Add A2A (Agent-to-Agent) protocol support by minorun365 · Pull Request #217 · aws/bedrock-agentcore-sdk-python

minorun365 · 2026-01-18T10:28:50Z

Summary

This PR adds support for the A2A (Agent-to-Agent) protocol, enabling agents to communicate with each other using the JSON-RPC 2.0 protocol.

New Features

BedrockAgentCoreA2AApp: A Starlette-based application class for hosting A2A agents
AgentCard & AgentSkill: Models for describing agent capabilities
@entrypoint decorator: For defining message handlers
JSON-RPC 2.0 support: Standard A2A protocol implementation on port 9000

New Files

src/bedrock_agentcore/runtime/a2a_app.py - Main A2A application class
src/bedrock_agentcore/runtime/a2a_models.py - A2A data models
tests/bedrock_agentcore/runtime/test_a2a_app.py - Unit tests for A2A app
tests/bedrock_agentcore/runtime/test_a2a_models.py - Unit tests for A2A models

Usage Example

from bedrock_agentcore.runtime import AgentCard, AgentSkill, BedrockAgentCoreA2AApp

agent_card = AgentCard(
    name="My Agent",
    description="A helpful assistant",
    version="1.0.0",
    skills=[AgentSkill(id="qa", name="Q&A", description="Answer questions")],
)

app = BedrockAgentCoreA2AApp(agent_card=agent_card)

@app.entrypoint
async def handle_message(request, context):
    user_text = request.params.get("message", {}).get("parts", [{}])[0].get("text", "")
    return {"artifacts": [{"parts": [{"kind": "text", "text": f"Response to: {user_text}"}]}]}

if __name__ == "__main__":
    app.run()

Test Plan

All 54 unit tests pass
Linter checks pass
Tested locally with curl commands
Deployed to AgentCore Runtime and verified working

@entrypoint

- Add BedrockAgentCoreA2AApp class for hosting A2A agents - Add A2A models (AgentCard, AgentSkill, JsonRpcRequest/Response, etc.) - Add @entrypoint decorator for message handling - Support JSON-RPC 2.0 protocol on port 9000 - Export A2A classes from runtime module - Add comprehensive unit tests (54 tests)

Moophic · 2026-03-02T20:25:18Z

@sundargthb,
Can we get this beautiful PR reviewed and merged please?

sundargthb · 2026-03-11T22:09:39Z

src/bedrock_agentcore/runtime/a2a_models.py

+from urllib.parse import quote
+
+
+class JsonRpcErrorCode(int, Enum):


the codes here match this page but contradicts with the A2A Protocol contract page.. need to check the valid range

sundargthb · 2026-03-11T22:13:47Z

src/bedrock_agentcore/runtime/a2a_app.py

+            return JSONResponse(card_dict)
+        except Exception as e:
+            self.logger.exception("Failed to serve Agent Card")
+            return JSONResponse({"error": str(e)}, status_code=500)


str(e) is passed directly into the JSON-RPC error response. ... internal exception details (paths, library errors, connection strings) can reach external agents ? the HTTP app.py has the same str(e) pattern — so this isn't new to the PR, it's consistent with existing code. But A2A is explicitly cross-organizational (A2A Enterprise Features)

sundargthb · 2026-03-11T22:15:19Z

src/bedrock_agentcore/runtime/a2a_app.py

+            self.logger.exception("Request failed (%.3fs)", duration)
+            return self._jsonrpc_error_response(
+                body.get("id") if "body" in dir() else None,
+                JsonRpcErrorCode.INTERNAL_ERROR,


same comment as _handle_agent_card..

sundargthb · 2026-03-11T22:20:08Z

src/bedrock_agentcore/runtime/a2a_app.py

+)
+
+
+class A2ARequestContextFormatter(logging.Formatter):


The HTTP app has @async_task, add_async_task()/complete_async_task(), and force_ping_status()/clear_forced_ping_status(). Without these, developers can't signal HealthyBusy during long-running agent workflows, which means the runtime may incorrectly scale down or over-route. Can either finish the port from app.py or remove the unused attributes/logic

