Expose Prometheus#histogramFlavor property

Closes gh-20853

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/prometheus/PrometheusProperties.java

 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,8 @@ import java.time.Duration;
 import java.util.HashMap;
 import java.util.Map;
 
+import io.micrometer.prometheus.HistogramFlavor;
+
 import org.springframework.boot.actuate.metrics.export.prometheus.PrometheusPushGatewayManager.ShutdownOperation;
 import org.springframework.boot.context.properties.ConfigurationProperties;
 
@@ -46,6 +48,11 @@ public class PrometheusProperties {
 	 */
 	private final Pushgateway pushgateway = new Pushgateway();
 
+	/**
+	 * Histogram type for backing DistributionSummary and Timer.
+	 */
+	private HistogramFlavor histogramFlavor = HistogramFlavor.Prometheus;
+
 	/**
 	 * Step size (i.e. reporting frequency) to use.
 	 */
@@ -59,6 +66,14 @@ public class PrometheusProperties {
 		this.descriptions = descriptions;
 	}
 
+	public HistogramFlavor getHistogramFlavor() {
+		return this.histogramFlavor;
+	}
+
+	public void setHistogramFlavor(HistogramFlavor histogramFlavor) {
+		this.histogramFlavor = histogramFlavor;
+	}
+
 	public Duration getStep() {
 		return this.step;
 	}

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/prometheus/PrometheusPropertiesConfigAdapter.java

 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@ package org.springframework.boot.actuate.autoconfigure.metrics.export.prometheus
 
 import java.time.Duration;
 
+import io.micrometer.prometheus.HistogramFlavor;
 import io.micrometer.prometheus.PrometheusConfig;
 
 import org.springframework.boot.actuate.autoconfigure.metrics.export.properties.PropertiesConfigAdapter;
@@ -45,6 +46,11 @@ class PrometheusPropertiesConfigAdapter extends PropertiesConfigAdapter<Promethe
 		return get(PrometheusProperties::isDescriptions, PrometheusConfig.super::descriptions);
 	}
 
+	@Override
+	public HistogramFlavor histogramFlavor() {
+		return get(PrometheusProperties::getHistogramFlavor, PrometheusConfig.super::histogramFlavor);
+	}
+
 	@Override
 	public Duration step() {
 		return get(PrometheusProperties::getStep, PrometheusConfig.super::step);

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -328,6 +328,10 @@
       "description": "Whether exporting of metrics to Prometheus is enabled.",
       "defaultValue": true
     },
+    {
+      "name": "management.metrics.export.prometheus.histogram-flavor",
+      "defaultValue": "prometheus"
+    },
     {
       "name": "management.metrics.export.signalfx.num-threads",
       "type": "java.lang.Integer",

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/export/prometheus/PrometheusPropertiesTests.java

 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -33,6 +33,7 @@ class PrometheusPropertiesTests {
 		PrometheusProperties properties = new PrometheusProperties();
 		PrometheusConfig config = PrometheusConfig.DEFAULT;
 		assertThat(properties.isDescriptions()).isEqualTo(config.descriptions());
+		assertThat(properties.getHistogramFlavor()).isEqualTo(config.histogramFlavor());
 		assertThat(properties.getStep()).isEqualTo(config.step());
 	}