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Subscriptions

Chronicle supports subscriptions between event stores, allowing events to flow between them in a controlled, persistent, and observable way. This is particularly useful in distributed systems where different services own separate event stores but need to react to each other’s events.

Core Concepts

Section titled “Core Concepts”

Subscriptions in Chronicle are built around the outbox/inbox pattern and two complementary subscription modes:

  • Outbox — an event store publishes events to a well-known sequence so other stores can subscribe
  • Inbox — an event store maintains one inbox sequence per source it subscribes to, receiving forwarded events automatically
  • Implicit Subscriptions — automatic routing based on [EventStore] attributes on event types
  • Explicit Subscriptions — manual subscription setup using the Subscribe() API

Chronicle manages the subscription lifecycle on the Kernel side. Subscriptions survive client disconnections and are automatically re-established when the Kernel starts.

Choosing Between Implicit and Explicit Subscriptions

Section titled “Choosing Between Implicit and Explicit Subscriptions”

Implicit subscriptions are best when event types are published in a NuGet package. The source service annotates events with [EventStore("service-name")], and consuming services simply reference the package and observe the events—Chronicle handles routing automatically.

Explicit subscriptions give you fine-grained control. Use them when you need to filter specific event types, when events are not in a shared package, or when subscription configuration must be dynamic.

Topics

Section titled “Topics”