An event bus is the core routing component in EventBridge. It receives events from sources, evaluates them against your event rules, and delivers matching events to specified targets. EventBridge provides two types of event buses: a default event bus for Alibaba Cloud service events, and custom event buses for your applications and existing message data.
How event routing works
Events flow through an event bus in three stages:
An event source publishes an event to an event bus. Alibaba Cloud services publish to the default event bus. Your applications and existing message data publish to a custom event bus.
EventBridge evaluates the event against rules. Each rule defined on the bus checks whether the event matches its filter pattern.
EventBridge delivers matching events to targets. For each rule that matches, EventBridge sends the event to the targets specified in that rule.
For example, you can create a rule on the default event bus that matches instance state changes in Elastic Compute Service (ECS). When an ECS instance enters the Running state, EventBridge delivers the event to a specified target, such as a Function Compute function or a message queue.
Event bus types
EventBridge provides two types of event buses. Each type accepts events from specific sources.
| Type | Description | Event sources | Managed by |
|---|---|---|---|
| Default event bus | A built-in event bus preconfigured in your account. Cannot be modified. | Alibaba Cloud services only | EventBridge |
| Custom event bus | An event bus that you create and manage. | Custom applications and existing message data only | You |
Default event bus
The default event bus receives events from Alibaba Cloud services. It is preconfigured in your account and cannot be modified.
Alibaba Cloud service events can be published only to the default event bus. Use the default event bus to monitor and respond to changes across your Alibaba Cloud resources. For example:
Trigger a Function Compute function when a cloud resource changes state.
Send a notification when a specific API operation occurs.
Start a workflow when an Alibaba Cloud service emits an alert event.
Custom event bus
A custom event bus receives events from your applications or existing message data. You create and manage custom event buses.
Events from custom applications or existing message data can be published only to a custom event bus. Use a custom event bus to route events from your own services or integrate existing message workflows into an event-driven architecture. For example:
Process order events from a microservice.
Route user activity events to a data analytics pipeline.
Integrate an existing message queue into an event-driven workflow.
What to do next
[Create event rules] to filter and route events from an event bus to targets.
[Explore supported event sources] for the default event bus.
[Create a custom event bus] and configure event sources for your applications.