feat: Replicated Queue Manager based on Mp Reactive Messaging with Kafka #309

kabir · 2025-09-29T16:44:30Z

It is implemented in such a way that the replication mechanism can be swapped with something else

gemini-code-assist · 2025-09-29T16:45:01Z

Summary of Changes

Hello @kabir, 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 delivers a crucial feature for distributed A2A deployments: a replicated queue manager. It enables events generated within one A2A instance to be propagated to others via a message broker, ensuring consistency across the system. The architecture is designed for extensibility, allowing for various replication strategies, with an initial focus on MicroProfile Reactive Messaging and Kafka. This enhancement significantly improves the scalability and resilience of A2A applications.

Highlights

New Replicated Queue Manager: Introduces a new ReplicatedQueueManager that wraps the existing InMemoryQueueManager to enable event replication across multiple A2A instances.
Pluggable Replication Strategy: The design includes a ReplicationStrategy interface, allowing different replication mechanisms to be easily swapped. An initial implementation using MicroProfile Reactive Messaging with Kafka is provided.
Event Serialization: Events are serialized using Jackson with polymorphic type information, ensuring proper type preservation during replication and deserialization.
Core Event Queue Enhancements: The core EventQueue and QueueManager interfaces have been updated to support EventEnqueueHook and EventQueueFactory for more flexible queue creation and event interception.
Comprehensive Testing: Includes new unit tests for the core replication logic and serialization, as well as integration tests to verify end-to-end Kafka replication within a Quarkus environment.

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gemini-code-assist

Code Review

This pull request introduces a new replicated queue manager, which is a significant and well-implemented feature. The architecture is extensible, allowing for different replication strategies. The initial implementation uses MicroProfile Reactive Messaging with Kafka, and it's accompanied by a good set of unit and integration tests.

My review focuses on improving code quality by addressing some minor issues like unused imports, inconsistent naming, and replacing System.out.println with proper logging. I also found some potentially dead code and a test case that could be improved. The use of ThreadLocal is a bit of a code smell, but it seems to be a contained workaround.

Overall, this is a great contribution.

...ed/core/src/main/java/io/a2a/extras/queuemanager/replicated/core/ReplicatedQueueManager.java

.../io/a2a/extras/queuemanager/replicated/mp_reactive/ReactiveMessagingReplicationStrategy.java

server-common/src/main/java/io/a2a/server/events/EventQueue.java

extras/README.md

...eplicated/core/src/main/java/io/a2a/extras/queuemanager/replicated/core/ReplicatedEvent.java

...ed/core/src/main/java/io/a2a/extras/queuemanager/replicated/core/ReplicatedQueueManager.java

...ed/core/src/test/java/io/a2a/extras/queuemanager/replicated/core/EventSerializationTest.java

...ore/src/test/java/io/a2a/extras/queuemanager/replicated/core/ReplicatedQueueManagerTest.java

...c/test/java/io/a2a/extras/queuemanager/replicated/tests/KafkaReplicationIntegrationTest.java

kabir · 2025-09-29T18:05:47Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces a significant new feature: a replicated queue manager using MicroProfile Reactive Messaging and Kafka. The overall architecture is well-designed, with a clear separation of concerns between the core replication logic and the specific messaging implementation. The use of a decorator pattern for ReplicatedQueueManager and the introduction of EventEnqueueHook and EventQueueFactory make the system extensible and robust.

The code is well-structured, and the inclusion of comprehensive unit and integration tests is commendable. I've identified a few areas for improvement, primarily concerning reliability in message handling and some minor maintainability issues. My main concern is about exception handling in the Kafka consumer, which could lead to message loss. Please see the detailed comments for specific suggestions.

.../io/a2a/extras/queuemanager/replicated/mp_reactive/ReactiveMessagingReplicationStrategy.java

extras/README.md

extras/queue-manager-replicated/README.md

...ed/core/src/main/java/io/a2a/extras/queuemanager/replicated/core/ReplicatedQueueManager.java

.../tests/src/test/java/io/a2a/extras/queuemanager/replicated/tests/TestKafkaEventConsumer.java

kabir · 2025-09-29T18:27:26Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces a robust and well-designed replicated queue manager using Kafka and MicroProfile Reactive Messaging. The architecture is clean, leveraging delegation, hooks, and factories to create an extensible system. The separation into core, implementation, and test modules is excellent, and the integration tests are comprehensive, covering both producing to and consuming from Kafka.

The refactoring of EventQueue and InMemoryQueueManager to support this extensibility is also well done.

I have a few minor suggestions to improve code quality and robustness, mainly concerning dependency management and error handling.

.../io/a2a/extras/queuemanager/replicated/mp_reactive/ReactiveMessagingReplicationStrategy.java

...ed/core/src/main/java/io/a2a/extras/queuemanager/replicated/core/ReplicatedQueueManager.java

extras/queue-manager-replicated/replication-mp-reactive/pom.xml

.../io/a2a/extras/queuemanager/replicated/mp_reactive/ReactiveMessagingReplicationStrategy.java

It is implemented in such a way that the replication mechanism can be swapped with something else

...ed/core/src/main/java/io/a2a/extras/queuemanager/replicated/core/ReplicatedQueueManager.java

…fka (a2aproject#309) It is implemented in such a way that the replication mechanism can be swapped with something else

gemini-code-assist bot reviewed Sep 29, 2025

View reviewed changes

kabir added 8 commits September 30, 2025 14:49

feat: Replicated Queue Manager based on Mp Reactive Messaging with Kafka

39e1949

It is implemented in such a way that the replication mechanism can be swapped with something else

Rename things and remove printlns

862813f

USe taskId when creating queue

b43b870

Fix test

2567b4e

Remove unused map

64a23f7

Clean up exception handling

95ff641

More review fixes

51c1f22

More review changes

26aad52

kabir force-pushed the replicated-eventqueues branch from 1187480 to 26aad52 Compare September 30, 2025 13:49

fjuma reviewed Sep 30, 2025

View reviewed changes

...ed/core/src/main/java/io/a2a/extras/queuemanager/replicated/core/ReplicatedQueueManager.java Show resolved Hide resolved

fjuma approved these changes Sep 30, 2025

View reviewed changes

Clean up beans.xml to get rid of warnings

576dd5f

kabir force-pushed the replicated-eventqueues branch from 38a3d32 to 576dd5f Compare October 1, 2025 09:40

kabir merged commit 1828b4d into a2aproject:main Oct 1, 2025
4 checks passed

kabir added a commit to kabir/a2a-java that referenced this pull request Dec 23, 2025

feat: Replicated Queue Manager based on Mp Reactive Messaging with Ka…

66d9b61

…fka (a2aproject#309) It is implemented in such a way that the replication mechanism can be swapped with something else

feat: Replicated Queue Manager based on Mp Reactive Messaging with Kafka #309

feat: Replicated Queue Manager based on Mp Reactive Messaging with Kafka #309

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kabir commented Sep 29, 2025

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gemini-code-assist bot commented Sep 29, 2025

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kabir commented Sep 29, 2025

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kabir commented Sep 29, 2025

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