goplt/docs/content/adr/0023-event-bus-implementation.md

ADR-0023: Event Bus Implementation

Status

Accepted

Context

The platform needs an event bus for:

• Module-to-module communication
• Decoupled event publishing
• Event sourcing (optional, future)
• Integration with external systems

Options considered:

1. In-process channel-based bus - Simple, for development/testing
2. Kafka - Production-grade, scalable
3. RabbitMQ - Alternative message broker
4. Redis pub/sub - Simple but less reliable

Decision

Support dual implementation with in-process primary, Kafka for production:

1. In-process bus (default):

   • Channel-based implementation
   • Used for development, testing, small deployments
   • Simple, no external dependencies

2. Kafka bus (production):

   • Full Kafka integration via segmentio/kafka-go
   • Producer/consumer groups
   • Configurable via environment (switch implementation)

Rationale:

• In-process bus is simple for development
• Kafka provides production-grade reliability and scalability
• Interface abstraction allows swapping
• Modules don't need to know which implementation
• Can start simple and scale up

Consequences

Positive

• Simple for development (no Kafka needed)
• Scalable for production (Kafka)
• Flexible (can choose implementation)
• Modules are decoupled from implementation

Negative

• Two implementations to maintain
• Need to ensure interface covers both use cases
• Kafka adds infrastructure complexity

Implementation Notes

• Create pkg/eventbus/eventbus.go interface
• Implement internal/infra/bus/inprocess_bus.go (channel-based)
• Implement internal/infra/bus/kafka_bus.go (Kafka)
• Select implementation via config
• Support both sync and async event publishing
• Handle errors gracefully (retry, dead letter queue)