feat(opentelemetry): record A2A operation duration metrics

Signed-off-by: Emmanuel Hugonnet <ehugonne@redhat.com>

Author: ehsavoie

docs/content/dev/extra/opentelemetry.md

@@ -14,6 +14,7 @@ Adds distributed tracing and context propagation to A2A servers and clients usin
 - **Context Propagation**: OpenTelemetry trace context propagation across async operations
 - **Request/Response Logging**: Optional extraction of request and response data into spans
 - **Error Tracking**: Automatic error status and error type attributes on failures
+- **Metrics**: `gen_ai.client.operation.duration` histogram on the client side; `gen_ai.agent.a2a.streaming.duration` histogram for full streaming lifecycle on the server side
 
 ## Modules
 
@@ -115,6 +116,24 @@ Each span event on Span₂ carries:
 | `gen_ai.agent.a2a.streaming-event` | `toString()` of the published `StreamingEventKind` |
 | `gen_ai.agent.a2a.status.code` | `OK` |
 
+### Metrics
+
+The server decorator records the following histogram instruments:
+
+| Instrument | Type | Unit | Description |
+|------------|------|------|-------------|
+| `gen_ai.agent.a2a.streaming.duration` | Histogram | `s` | Duration from stream initiation to last event, for `message/stream` and `tasks/resubscribe` |
+
+Attributes on `gen_ai.agent.a2a.streaming.duration`:
+
+| Attribute | Value |
+|-----------|-------|
+| `gen_ai.agent.a2a.operation.name` | A2A method name (`message/stream` or `tasks/resubscribe`) |
+| `gen_ai.system` | `a2a` |
+| `error.type` | `error` (only on stream failure) |
+
+Meter injection uses CDI `Instance<Meter>`, so the histogram is silently skipped if no `Meter` bean is available in the container.
+
 ### Context-Aware Async Executor
 
 > **Note:** The `AsyncManagedExecutorProducer` is provided by the **Quarkus reference server** ([`reference/common`](https://github.com/a2aproject/a2a-java/blob/main/reference/common/src/main/java/org/a2aproject/sdk/server/common/quarkus/AsyncManagedExecutorProducer.java)), not the OpenTelemetry module. It is documented here because it enables context propagation (including trace context) across async boundaries.
@@ -174,7 +193,7 @@ Enable request and response data extraction in spans using JVM system properties
 
 ### Instrumentation
 
-Adds OpenTelemetry spans to A2A client operations:
+Adds OpenTelemetry spans and metrics to A2A client operations:
 
 ```xml
 <dependency>
@@ -183,6 +202,27 @@ Adds OpenTelemetry spans to A2A client operations:
 </dependency>
 ```
 
+To also enable `gen_ai.client.operation.duration` metrics, pass a `Meter` via the transport config:
+
+```java
+config.setParameters(Map.of(
+    OpenTelemetryClientTransportWrapper.OTEL_TRACER_KEY, openTelemetry.getTracer("my-service"),
+    OpenTelemetryClientTransportWrapper.OTEL_METER_KEY,  openTelemetry.getMeter("my-service")
+));
+```
+
+| Instrument | Type | Unit | Description |
+|------------|------|------|-------------|
+| `gen_ai.client.operation.duration` | Histogram | `s` | Duration of each A2A client operation call |
+
+Attributes on `gen_ai.client.operation.duration`:
+
+| Attribute | Value |
+|-----------|-------|
+| `gen_ai.agent.a2a.operation.name` | A2A method name (e.g. `message/send`) |
+| `gen_ai.system` | `a2a` |
+| `error.type` | `error` (only on failure) |
+
 ### Context Propagation
 
 For trace context propagation across async client boundaries:

examples/helloworld/client/README.md

@@ -161,11 +161,11 @@ The Java client (`HelloWorldClient.java`) performs the following actions:
 
 ## Enable OpenTelemetry (Optional)
 
-The client includes support for distributed tracing with OpenTelemetry. To enable it:
+The client includes support for distributed tracing and metrics with OpenTelemetry. To enable it:
 
 ### Prerequisites
 
-**IMPORTANT**: The client expects an OpenTelemetry collector to be ready and accepting traces. You have two options:
+**IMPORTANT**: The client expects an OpenTelemetry collector to be ready and accepting traces and metrics. You have two options:
 
