allow duplicate metric names

Author: jaydeluca

prometheus-metrics-config/src/main/java/io/prometheus/metrics/config/PrometheusProperties.java

@@ -21,6 +21,7 @@ public class PrometheusProperties {
   private final ExporterHttpServerProperties exporterHttpServerProperties;
   private final ExporterOpenTelemetryProperties exporterOpenTelemetryProperties;
   private final ExporterPushgatewayProperties exporterPushgatewayProperties;
+  private final RegistryProperties registryProperties;
 
   /**
    * Get the properties instance. When called for the first time, {@code get()} loads the properties
@@ -49,7 +50,8 @@ public PrometheusProperties(
       ExporterFilterProperties exporterFilterProperties,
       ExporterHttpServerProperties httpServerConfig,
       ExporterPushgatewayProperties pushgatewayProperties,
-      ExporterOpenTelemetryProperties otelConfig) {
+      ExporterOpenTelemetryProperties otelConfig,
+      RegistryProperties registryProperties) {
     this.defaultMetricsProperties = defaultMetricsProperties;
     this.metricProperties.putAll(metricProperties);
     this.exemplarProperties = exemplarProperties;
@@ -58,6 +60,7 @@ public PrometheusProperties(
     this.exporterHttpServerProperties = httpServerConfig;
     this.exporterPushgatewayProperties = pushgatewayProperties;
     this.exporterOpenTelemetryProperties = otelConfig;
+    this.registryProperties = registryProperties;
   }
 
   /**
@@ -102,6 +105,10 @@ public ExporterOpenTelemetryProperties getExporterOpenTelemetryProperties() {
     return exporterOpenTelemetryProperties;
   }
 
+  public RegistryProperties getRegistryProperties() {
+    return registryProperties;
+  }
+
   public static class Builder {
     private MetricsProperties defaultMetricsProperties = MetricsProperties.builder().build();
     private Map<String, MetricsProperties> metricProperties = new HashMap<>();
@@ -115,6 +122,7 @@ public static class Builder {
         ExporterPushgatewayProperties.builder().build();
     private ExporterOpenTelemetryProperties otelConfig =
         ExporterOpenTelemetryProperties.builder().build();
+    private RegistryProperties registryProperties = RegistryProperties.builder().build();
 
     private Builder() {}
 
@@ -166,6 +174,11 @@ public Builder exporterOpenTelemetryProperties(
       return this;
     }
 
+    public Builder registryProperties(RegistryProperties registryProperties) {
+      this.registryProperties = registryProperties;
+      return this;
+    }
+
     public PrometheusProperties build() {
       return new PrometheusProperties(
           defaultMetricsProperties,
@@ -175,7 +188,8 @@ public PrometheusProperties build() {
           exporterFilterProperties,
           exporterHttpServerProperties,
           pushgatewayProperties,
-          otelConfig);
+          otelConfig,
+          registryProperties);
     }
   }
 }

prometheus-metrics-config/src/main/java/io/prometheus/metrics/config/PrometheusPropertiesLoader.java

@@ -42,6 +42,7 @@ public static PrometheusProperties load(Map<Object, Object> externalProperties)
         ExporterPushgatewayProperties.load(properties);
     ExporterOpenTelemetryProperties exporterOpenTelemetryProperties =
         ExporterOpenTelemetryProperties.load(properties);
+    RegistryProperties registryProperties = RegistryProperties.load(properties);
     validateAllPropertiesProcessed(properties);
     return new PrometheusProperties(
         defaultMetricsProperties,
@@ -51,7 +52,8 @@ public static PrometheusProperties load(Map<Object, Object> externalProperties)
         exporterFilterProperties,
         exporterHttpServerProperties,
         exporterPushgatewayProperties,
-        exporterOpenTelemetryProperties);
+        exporterOpenTelemetryProperties,
+        registryProperties);
   }
 
   // This will remove entries from properties when they are processed.

prometheus-metrics-config/src/main/java/io/prometheus/metrics/config/RegistryProperties.java

@@ -0,0 +1,72 @@
+package io.prometheus.metrics.config;
+
+import java.util.Map;
+import javax.annotation.Nullable;
+
+/** Properties starting with io.prometheus.registry */
+public class RegistryProperties {
+
+  private static final String ALLOW_DUPLICATE_REGISTRATION = "allowDuplicateRegistration";
+  private static final String PREFIX = "io.prometheus.registry";
+
+  @Nullable private final Boolean allowDuplicateRegistration;
+
+  private RegistryProperties(@Nullable Boolean allowDuplicateRegistration) {
+    this.allowDuplicateRegistration = allowDuplicateRegistration;
+  }
+
+  /**
+   * If true, allows registering multiple collectors with the same metric name but potentially
+   * different label sets. Default is false for backward compatibility.
+   *
+   * <p>When enabled, metrics with the same name but different labels can coexist, which is useful
+   * for integration with frameworks like Micrometer that may create multiple collectors for the
+   * same metric with varying label sets.
+   *
+   * <p>Note: Registering metrics with the same name AND the same label set may produce confusing
+   * results in Prometheus queries, as multiple time series with identical labels will be present.
+   *
+   * <p>This property only affects registries created with {@code new
+   * PrometheusRegistry(allowDuplicateRegistration)}. The static {@code
+   * PrometheusRegistry.defaultRegistry} always uses the default value (false).
+   *
+   * <p>Property: {@code io.prometheus.registry.allowDuplicateRegistration}
+   *
+   * @return true if duplicate registration is allowed, false otherwise (default: false)
+   */
+  public boolean getAllowDuplicateRegistration() {
+    return allowDuplicateRegistration != null && allowDuplicateRegistration;
+  }
+
+  /**
+   * Note that this will remove entries from {@code properties}. This is because we want to know if
+   * there are unused properties remaining after all properties have been loaded.
+   */
+  static RegistryProperties load(Map<Object, Object> properties)
+      throws PrometheusPropertiesException {
+    Boolean allowDuplicateRegistration =
+        Util.loadBoolean(PREFIX + "." + ALLOW_DUPLICATE_REGISTRATION, properties);
+    return new RegistryProperties(allowDuplicateRegistration);
+  }
+
+  public static Builder builder() {
+    return new Builder();
+  }
+
+  public static class Builder {
+
+    @Nullable private Boolean allowDuplicateRegistration;
+
+    private Builder() {}
+
+    /** See {@link RegistryProperties#getAllowDuplicateRegistration()} */
+    public Builder allowDuplicateRegistration(boolean allowDuplicateRegistration) {
+      this.allowDuplicateRegistration = allowDuplicateRegistration;
+      return this;
+    }
+
+    public RegistryProperties build() {
+      return new RegistryProperties(allowDuplicateRegistration);
+    }
+  }
+}