feat: Add telemetry support. #463

ehsavoie · 2025-11-18T15:54:42Z

Adding support for OpenTelemetry

Fixes #388 🦕

gemini-code-assist · 2025-11-18T15:55:20Z

Summary of Changes

Hello @ehsavoie, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request integrates OpenTelemetry into the A2A Java SDK, providing robust distributed tracing capabilities. The changes enable automatic span creation for both client-initiated and server-processed A2A requests, offering deeper visibility into the flow of operations. This enhancement is crucial for monitoring, troubleshooting, and understanding the performance characteristics of applications built with the SDK.

Highlights

OpenTelemetry Module: Introduced a new Maven module, extras/opentelemetry, to encapsulate all OpenTelemetry integration logic for the A2A Java SDK.
Client-Side Tracing: Implemented dynamic wrapping of ClientTransport instances with OpenTelemetryClientTransport within the ClientBuilder. This allows for automatic tracing of client-side A2A interactions when an OpenTelemetry Tracer is provided in the ClientTransportConfig.
Server-Side Tracing Interceptors: Added a new @Trace annotation and SpanInterceptor mechanism to enable automatic distributed tracing for server-side request handler methods across gRPC, JSON-RPC, and REST protocols. Custom AttributeExtractor implementations are used to enrich spans with relevant request details.
Enhanced ClientTransportConfig: The ClientTransportConfig now includes a generic parameters map, facilitating the injection of arbitrary configuration, such as the OpenTelemetry Tracer instance, into transport implementations.
Example Application Updates: The helloworld example client and server applications have been updated to demonstrate the setup and usage of OpenTelemetry, including dependency additions and configuration for tracing.

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Code Review

This pull request adds support for OpenTelemetry, which is a great addition for observability. The implementation introduces a new opentelemetry extras module and integrates tracing on both the client and server sides. On the client side, it uses reflection for optional wrapping, and on the server side, it uses CDI interceptors with a new @Trace annotation. My review focuses on improving the robustness and maintainability of this new feature. I've found a few critical issues, such as a ClassCastException in an attribute extractor and silent exception swallowing that could make debugging difficult. I've also identified several opportunities for code cleanup, such as fixing typos, removing duplicated code, and improving the design of the CDI interceptor to better support dependency injection. Addressing these points will make the OpenTelemetry integration more solid and easier to maintain.

transport/rest/src/main/java/io/a2a/transport/rest/handler/RestAttributeExtractor.java

client/base/src/main/java/io/a2a/client/ClientBuilder.java

...as/opentelemetry/src/main/java/io/a2a/extras/opentelemetry/OpenTelemetryClientTransport.java

extras/opentelemetry/src/main/java/io/a2a/extras/opentelemetry/SpanInterceptor.java

...as/opentelemetry/src/main/java/io/a2a/extras/opentelemetry/OpenTelemetryClientTransport.java

extras/opentelemetry/src/main/java/io/a2a/extras/opentelemetry/SpanInterceptor.java

transport/grpc/src/main/java/io/a2a/transport/grpc/handler/GrpcHandler.java

transport/grpc/src/main/java/io/a2a/transport/grpc/handler/GrpctAttributeExtractor.java

brunobat

I think you need to decide if you are creating your own instrumentation annotations and API or if you just reuse the ones provided by OTel.

Also, the attribute names, should follow these semantic conventions, as much as possible: https://opentelemetry.io/docs/specs/semconv/gen-ai/gen-ai-agent-spans/

server-common/src/main/java/io/a2a/server/interceptors/Trace.java

server-common/src/main/java/io/a2a/server/interceptors/AttributeExtractor.java

server-common/src/main/java/io/a2a/server/interceptors/Kind.java

...as/opentelemetry/src/main/java/io/a2a/extras/opentelemetry/OpenTelemetryClientTransport.java

examples/helloworld/client/src/main/java/io/a2a/examples/helloworld/HelloWorldClient.java

kabir

A few things which may or may not be needed :-)

kabir · 2025-11-21T11:23:49Z

client/base/src/main/java/io/a2a/client/ClientBuilder.java

    private final List<BiConsumer<ClientEvent, AgentCard>> consumers = new ArrayList<>();
-    private @Nullable Consumer<Throwable> streamErrorHandler;
+    private @Nullable
+    Consumer<Throwable> streamErrorHandler;