Add missing A2A protocol standard error codes (-32001 to -32007) alongside existing AgentCore Runtime error codes (-32501 to -32505). The two sets serve different layers: protocol-level (task management) vs infrastructure-level (throttling, resource management). Added corresponding tests. Addresses review feedback on PR aws#217 regarding error code alignment between A2A protocol spec and AWS AgentCore documentation. https://claude.ai/code/session_01Fnc4LHzBPBej7FK7ooT2La

- Remove unused imports (JsonRpcRequest, pytest) in tests - Initialize body=None before try block; replace `"body" in dir()` with `body is not None` - Add `isinstance(body, dict)` guard so non-object JSON payloads return INVALID_REQUEST (-32600) instead of INTERNAL_ERROR (-32603) - Use `_convert_to_serializable()` / `_safe_serialize_to_json_string()` for both streaming and non-streaming paths so dataclass helpers (A2AArtifact, etc.) serialize correctly - Fall back to `request.base_url` when AGENTCORE_RUNTIME_URL is unset so the agent card always contains a reachable URL - Add tests for dataclass serialization (sync + streaming) and non-object payload rejection

minorun365 · 2026-03-12T07:39:01Z

@sundargthb Thanks for your review! Fixed it.

codecov-commenter · 2026-03-12T12:22:46Z

Codecov Report

❌ Patch coverage is 85.48813% with 55 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@52bc194). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/bedrock_agentcore/runtime/a2a_app.py	81.22%	34 Missing and 12 partials ⚠️
src/bedrock_agentcore/runtime/a2a_models.py	93.18%	3 Missing and 6 partials ⚠️

Additional details and impacted files

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  Branches        ?      664           
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  Misses          ?      240           
  Partials        ?      185

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padmak30 · 2026-03-11T20:33:24Z

src/bedrock_agentcore/runtime/a2a_models.py

+    VALIDATION_ERROR = -32502
+    THROTTLING = -32503
+    RESOURCE_CONFLICT = -32504
+    RUNTIME_CLIENT_ERROR = -32505


Invalid error codes https://docs.aws.amazon.com/bedrock-agentcore/latest/devguide/runtime-a2a-protocol-contract.html#error-handling

padmak30 · 2026-03-11T20:42:57Z

src/bedrock_agentcore/runtime/a2a_models.py

+    """
+    # URL encode the ARN (safe='' means encode all special characters)
+    escaped_arn = quote(agent_arn, safe="")
+    return f"https://bedrock-agentcore.{region}.amazonaws.com/runtimes/{escaped_arn}/invocations/"


Region can be parsed from the ARN

padmak30 · 2026-03-11T21:40:31Z

src/bedrock_agentcore/runtime/a2a_app.py

+            if asyncio.iscoroutinefunction(handler):
+                return await handler(*args)
+            else:
+                loop = asyncio.get_event_loop()


get_event_loop is deprecated for Python 3.10+
Use run_in_threadpool similar to app.py

padmak30 · 2026-03-12T21:32:58Z

src/bedrock_agentcore/runtime/a2a_app.py

+        return json.dumps(log_entry, ensure_ascii=False)
+
+
+class BedrockAgentCoreA2AApp(Starlette):


There should be a common app instead of one per protocol. We could have the App take in a protocol parameter to instantiate the right protocol and default to http.
Also we should use the A2A SDK, a lot of stuff around agent-card, json rpc comes built-in.

