Datasources

Note

The Prometheus datasource is deprecated as of the 2026.1 release and will be removed in a future release. Use the Aetos datasource instead, which provides the same functionality with added multi-tenancy and Keystone authentication support. See the Migrating from Prometheus to Aetos guide.

• Aetos datasource
• Grafana datasource
• Migrating from Prometheus to Aetos
• Prometheus datasource

DataSource base class

All datasource backends inherit from DataSourceBase and share a common metric-retrieval interface.

Metric retrieval

statistic_aggregation(resource, resource_type, meter_name, period, aggregate, granularity) is the public method used by strategies to retrieve a metric value. It is implemented in the base class and manages a per-instance in-memory cache backed by MetricDataCache. The cache key encodes all five parameters: (resource.uuid, meter_name, aggregate, period, granularity). On the first call for a given combination of these five values, the result is fetched from the backend and stored in the cache. Subsequent calls with identical arguments return the cached value without contacting the backend again.

Each concrete datasource implements _statistic_aggregation with the same signature. That private method contains the backend-specific query logic and is called by the base class on a cache miss.

Cache injection

inject_metric(resource_uuid, metric, aggregation, period, value, granularity=300) writes a value directly into the cache without querying the backend. Any subsequent statistic_aggregation call with the same resource_uuid, metric, aggregation, period, and granularity will return the injected value.

Parameter	Description
resource_uuid	UUID of the resource
metric	Metric name as a key from METRIC_MAP
aggregation	Aggregation method (e.g. 'mean')
period	Time span in seconds the value covers
value	The metric value to store
granularity	Granularity in seconds (default 300)

Implementing a new datasource

A new datasource must:

• Inherit from DataSourceBase and call super().__init__() to initialise the metric cache.

• Override _statistic_aggregation with the backend-specific query logic.

• Override the remaining abstract methods defined in DataSourceBase (check_availability, list_metrics, statistic_series, and the get_host_* / get_instance_* convenience methods).

Warning

Overriding statistic_aggregation in a concrete datasource will bypass the base-class caching system. If you do so, the datasource becomes responsible for implementing its own caching strategy and must also provide its own inject_metric implementation so that callers can pre-populate the cache with externally computed values.