data transportation. Telemetry provides methods to fulfill the requirements of both kind of systems.

The publisher component makes it possible to save the data into persistent storage through the message bus or to send it to one or more external consumers. One chain can contain multiple publishers.

To solve this problem, the multi-publisher can be configured for each data point within the Telemetry service, allowing the same technical meter or event to be published multiple times to multiple destinations, each potentially using a different transport.

The following publisher types are supported:

gnocchi (default)¶

When the gnocchi publisher is enabled, measurement and resource information is pushed to gnocchi for time-series optimized storage. Gnocchi must be registered in the Identity service as Ceilometer discovers the exact path via the Identity service.

More details on how to enable and configure gnocchi can be found on its official documentation page.

prometheus¶

Metering data can be send to the pushgateway of Prometheus by using:

prometheus://pushgateway-host:9091/metrics/job/openstack-telemetry

With this publisher, timestamp are not sent to Prometheus due to Prometheus Pushgateway design. All timestamps are set at the time it scrapes the metrics from the Pushgateway and not when the metric was polled on the OpenStack services.

In order to get timeseries in Prometheus that looks like the reality (but with the lag added by the Prometheus scrapping mechanism). The scrape_interval for the pushgateway must be lower and a multiple of the Ceilometer polling interval.

You can read more here

Due to this, this is not recommended to use this publisher for billing purpose as timestamps in Prometheus will not be exact.

panko¶

Event data in Ceilometer can be stored in panko which provides an HTTP REST interface to query system events in OpenStack. To push data to panko, set the publisher to panko://.

notifier¶

The notifier publisher can be specified in the form of notifier://?option1=value1&option2=value2. It emits data over AMQP using oslo.messaging. Any consumer can then subscribe to the published topic for additional processing.

The following customization options are available:

per_meter_topic

The value of this parameter is 1. It is used for publishing the samples on additional metering_topic.sample_name topic queue besides the default metering_topic queue.

policy

Used for configuring the behavior for the case, when the publisher fails to send the samples, where the possible predefined values are:

default: Used for waiting and blocking until the samples have been sent.
drop: Used for dropping the samples which are failed to be sent.
queue: Used for creating an in-memory queue and retrying to send the samples on the queue in the next samples publishing period (the queue length can be configured with max_queue_length, where 1024 is the default value).

topic

The topic name of the queue to publish to. Setting this will override the default topic defined by metering_topic and event_topic options. This option can be used to support multiple consumers.

udp¶

This publisher can be specified in the form of udp://<host>:<port>/. It emits metering data over UDP.

file¶

The file publisher can be specified in the form of file://path?option1=value1&option2=value2. This publisher records metering data into a file.

Note

If a file name and location is not specified, the file publisher does not log any meters, instead it logs a warning message in the configured log file for Telemetry.

The following options are available for the file publisher:

max_bytes: When this option is greater than zero, it will cause a rollover. When the specified size is about to be exceeded, the file is closed and a new file is silently opened for output. If its value is zero, rollover never occurs.
backup_count: If this value is non-zero, an extension will be appended to the filename of the old log, as ‘.1’, ‘.2’, and so forth until the specified value is reached. The file that is written and contains the newest data is always the one that is specified without any extensions.

http¶

The Telemetry service supports sending samples to an external HTTP target. The samples are sent without any modification. To set this option as the notification agents’ target, set http:// as a publisher endpoint in the pipeline definition files. The HTTP target should be set along with the publisher declaration. For example, additional configuration options can be passed in: http://localhost:80/?option1=value1&option2=value2

The following options are available:

timeout: The number of seconds before HTTP request times out.
max_retries: The number of times to retry a request before failing.
batch: If false, the publisher will send each sample and event individually, whether or not the notification agent is configured to process in batches.
verify_ssl: If false, the ssl certificate verification is disabled.

The default publisher is gnocchi, without any additional options specified. A sample publishers section in the /etc/ceilometer/pipeline.yaml looks like the following:

publishers:
    - gnocchi://
    - panko://
    - udp://10.0.0.2:1234
    - notifier://?policy=drop&max_queue_length=512&topic=custom_target

updated: 2020-05-29 08:30

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