EventBridge

AWS EventBridge is a serverless event bus service that allows you to connect applications using events. It's basically a highly scalable and flexible way to route events between AWS services, custom applications, and even external SaaS services.

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🔧 What is EventBridge used for?

• Decoupling services via event-driven architecture

• Automating workflows based on events (e.g., an S3 file upload triggers a Lambda)

• Integrating SaaS apps like Zendesk, Datadog, etc., with your AWS services

• Creating custom application events and routing them based on rules

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🧠 Core Concepts

Component	Description
Event Bus	A pipeline that receives and routes events. AWS has default buses, or you can create custom ones.
Event	A JSON object representing a change or action (e.g., EC2 state change).
Rule	Determines which events trigger which targets based on pattern matching.
Target	The service to invoke (e.g., Lambda, SQS, SNS, Step Functions).
Schema Registry	Helps discover, create, and manage event schemas. Useful for codegen.

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🚀 Example Use Case

You want to trigger a Lambda function whenever an EC2 instance is terminated:

1. Source: EC2 (AWS service event)

2. Event Bus: default

3. Rule: Match event where detail.state is "terminated"

4. Target: Your Lambda function

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🔗 Integration Targets

• AWS Lambda

• SNS / SQS

• Step Functions

• ECS Tasks

• Kinesis streams

• CodeBuild

• And more...

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✅ Features

• Schema discovery

• Event replay

• Event archiving

• Cross-account event routing

• SaaS integrations

• Reliable delivery with retries and DLQ (dead-letter queue)

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Perfect! Here's a hands-on demo workflow using AWS EventBridge + Lambda — super useful if you're learning event-driven architectures.

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🎯 Goal

Trigger a Lambda function whenever a file is uploaded to an S3 bucket using EventBridge.

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🧱 Architecture Diagram

[S3 Upload] ---> [EventBridge Rule] ---> [Lambda Function]

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⚙️ Step-by-Step Workflow

✅ Step 1: Create an S3 Bucket

aws s3 mb s3://my-eventbridge-demo-bucket

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✅ Step 2: Create a Lambda Function

Example function code (index.js):

exports.handler = async (event) => {
  console.log("Event received:", JSON.stringify(event, null, 2));
  return {
    statusCode: 200,
    body: "File upload detected!",
  };
};

Create the Lambda:

zip function.zip index.js

aws lambda create-function \
  --function-name S3UploadHandler \
  --runtime nodejs18.x \
  --handler index.handler \
  --zip-file fileb://function.zip \
  --role arn:aws:iam::123456789012:role/lambda-exec-role

Ensure the IAM role has AWSLambdaBasicExecutionRole and permissions for EventBridge

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✅ Step 3: Create an EventBridge Rule

This rule triggers on S3 object upload events:

aws events put-rule \
  --name S3UploadRule \
  --event-pattern '{
    "source": ["aws.s3"],
    "detail-type": ["Object Created"],
    "resources": ["arn:aws:s3:::my-eventbridge-demo-bucket"]
  }'

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✅ Step 4: Add Lambda as a Target

aws events put-targets \
  --rule S3UploadRule \
  --targets '[
    {
      "Id": "TargetLambda",
      "Arn": "arn:aws:lambda:us-east-1:123456789012:function:S3UploadHandler"
    }
  ]'

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✅ Step 5: Grant EventBridge permission to invoke Lambda

aws lambda add-permission \
  --function-name S3UploadHandler \
  --statement-id S3EventBridgeInvoke \
  --action 'lambda:InvokeFunction' \
  --principal events.amazonaws.com \
  --source-arn arn:aws:events:us-east-1:123456789012:rule/S3UploadRule

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✅ Step 6: Test It!

Upload a file to your bucket:

aws s3 cp myfile.txt s3://my-eventbridge-demo-bucket/

Check CloudWatch Logs for your Lambda to confirm it ran!

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🧠 Extra Tips

• Use Dead Letter Queues (DLQ) for handling failed invocations

• Use Event Replay if needed (requires enabling event archiving)

• You can also use custom events with your own app or microservices

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