- Fix A2A error codes to match the A2A protocol specification (-32001 to -32006) - Parse region from ARN in build_runtime_url instead of requiring a separate parameter - Replace deprecated asyncio.get_event_loop() with starlette's run_in_threadpool - Sanitize error messages in JSON-RPC responses to avoid leaking internal details https://claude.ai/code/session_012D4PLASRQsAhZadWYqaPim

… async task lifecycle - Sanitize str(e) in _handle_agent_card to avoid leaking internal details (comment aws#3) - Port async task lifecycle methods from app.py: async_task decorator, add_async_task, complete_async_task, force_ping_status, clear_forced_ping_status, get_async_task_info (comment aws#2) - These methods enable developers to signal HealthyBusy status during long-running A2A workflows, preventing incorrect scaling decisions https://claude.ai/code/session_012D4PLASRQsAhZadWYqaPim

minorun365 · 2026-03-13T14:53:06Z

@padmak30
Thank you for your review. Fixed it!
As for using A2A SDK, I think we should try it in another PR because it will be a large PR.

tejaskash · 2026-03-13T21:32:02Z

@minorun365 Thanks for putting this together — A2A support is an important addition and we appreciate the effort here, especially revising this PR multiple times.

After reviewing this against the A2A spec and looking at how other frameworks (ADK, Strands, CrewAI, LangGraph, Pydantic AI) approach A2A, we had an internal discussion and decided to go in a different direction for developer experience. The core issue is that the A2A protocol's task lifecycle and streaming model don't map cleanly to the @app.entrypoint decorator pattern and the industry has largely converged on the official a2a-sdk rather than custom implementations.

We're working on a new proposal that leans on the official a2a-sdk as a dependency and focuses our code on the AgentCore-specific value-add (runtime headers, health checks, deployment defaults). We'll be sending out a PR for this by the end of the month . This is a short snippet of what we're thinking of developing.

from bedrock_agentcore.runtime.a2a import serve_a2a

# Google ADK
from google.adk.a2a.executor import A2aAgentExecutor
serve_a2a(agent_card=card, executor=A2aAgentExecutor(runner=runner))

# Strands
from strands.multiagent.a2a.executor import StrandsA2AExecutor
serve_a2a(agent_card=card, executor=StrandsA2AExecutor(agent))

Closing this one out, but thank you again for your contribution to A2A support, and we welcome future . I will make sure to tag you on the new PR to get your input.

minorun365 temporarily deployed to manual-approval January 18, 2026 10:29 — with GitHub Actions Inactive

sundargthb reviewed Mar 11, 2026

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minorun365 requested a review from a team March 12, 2026 06:48

minorun365 requested a deployment to manual-approval March 12, 2026 06:48 — with GitHub Actions Waiting

minorun365 force-pushed the feature/a2a-protocol-support branch from 0a85319 to ee117a9 Compare March 12, 2026 07:30

minorun365 requested a deployment to manual-approval March 12, 2026 07:30 — with GitHub Actions Waiting

minorun365 requested a deployment to manual-approval March 12, 2026 18:14 — with GitHub Actions Waiting

Improve test coverage from 85% to 99%

8c9cd91

minorun365 force-pushed the feature/a2a-protocol-support branch from 679bab9 to 8c9cd91 Compare March 12, 2026 18:15

minorun365 requested a deployment to manual-approval March 12, 2026 18:15 — with GitHub Actions Waiting

padmak30 reviewed Mar 12, 2026

View reviewed changes

claude and others added 3 commits March 13, 2026 02:23

レビュー指摘対応: エラーコード修正、contextvars復元、テスト追加

d5414fa

minorun365 requested a deployment to manual-approval March 13, 2026 04:04 — with GitHub Actions Waiting

共通ベースクラス _BaseAgentCoreApp を抽出してHTTPとA2Aの重複コードを削減

ef1e784

minorun365 requested a deployment to manual-approval March 13, 2026 04:14 — with GitHub Actions Waiting

A2A E2E統合テストを追加

aec598d

minorun365 requested a deployment to manual-approval March 13, 2026 04:20 — with GitHub Actions Waiting

tejaskash closed this Mar 13, 2026

		from urllib.parse import quote


		class JsonRpcErrorCode(int, Enum):

		return json.dumps(log_entry, ensure_ascii=False)


		class BedrockAgentCoreA2AApp(Starlette):

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minorun365 commented Jan 18, 2026

Summary

New Features

New Files

Usage Example

Test Plan

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minorun365 commented Mar 12, 2026

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minorun365 commented Mar 13, 2026

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Moophic commented Mar 2, 2026 •

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