Event Bus

The event bus is an infrastructure service that provides the ability to reliably pass events between different servers.

There are many different implementations with greater or lesser reliability and performance. Many organizations establish a standard choice of their event bus service.

Egeria uses Apache Kafka as its default event bus implementation. However, to allow other event bus implementations to be plugged into the OMAG servers, all calls to the event bus are issued through an event bus connector.

Details of the event bus connector is added to a server’s configuration document using the Event Bus Config. The event bus config establishes a set of defaults for the event bus. These defaults are then used whenever Egeria components that use the event bus are configured.

Figure 1 shows the event bus in action.

Figure 1

Figure 1: The event bus in use by OMAG servers and other technologies

It is hosting a number of topics. Each topic manages the event exchange for a particular collection of events. For example, the OMRS Cohort Topic manages repository services events.

The components using the event bus have a specialized connector that supports event exchange for a specific collection of event. Since it is necessary to be able to swap the event bus implementation, These connectors embed a generic topic connector for the type of event bus in use. This is illustrated in Figure 2.

Figure 2

Figure 2: Nested topic connectors

The configuration for these nested connectors is illustrated in Figure 3.

Figure 3

Figure 3: Embedded event bus configuration

  1. The connector for the event bus topic is identified and configured using the Event Bus Config.

  2. This configuration is encoded in a Connection object for the generic event bus topic connector.

  3. When the consuming component is configured, a Connection object for its specialized topic connector is created, with the generic event bus topic connector embedded inside.

  4. When the Connector Broker is called upon to create the specialized topic connector at server start up, it navigates the hierarchy of Connection objects, creating the nested hierarchy of connectors as specified.

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