This looks a bit strange :-)

The original looks better, but I think

@Nullable private Consumer<Throwable> streamErrorHandler;

would look better. But I see we have private @Nullable .... 'everywhere' :-)

kabir · 2025-11-21T11:33:09Z

extras/opentelemetry/src/main/java/io/a2a/extras/opentelemetry/SpanInterceptor.java

+                        .extractor();
+
+        String name = jakartaContext.getTarget().getClass().getName();
+        if (name != null && name.endsWith("_Subclass")) {


name cannot be null

kabir · 2025-11-21T11:37:08Z

server-common/src/main/java/io/a2a/server/requesthandlers/RequestHandlerAttributeExtractor.java

+                    return Map.of("request", parameters[0].toString(), "extensions", context.getActivatedExtensions().stream().collect(Collectors.joining(",")), "a2a.method", (String) context.getState().get("method"));
+                }
+                default -> {
+                    return Collections.emptyMap();


Maybe we could log a warning here. Or if the intent is that all DefaultRequestHandler methods are handled, we could throw an error?

kabir · 2025-11-21T11:37:36Z

transport/grpc/src/main/java/io/a2a/transport/grpc/handler/GrpcAttributeExtractor.java

+                    return Map.of("request", parameters[0].toString(), "extensions", GrpcContextKeys.EXTENSIONS_HEADER_KEY.get(), "a2a.method", GrpcContextKeys.GRPC_METHOD_NAME_KEY.get(currentContext));
+                }
+                default -> {
+                    return Collections.emptyMap();


log warn/throw error as above

kabir · 2025-11-21T11:38:07Z

transport/jsonrpc/src/main/java/io/a2a/transport/jsonrpc/handler/JsonRPCAttributeExtractor.java

+                    return Map.of("body", parameters[0].toString(), "extensions", context.getActivatedExtensions().stream().collect(Collectors.joining(",")), "a2a.method", (String) context.getState().get(METHOD_NAME_KEY));
+                }
+                default -> {
+                    return Collections.emptyMap();


kabir · 2025-11-21T11:38:29Z

transport/rest/src/main/java/io/a2a/transport/rest/handler/RestAttributeExtractor.java

+                    return Map.of("contextId", (String) parameters[0], "status", (String) parameters[1], "extensions", context.getActivatedExtensions().stream().collect(Collectors.joining(",")), "a2a.method", (String) context.getState().get(METHOD_NAME_KEY));
+                }
+                default -> {
+                    return Collections.emptyMap();


kabir

Actually, @ehsavoie it looks like you are adding Otel tracing to the example. But I don't know how to enable this etc.
Can you update the README with instructions?

Maybe we could also make this example testable in the CI, like we do for the cloud-deployment one?

Also, it would be good to have some tests in the extras module

* Adding an annotation that can be used by CDI interceptor to create spans on current exchanges. * Adding support for client wrappers to be able to add client side spans. * Updating the helloworld example to use opentelemetry. Fixing issue a2aproject#388 Signed-off-by: Emmanuel Hugonnet <[email protected]>

ehsavoie requested review from fjuma and kabir November 18, 2025 15:54

gemini-code-assist bot reviewed Nov 18, 2025

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brunobat reviewed Nov 18, 2025

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ehsavoie force-pushed the issue_388 branch 4 times, most recently from 7661dd6 to 893ce8b Compare November 20, 2025 13:57

ehsavoie changed the title ~~Issue 388~~ feat: Add telemetry support. Nov 20, 2025

ehsavoie force-pushed the issue_388 branch 2 times, most recently from 22a2af4 to d35543a Compare November 20, 2025 14:46

ehsavoie requested a review from brunobat November 20, 2025 20:41

kabir reviewed Nov 21, 2025

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kabir requested changes Nov 21, 2025

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ehsavoie force-pushed the issue_388 branch from d35543a to d5cfb1d Compare November 26, 2025 13:29

feat: Add telemetry support. #463

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feat: Add telemetry support. #463

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ehsavoie commented Nov 18, 2025

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