Instrumenting for metrics

Metrics are measurements at a given moment of a particular aspect of an application during runtime. An individual capture is called a metric event and consists of a timestamp, a measurement, and associated metadata. Metric events are used to provide an aggregated view of the behavior of an application at runtime. For example, a metric event can be a counter incremented by 1 when a request is handled by a service. The individual event is not especially useful. However, when aggregated into a sum of requests over a period of time, you can see how many requests are made to a service over that period of time.

The OpenTelemetry API does not allow for custom aggregations but does provide some common aggregations, such as sum, count, last value, and histograms, which are supported by backend visualization and analysis software such as Prometheus.

To give you a better idea of when metrics are useful, here are some example scenarios:

• Providing the aggregate...