add _total suffixes to prometheus counters (#3360)

CHANGELOG.md

@@ -21,6 +21,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - The `"go.opentelemetry.io/otel/exporters/prometheus".New` now also returns an error indicating the failure to register the exporter with Prometheus. (#3239)
 - The prometheus exporter will no longer try to enumerate the metrics it will send to prometheus on startup.
    This fixes the `reader is not registered` warning currently emitted on startup. (#3291 #3342)
+- The `go.opentelemetry.io/otel/exporters/prometheus` exporter now correctly adds _total suffixes to counter metrics. (#3360)
 
 ### Fixed
 

exporters/prometheus/exporter.go

@@ -54,6 +54,10 @@ type collector struct {
 	createTargetInfoOnce sync.Once
 }
 
+// prometheus counters MUST have a _total suffix:
+// https://github.com/open-telemetry/opentelemetry-specification/blob/v1.14.0/specification/metrics/data-model.md#sums-1
+const counterSuffix = "_total"
+
 // New returns a Prometheus Exporter.
 func New(opts ...Option) (*Exporter, error) {
 	cfg := newConfig(opts...)
@@ -197,8 +201,12 @@ func getSumMetricData[N int64 | float64](sum metricdata.Sum[N], m metricdata.Met
 	}
 	dataPoints := make([]*metricData, 0, len(sum.DataPoints))
 	for _, dp := range sum.DataPoints {
+		name := sanitizeName(m.Name)
+		if sum.IsMonotonic {
+			name += counterSuffix
+		}
 		keys, values := getAttrs(dp.Attributes)
-		desc := prometheus.NewDesc(sanitizeName(m.Name), m.Description, keys, nil)
+		desc := prometheus.NewDesc(name, m.Description, keys, nil)
 		md := &metricData{
 			name:            m.Name,
 			description:     desc,

exporters/prometheus/testdata/counter.txt

@@ -1,6 +1,6 @@
-# HELP foo a simple counter
-# TYPE foo counter
-foo{A="B",C="D",E="true",F="42"} 24.3
+# HELP foo_total a simple counter
+# TYPE foo_total counter
+foo_total{A="B",C="D",E="true",F="42"} 24.3
 # HELP target_info Target metadata
 # TYPE target_info gauge
 target_info{service_name="prometheus_test",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="latest"} 1

exporters/prometheus/testdata/custom_resource.txt

@@ -1,6 +1,6 @@
-# HELP foo a simple counter
-# TYPE foo counter
-foo{A="B",C="D",E="true",F="42"} 24.3
+# HELP foo_total a simple counter
+# TYPE foo_total counter
+foo_total{A="B",C="D",E="true",F="42"} 24.3
 # HELP target_info Target metadata
 # TYPE target_info gauge
 target_info{A="B",C="D",service_name="prometheus_test",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="latest"} 1

exporters/prometheus/testdata/empty_resource.txt

@@ -1,6 +1,6 @@
-# HELP foo a simple counter
-# TYPE foo counter
-foo{A="B",C="D",E="true",F="42"} 24.3
+# HELP foo_total a simple counter
+# TYPE foo_total counter
+foo_total{A="B",C="D",E="true",F="42"} 24.3
 # HELP target_info Target metadata
 # TYPE target_info gauge
 target_info 1

exporters/prometheus/testdata/sanitized_labels.txt

@@ -1,6 +1,7 @@
-# HELP foo a sanitary counter
-# TYPE foo counter
-foo{A_B="Q",C_D="Y;Z"} 24.3
+# HELP foo_total a sanitary counter
+# TYPE foo_total counter
+foo_total{A_B="Q",C_D="Y;Z"} 24.3
 # HELP target_info Target metadata
 # TYPE target_info gauge
 target_info{service_name="prometheus_test",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="latest"} 1
+

exporters/prometheus/testdata/sanitized_names.txt

@@ -1,9 +1,9 @@
 # HELP bar a fun little gauge
 # TYPE bar gauge
 bar{A="B",C="D"} 75
-# HELP _0invalid_counter_name a counter with an invalid name
-# TYPE _0invalid_counter_name counter
-_0invalid_counter_name{A="B",C="D"} 100
+# HELP _0invalid_counter_name_total a counter with an invalid name
+# TYPE _0invalid_counter_name_total counter
+_0invalid_counter_name_total{A="B",C="D"} 100
 # HELP invalid_gauge_name a gauge with an invalid name
 # TYPE invalid_gauge_name gauge
 invalid_gauge_name{A="B",C="D"} 100

exporters/prometheus/testdata/without_target_info.txt

@@ -1,3 +1,3 @@
-# HELP foo a simple counter
-# TYPE foo counter
-foo{A="B",C="D",E="true",F="42"} 24.3
+# HELP foo_total a simple counter
+# TYPE foo_total counter
+foo_total{A="B",C="D",E="true",F="42"} 24.3