Metrics

Before you dive in to the metrics concepts outlined below, review these concepts in the official OpenTelemetry documentation, found here.

The ExportMetricServiceRequest

All OpenTelemetry collectors receive OTLP metrics from applications in the form of an ExportMetricServiceRequest. This is a well known message, and its structure can be found in the official opentelemetry-proto repository. The diagram below provides the general structure of this message (some properties omitted for brevity).

When the OpenTelemetry Collector exports metrics to an endpoint, it typically batches those metrics up and sends them by resource (eg. a microservice), hence the list of resources in an ExportMetricServiceRequest. Each ScopeMetrics will be associated with one resource, and the same goes for the Metrics that are associated with an instrumentation scope.

For each Metric, then, you know what instrumentation library was used to create the Metric, and you also know which Resource produced the Metric.

What Are Metrics?

The OpenTelemetry Metric consists of the name of the meter, an optional description and unit, and the kind of meter. The kinds of meters are:

• Sum
• Gauge
• Histogram
• ExponentialHistogram
• Summary

The available properties of a Metricthat can be queried are listed below:

message Where {
    oneof value {
        PropertyFilter property = 1;
        OrFilter or = 2;
        odddotnet.proto.common.v1.InstrumentationScopeFilter instrumentationScope = 3;
        odddotnet.proto.resource.v1.ResourceFilter resource = 4;
        odddotnet.proto.common.v1.StringProperty instrumentationScopeSchemaUrl = 5;
        odddotnet.proto.common.v1.StringProperty ResourceSchemaUrl = 6;
    }
}

message PropertyFilter {
    reserved 4, 6, 8;
    oneof value {
        odddotnet.proto.common.v1.StringProperty name = 1;
        odddotnet.proto.common.v1.StringProperty description = 2;
        odddotnet.proto.common.v1.StringProperty unit = 3;
        GaugeFilter gauge = 5;
        SumFilter sum = 7;
        HistogramFilter histogram = 9;
        ExponentialHistogramFilter exponentialHistogram = 10;
        SummaryFilter summary = 11;
        odddotnet.proto.common.v1.KeyValueProperty metadata = 12;
    }
}

The PropertyFilter includes a number of additional filters for the different meter types, such as the GaugeFilter for querying properties associated with the Gauge. See Metric Queries for more information around querying metrics.

The proto files for Metrics can be found here.