Event bus concepts in Amazon EventBridge

Here's a closer look at the main components of an event driven architecture built on event buses.

Event buses

An event bus is a router that receives events and delivers them to zero or more destinations,or targets. Use an event bus when you need to route events from many sources to many targets, with optional transformation of events prior to delivery to a target.

Your account includes a default event bus that automatically receives events from AWS services. You can also:

• Create additional event buses, called custom event buses, and specify which events they receive.

• Create partner event buses, which receive events from SaaS partners.

Common use cases for event buses include:

• Using an event bus as a broker between different workloads, services, or systems.

• Using multiple event buses in your applications to divide up the event traffic. For example, creating a bus to process events containing personal identification information (PII), and another bus for events that don't.

• Aggregating events by sending events from multiple event buses to a centralized event bus. This centralized bus can be in the same account as the other buses, but can also be in a different account or Region.

Events

At its simplest, an EventBridge event is a JSON object sent to an event bus or pipe.

In the context of event-driven architecture (EDA), an event often represents an indicator of a change in a resource or environment.

For more information, see Events in Amazon EventBridge.

Event sources

EventBridge can receive events from event sources including:

• AWS services

• Custom applications

• Software as a service (SaaS) partners

Rules

A rule receives incoming events and sends them as appropriate to targets for processing. You can specify how each rule invokes their target(s) based on either:

• An event pattern, which contains one or more filters to match events. Event patterns can include filters that match on:

  • Event metadata – Data about the event, such as the event source, or the account or Region in which the event originated.

  • Event data – The properties of the event itself. These properties vary according to event.

  • Event content – The actual property values of the event data.

• A schedule to invoke the target(s) at regular intervals.

  You can specify a scheduled rule within EventBridge, or by using EventBridge Scheduler.

  Note

  While you can create rules that run on a schedule, EventBridge now offers a more flexible and powerful way to create, run, and manage scheduled tasks centrally: EventBridge Scheduler. With EventBridge Scheduler, you can create schedules using cron and rate expressions for recurring patterns, or configure one-time invocations. You can set up flexible time windows for delivery, define retry limits, and set the maximum retention time for failed API invocations.

  Scheduler is highly customizable, and offers improved scalability over scheduled rules, with a wider set of target API operations and AWS services. We recommend that you use Scheduler to invoke targets on a schedule.

  For more information, see Create a schedule.

Each rule is defined for a specific event bus, and only apply to events on that event bus.

A single rule can send an event to up to five targets.

By default, you can configure up to 300 rules per event bus. This quota can be raised to thousands of rules in the Service Quotas console. Since the rule limit apply to each bus, if you require even more rules, you can create additional custom event buses in your account.

You can customize how events are received in your account by creating event buses with different permissions for different services.

To customize the structure or date of an event before EventBridge passes it to a target, use the input transformer to edit the information before it goes to the target.

For more information, see Rules in Amazon EventBridge.

Targets

A target is a resource or endpoint to which EventBridge sends an event when the event matches the event pattern defined for a rule.

A target can receive multiple events from multiple event buses.

For more information, see Event bus targets in Amazon EventBridge .

Advanced features for event buses

EventBridge includes the following features to help you develop, manage, and use event buses.

Using API destinations to enable REST API calls between services

EventBridge API destinations are HTTP endpoints that you can set as the target of a rule, in the same way that you would send event data to an AWS service or resource. By using API destinations, you can use API calls to route events between AWS services, integrated SaaS applications, and your applications outside of AWS. When you create an API destination, you specify a connection to use for it. Each connection includes the details about the authorization type and parameters to use to authorize with the API destination endpoint.

Archiving and replaying events to aid development and disaster recovery

You can archive, or save, events and then replay them at a later time from the archive. Archiving is useful for:

• Testing an application because you have a store of events to use rather than having to wait for new events.

• Hydrating a new service when it first comes online.

• Adding more durability to your event-driven applications.

Using the Schema Registry to jump-start event pattern creation

When you build serverless applications that use EventBridge, it can be helpful to know the structure of typical events without having to generate the event. The event structure are described in schemas, which are available for all events generated by AWS services on EventBridge.

For events that don't come from AWS services, you can:

• Create or upload custom schemas.

• Use Schema Discovery to have EventBridge automatically create schemas for events sent to the event bus.

Once you have a schema for an event, you can download code bindings for popular programming languages.

Managing resources and access with policies

To organize AWS resources or to track costs in EventBridge, you can assign a custom label, or tag, to AWS resources. Using tag-based policies, you can control what resources can and can’t do within EventBridge.

In addition to tag-based policies, EventBridge supports identity-based and resource-based policies to control access to EventBridge. Use identity-based policies to control the permissions of a group, role, or user. Use resource-based policies to give specific permissions to each resource, such as a Lambda function or Amazon SNS topic.