Amazon EventBridge
Event routing
An event bus: receives events from AWS services, SaaS and applications, filters them with rules and routes them to targets (Lambda, Step Functions, SQS…); also runs schedules.
- Cost$ Low
- Difficulty●●●●●
- Costs money when idle?No
- Serverless
- In examsSAA · DVA · SOA
Think of it asLike a mail sorting center: reads the content and forwards it to the right department.
Where does EventBridge fit?
EventBridgeEventBridge calls
A real example, step by step
- You want the ops team to know immediately whenever a production EC2 instance stops, and to log an incident automatically.
- EC2 already publishes state-change events to EventBridge's default event bus; nothing to install.
- You create a rule: state = stopped with tag env=prod goes to a Lambda that logs the incident and to SNS to alert the team.
- You also use EventBridge Scheduler to run the cost report at 8 a.m. every Monday instead of keeping a cron server.
- Later, the SaaS payment system starts sending events to EventBridge too, and you just add a new rule.
When to use it
✓ Use it when
Event-driven architecture, reacting to changes in your AWS account, running cron jobs.
✗ Avoid it when
Continuous data streams that need ordered replay → Kinesis.
Common uses
- React to changes in your AWS account (EC2 stopped, new file…)
- Event-driven architecture between microservices
- Scheduled runs (Scheduler)
- Receive events from SaaS (Shopify, Zendesk…)
EventBridge, SNS or SQS?
| EventBridge |  SNS |  SQS | |
|---|---|---|---|
| Type | Routes events by content | Pub/sub to many subscribers | Queue waiting to be processed |
| Event sources | AWS services, SaaS, your apps | Apps that publish | Apps that send |
| Filtering | Rich rule patterns | By attributes | None |
| Extras | Archive and replay, scheduling | SMS, email, mobile push | Keeps messages up to 14 days |
What does it cost?
- Pricing model: Events from AWS services: free. Custom/SaaS events ~$1/1 million; Scheduler ~$1/1 million invocations; Pipes and replay billed separately.
- Free tier: Scheduler: 14 million invocations/month free.
Overly broad rules causing event loops; archives keeping events forever.
React automatically to AWS service events (an instance changing state, a GuardDuty finding) → an EventBridge rule. Run on a schedule without a cron server → EventBridge Scheduler. Its old name in exam questions: CloudWatch Events.
Try real exam questions
1A company's web application consists of multiple Amazon EC2 instances that run behind an Application Load Balancer in a VPC. An Amazon RDS for MySQL DB instance contains the data. The company needs the ability to automatically detect and respond to suspicious or unexpected behavior in its AWS environment. The company already has added AWS WAF to its architecture. What should a solutions architect do next to protect against threats?
- AUse Amazon GuardDuty to perform threat detection. Configure Amazon EventBridge (Amazon CloudWatch Events) to filter for GuardDuty findings and to invoke an AWS Lambda function to adjust the AWS WAF rules.
- BUse AWS Firewall Manager to perform threat detection. Configure Amazon EventBridge (Amazon CloudWatch Events) to filter for Firewall Manager findings and to invoke an AWS Lambda function to adjust the AWS WAF web ACL.
- CUse Amazon Inspector to perform threat detection and to update the AWS WAF rules. Create a VPC network ACL to limit access to the web application.
- DUse Amazon Macie to perform threat detection and to update the AWS WAF rules. Create a VPC network ACL to limit access to the web application.
Show answer
Correct answer: A
GuardDuty detects suspicious behavior; EventBridge catches its findings and invokes Lambda to update the WAF rules automatically. Inspector scans software vulnerabilities and Macie finds sensitive data; neither is a threat detector.
Frequently asked questions
What is EventBridge Scheduler for?
Running tasks on a schedule (cron or a one-time date and time) and calling hundreds of AWS APIs directly, instead of keeping a separate server for cron jobs. It supports time zones and millions of schedules.
How is EventBridge priced?
Events from AWS services on the default event bus are free. You pay for custom and SaaS events published, and for archive, replay, Pipes and Scheduler based on usage.
What do AWS exams ask about EventBridge?
Reacting automatically to AWS service events (for example, invoking Lambda when an instance changes state), scheduled tasks, sending events to another account, and choosing between EventBridge, SNS and SQS.