 #### Option 1: Use the Java Server Example (Recommended)
 

examples/helloworld/client/src/main/java/org/a2aproject/sdk/examples/helloworld/client/HelloWorldClient.java

@@ -1,5 +1,6 @@
 package org.a2aproject.sdk.examples.helloworld.client;
 
+import static org.a2aproject.sdk.extras.opentelemetry.client.OpenTelemetryClientTransportWrapper.OTEL_METER_KEY;
 import static org.a2aproject.sdk.extras.opentelemetry.client.OpenTelemetryClientTransportWrapper.OTEL_TRACER_KEY;
 import static org.a2aproject.sdk.extras.opentelemetry.client.propagation.OpenTelemetryClientPropagatorTransportWrapper.OTEL_OPEN_TELEMETRY_KEY;
 
@@ -34,8 +35,11 @@
 import io.grpc.ManagedChannelBuilder;
 import io.opentelemetry.api.trace.propagation.W3CTraceContextPropagator;
 import io.opentelemetry.context.propagation.ContextPropagators;
+import io.opentelemetry.exporter.otlp.metrics.OtlpGrpcMetricExporter;
 import io.opentelemetry.exporter.otlp.trace.OtlpGrpcSpanExporter;
 import io.opentelemetry.sdk.OpenTelemetrySdk;
+import io.opentelemetry.sdk.metrics.SdkMeterProvider;
+import io.opentelemetry.sdk.metrics.export.PeriodicMetricReader;
 import io.opentelemetry.sdk.resources.Resource;
 import io.opentelemetry.sdk.trace.SdkTracerProvider;
 import io.opentelemetry.sdk.trace.export.BatchSpanProcessor;
@@ -136,20 +140,32 @@ public static void main(String[] args) {
     }
 
     static OpenTelemetrySdk initOpenTelemetry() {
+        Resource resource = Resource.getDefault().toBuilder()
+                .put("service.version", "1.0")
+                .put("service.name", "helloworld-client")
+                .build();
+
         SdkTracerProvider sdkTracerProvider = SdkTracerProvider.builder()
                 .addSpanProcessor(BatchSpanProcessor.builder(
                         OtlpGrpcSpanExporter.builder()
                                 .setEndpoint("http://localhost:5317")
                                 .build()
                 ).build())
-                .setResource(Resource.getDefault().toBuilder()
-                        .put("service.version", "1.0")
-                        .put("service.name", "helloworld-client")
-                        .build())
+                .setResource(resource)
+                .build();
+
+        SdkMeterProvider sdkMeterProvider = SdkMeterProvider.builder()
+                .registerMetricReader(PeriodicMetricReader.builder(
+                        OtlpGrpcMetricExporter.builder()
+                                .setEndpoint("http://localhost:5317")
+                                .build()
+                ).build())
+                .setResource(resource)
                 .build();
 
         return OpenTelemetrySdk.builder()
                 .setTracerProvider(sdkTracerProvider)
+                .setMeterProvider(sdkMeterProvider)
                 .setPropagators(ContextPropagators.create(W3CTraceContextPropagator.getInstance()))
                 .build();
     }
@@ -186,6 +202,7 @@ private static void updateTransportConfig(ClientTransportConfig transportConfig,
         if (openTelemetrySdk != null) {
             Map<String, Object> parameters = new HashMap<>(transportConfig.getParameters());
             parameters.put(OTEL_TRACER_KEY, openTelemetrySdk.getTracer("helloworld-client"));
+            parameters.put(OTEL_METER_KEY, openTelemetrySdk.getMeter("helloworld-client"));
             parameters.put(OTEL_OPEN_TELEMETRY_KEY, openTelemetrySdk);
             transportConfig.setParameters(parameters);
         }

examples/helloworld/server/src/main/resources/application.properties

@@ -5,6 +5,7 @@ quarkus.agentcard.protocol=JSONRPC
 
 # OpenTelemetry configuration
 quarkus.otel.sdk.disabled=false
+quarkus.otel.metrics.enabled=true
 quarkus.observability.lgtm.grafana-port=3001
 quarkus.observability.lgtm.otel-grpc-port=5317
 quarkus.observability.lgtm.otel-http-port=5318