Amazon EventBridge: A Detailed Guide to Building Event-Driven Applications

6 min readAug 15, 2024

Amazon EventBridge is a serverless event bus service that enables developers to build scalable, event-driven applications. By connecting applications using data from AWS services, integrated software-as-a-service (SaaS) applications, and custom sources, EventBridge allows you to create complex workflows with minimal infrastructure management. This guide provides an in-depth look at EventBridge, covering its components, event sources, security, reliability, and practical use cases.

What is Amazon EventBridge?

Amazon EventBridge simplifies the creation of event-driven applications by allowing you to route events from various sources to targets within AWS and beyond. As a serverless service, EventBridge eliminates the need to manage servers or infrastructure, letting you focus on building your application logic. You only pay for the events you publish to your event bus, making it a cost-effective solution for event-based architectures.

Key Components of Amazon EventBridge

To effectively use EventBridge, it’s important to understand its key components:

Event: An event represents a change in state or an update within an application or service. Events are generated by producers (e.g., AWS services, SaaS applications, or custom applications) and are sent to an event bus.
Event Bus: The event bus is a channel that receives events and routes them to appropriate targets. There are default event buses that come with your AWS account, and you can create custom event buses for specific use cases.
Rule: Rules in EventBridge are used to filter incoming events based on specific criteria. A rule defines which events should be routed to which targets. You can create complex filtering patterns using the event pattern editor in the EventBridge console.
Target: Targets are the destinations where events are routed after matching a rule. Targets can be AWS services like Lambda, SNS, SQS, and Step Functions, or other systems like SaaS applications via API destinations.

Sources of Events in EventBridge

EventBridge can receive events from three primary sources:

1. AWS Services

Many AWS services are natively integrated with EventBridge, making it easy to send events to your account’s default event bus. For example, services like Amazon EC2, S3, and CloudWatch can directly publish events to EventBridge. For services that do not have direct integration, AWS CloudTrail can be used as an intermediary. CloudTrail records AWS API calls, which can then be used to trigger EventBridge rules.

When creating an event pattern for a rule in EventBridge, you can use the event-pattern form to select AWS services and event sources. The form automatically generates the required JSON format for the event pattern, which you can further customize using the JSON editor.

2. SaaS Partners

EventBridge also integrates with various SaaS applications, allowing you to receive events from third-party platforms. These events can be processed and routed just like events from AWS services. SaaS partners provide a wide range of event sources, from CRM systems to monitoring tools, which can be used to trigger workflows in your AWS environment.

3. Custom Applications

Custom applications can also publish events to EventBridge. This feature allows you to create highly customized event-driven architectures tailored to your specific business needs. By using the AWS SDKs, you can send events from your applications to an EventBridge event bus, enabling seamless integration between your custom systems and AWS services.

Invoking AWS Services with EventBridge

A common use case for EventBridge is to invoke AWS services based on specific events. For example, you might need to send events from an e-commerce application’s ordering service to a loyalty rewards program built on AWS Lambda and DynamoDB. In this scenario, you can configure EventBridge to route order-related events to Lambda functions that update the loyalty program in real-time.

Using the EventBridge console or the PutTargets API, you can easily set up rules to send events to various AWS services, enabling decoupled and scalable application architectures.

API Destinations: Expanding Beyond AWS

EventBridge supports API destinations, allowing you to send events to on-premise systems, SaaS applications, or any web-based application with an accessible HTTP endpoint. This feature is particularly useful when you need to integrate with external systems without the overhead of managing additional infrastructure or writing custom code.

An API destination consists of three components:

HTTP Endpoint: The URL of the target system or application.
HTTP Method: The HTTP method to use for the request (e.g., GET, POST, PUT).
Connection: The authorization method and credentials used to authenticate the request (e.g., basic auth, OAuth, API key).

When setting up an API destination in EventBridge, the console dynamically selects the appropriate authorization options based on the target SaaS application, simplifying the integration process.

Event Buses as Targets: Cross-Account and Cross-Region Integration

In some cases, you may need to route events between different AWS accounts or regions. EventBridge allows you to set an event bus in another account or region as the target for a rule. This capability is essential for scenarios where you need to aggregate events from multiple regions into a single location or for workloads that span multiple regions.

For example, if you have a global application that operates in several AWS regions, you can use EventBridge to centralize event processing in one region, simplifying the architecture and reducing the complexity of managing events across different regions.

Determining Optimal Event Size

When publishing events to EventBridge, knowing the payload size limits is important. The maximum size for an event payload is 256 KB. This limit includes not just the main content of the event, but also the required metadata fields like “time,” “source,” “detail-type,” and “detail.” Event size is calculated when the event is received by the PutEvents API call, so it’s essential to optimize your event structure to stay within this limit.

Security in Amazon EventBridge

Security is a critical aspect of any event-driven architecture. In EventBridge, access to resources is controlled through AWS Identity and Access Management (IAM). IAM allows you to define policies that specify what actions an entity (user, service, or application) is allowed to perform within your AWS account.

EventBridge operates under the AWS shared responsibility model. AWS is responsible for securing the underlying infrastructure, while you are responsible for configuring your EventBridge resources securely. This includes setting up IAM policies, ensuring that sensitive data is encrypted, and monitoring access to your event buses.

Reliability of Event Delivery: Handling Failures

Event-driven architectures depend on reliable event delivery. However, there are situations where an event might not be delivered, such as when a target is unavailable, EventBridge lacks the necessary permissions, or there is a networking issue. To ensure that events are not lost, EventBridge is designed to provide at least once event delivery to targets.

When configuring EventBridge rules, you can define a retry policy that specifies how long EventBridge should attempt to deliver an event and how many retries should be made. The default retry policy in EventBridge will retry delivery for 24 hours with up to 185 attempts, using exponential back-off and jitter (randomized delays) to avoid overwhelming the system or network.

If the retries are unsuccessful, the event is dropped. To prevent losing important events, you can configure a dead-letter queue (DLQ), where failed events are sent for later analysis or reprocessing.

Practical Use Cases for Amazon EventBridge

Here are a few examples of how you can use Amazon EventBridge to create powerful event-driven applications:

Real-Time Data Processing: Use EventBridge to route events from IoT devices or data streams to AWS Lambda functions for real-time processing and analytics.
Cross-Account Automation: Automatically trigger workflows in multiple AWS accounts by routing events from one account’s event bus to another.
Incident Management: Integrate with monitoring tools like Datadog or PagerDuty via SaaS partner events to automatically escalate incidents based on specific triggers.
Custom Notifications: Send customized notifications or alerts based on specific events in your application, integrating with services like Amazon SNS or third-party communication tools.

Conclusion

Amazon EventBridge is a versatile and powerful service that simplifies the development of event-driven applications. With its serverless architecture, seamless integration with AWS services and SaaS applications, and robust security and reliability features, EventBridge is an essential tool for modern cloud-native architectures.

By understanding the key components, event sources, and best practices for using EventBridge, you can design and implement scalable, resilient, and secure event-driven systems that meet your organization’s needs.