Exemplars

Exemplars can be added to counter and histogram metrics. Exemplars can be specified by passing a dict of label value pairs to be exposed as the exemplar. For example with a counter:

from prometheus_client import Counter
c = Counter('my_requests_total', 'HTTP Failures', ['method', 'endpoint'])
c.labels('get', '/').inc(exemplar={'trace_id': 'abc123'})
c.labels('post', '/submit').inc(1.0, {'trace_id': 'def456'})

And with a histogram:

from prometheus_client import Histogram
h = Histogram('request_latency_seconds', 'Description of histogram')
h.observe(4.7, {'trace_id': 'abc123'})

Exemplars are only rendered in the OpenMetrics exposition format. If using the HTTP server or apps in this library, content negotiation can be used to specify OpenMetrics (which is done by default in Prometheus). Otherwise it will be necessary to use generate_latest from prometheus_client.openmetrics.exposition to view exemplars.

To view exemplars in Prometheus it is also necessary to enable the the exemplar-storage feature flag:

--enable-feature=exemplar-storage

Additional information is available in the Prometheus documentation.