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Event Hub — Cross-Service Event Delivery and Routing

Overview​

Event Hub is the event-driven communication layer of the Keymate platform. It accepts events from upstream services through a single gRPC endpoint, reliably persists them using a relational database-backed Transactional Outbox pattern, and forwards them to event bus topics via scheduler-based mechanisms. This architecture eliminates the direct event bus dependency from source services and prevents message loss.

Event Hub supports multiple event categories — it routes each to its own dedicated event bus topic and serializes them in Protobuf format through Schema Registry. Teams can add new event types by registering additional channels and use cases.

When to Read This Section​

  • You want to send events from a service to Event Hub
  • You want to understand the outbox-based event delivery mechanism
  • You want to learn about the event bus topic structure and consumer contracts
  • You want to configure and monitor Event Hub in a production environment

Who Should Start Here​

  • Developer — Developers integrating with the Event Hub gRPC API or building event bus consumers
  • Architect — Architects evaluating event-driven architecture decisions and cross-service communication patterns
  • Operator — Operations engineers deploying Event Hub, configuring schedulers, and monitoring the outbox table

Key Topics​

Overview

What Event Hub is, why it exists, and how the Transactional Outbox pattern works.

Delivery & Subscription Model

Event bus topic structure, scheduler-based fan-out mechanism, and Protobuf serialization model.

Outbox Replay & DLQ

Event lifecycle in the outbox table, retry strategy, and failed event management.

Consumer Contracts

Event schemas, compatibility rules, and Protobuf contract surface for event bus consumers.

Representative Journeys​

  1. Overview — Understand Event Hub's role and architecture
  2. Delivery & Subscription Model — Learn topic structure and delivery semantics
  3. Outbox Replay & DLQ — Understand reliability and error management
  4. Consumer Contracts — Review consumer-side expectations and schema contracts