Modify Prometheus exporter to translate non-monotonic Sums into gauges

Add unit tests for translating monotonic and non-monotonic Sums to prometheus metrics

Update prometheus metric translation to match spec

Added a check for the aggregation temporality of a Sum.
"If the aggregation temporality is cumulative and the sum is non-monotonic, it MUST be converted to a Prometheus Gauge."

Update changelog

Author: brettimus

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+- Modify Prometheus exporter to translate non-monotonic Sums into Gauges
+  ([#3306](https://github.com/open-telemetry/opentelemetry-python/pull/3306))
 - Select histogram aggregation with an environment variable
   ([#3265](https://github.com/open-telemetry/opentelemetry-python/pull/3265))
 - Move Protobuf encoding to its own package
@@ -41,7 +43,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Version 1.16.0/0.37b0 (2023-02-17)
 
-- Change ``__all__`` to be statically defined.
+- Change `__all__` to be statically defined.
   ([#3143](https://github.com/open-telemetry/opentelemetry-python/pull/3143))
 - Remove the ability to set a global metric prefix for Prometheus exporter
   ([#3137](https://github.com/open-telemetry/opentelemetry-python/pull/3137))
@@ -64,7 +66,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Create a single resource instance
   ([#3118](https://github.com/open-telemetry/opentelemetry-python/pull/3118))
 
-
 ## Version 1.15.0/0.36b0 (2022-12-09)
 
 - PeriodicExportingMetricsReader with +Inf interval
@@ -82,7 +83,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#3027](https://github.com/open-telemetry/opentelemetry-python/pull/3027))
 - Update logging to include logging api as per specification
   ([#3038](https://github.com/open-telemetry/opentelemetry-python/pull/3038))
-- Fix: Avoid generator in metrics _ViewInstrumentMatch.collect()
+- Fix: Avoid generator in metrics \_ViewInstrumentMatch.collect()
   ([#3035](https://github.com/open-telemetry/opentelemetry-python/pull/3035)
 - [exporter-otlp-proto-grpc] add user agent string
   ([#3009](https://github.com/open-telemetry/opentelemetry-python/pull/3009))

exporter/opentelemetry-exporter-prometheus/src/opentelemetry/exporter/prometheus/__init__.py

@@ -244,7 +244,13 @@ def _translate_to_prometheus(
             for pre_metric_family_id, label_values, value in zip(
                 pre_metric_family_ids, label_valuess, values
             ):
-                if isinstance(metric.data, Sum):
+                is_non_monotonic_sum = isinstance(metric.data, Sum) and metric.data.is_monotonic == False
+                is_cumulative = isinstance(metric.data, Sum) and metric.data.aggregation_temporality == AggregationTemporality.CUMULATIVE
+
+                # The prometheus compatibility spec for sums says: If the aggregation temporality is cumulative and the sum is non-monotonic, it MUST be converted to a Prometheus Gauge.
+                should_convert_sum_to_gauge = (is_non_monotonic_sum and is_cumulative)
+
+                if isinstance(metric.data, Sum) and not should_convert_sum_to_gauge:
 
                     metric_family_id = "|".join(
                         [pre_metric_family_id, CounterMetricFamily.__name__]
@@ -262,7 +268,7 @@ def _translate_to_prometheus(
                     metric_family_id_metric_family[
                         metric_family_id
                     ].add_metric(labels=label_values, value=value)
-                elif isinstance(metric.data, Gauge):
+                elif isinstance(metric.data, Gauge) or should_convert_sum_to_gauge:
 
                     metric_family_id = "|".join(
                         [pre_metric_family_id, GaugeMetricFamily.__name__]

exporter/opentelemetry-exporter-prometheus/tests/test_prometheus_exporter.py

@@ -120,7 +120,7 @@ def test_histogram_to_prometheus(self):
             ),
         )
 
-    def test_sum_to_prometheus(self):
+    def test_monotonic_sum_to_prometheus(self):
         labels = {"environment@": "staging", "os": "Windows"}
         metric = _generate_sum(
             "test@sum",
@@ -163,6 +163,50 @@ def test_sum_to_prometheus(self):
                 prometheus_metric.samples[0].labels["os"], "Windows"
             )
 
+    def test_non_monotonic_sum_to_prometheus(self):
+        labels = {"environment@": "staging", "os": "Windows"}
+        metric = _generate_sum(
+            "test@sum",
+            123,
+            attributes=labels,
+            description="testdesc",
+            unit="testunit",
+            is_monotonic=False
+        )
+
+        metrics_data = MetricsData(
+            resource_metrics=[
+                ResourceMetrics(
+                    resource=Mock(),
+                    scope_metrics=[
+                        ScopeMetrics(
+                            scope=Mock(),
+                            metrics=[metric],
+                            schema_url="schema_url",
+                        )
+                    ],
+                    schema_url="schema_url",
+                )
+            ]
+        )
+
+        collector = _CustomCollector()
+        collector.add_metrics_data(metrics_data)
+
+        for prometheus_metric in collector.collect():
+            self.assertEqual(type(prometheus_metric), GaugeMetricFamily)
+            self.assertEqual(prometheus_metric.name, "test_sum_testunit")
+            self.assertEqual(prometheus_metric.documentation, "testdesc")
+            self.assertTrue(len(prometheus_metric.samples) == 1)
+            self.assertEqual(prometheus_metric.samples[0].value, 123)
+            self.assertTrue(len(prometheus_metric.samples[0].labels) == 2)
+            self.assertEqual(
+                prometheus_metric.samples[0].labels["environment_"], "staging"
+            )
+            self.assertEqual(
+                prometheus_metric.samples[0].labels["os"], "Windows"
+            )
+
     def test_gauge_to_prometheus(self):
         labels = {"environment@": "dev", "os": "Unix"}
         metric = _generate_gauge(

tests/opentelemetry-test-utils/src/opentelemetry/test/metrictestutil.py

@@ -39,7 +39,7 @@ def _generate_metric(
 
 
 def _generate_sum(
-    name, value, attributes=None, description=None, unit=None
+    name, value, attributes=None, description=None, unit=None, is_monotonic=True
 ) -> Metric:
     if attributes is None:
         attributes = BoundedAttributes(attributes={"a": 1, "b": True})
@@ -55,7 +55,7 @@ def _generate_sum(
                 )
             ],
             aggregation_temporality=AggregationTemporality.CUMULATIVE,
-            is_monotonic=True,
+            is_monotonic=is_monotonic,
         ),
         description=description,
         unit=unit,