Eventbridge

Core Concepts

Event Bus

Channel that receives events. Types:

• Default: Receives AWS service events
• Custom: Your application events
• Partner: SaaS application events

Rules

Match incoming events and route to targets. Each rule can have up to 5 targets.

Event Patterns

JSON patterns that define which events match a rule.

Targets

AWS services that receive matched events (Lambda, SQS, SNS, Step Functions, etc.).

Scheduler

Schedule one-time or recurring events to invoke targets.

Common Patterns

Create Custom Event Bus and Rule

AWS CLI:

# Create custom event bus
aws events create-event-bus --name my-app-events

# Create rule
aws events put-rule \
  --name order-created-rule \
  --event-bus-name my-app-events \
  --event-pattern '{
    "source": ["my-app.orders"],
    "detail-type": ["Order Created"]
  }'

# Add Lambda target
aws events put-targets \
  --rule order-created-rule \
  --event-bus-name my-app-events \
  --targets '[{
    "Id": "process-order",
    "Arn": "arn:aws:lambda:us-east-1:123456789012:function:ProcessOrder"
  }]'

# Add Lambda permission
aws lambda add-permission \
  --function-name ProcessOrder \
  --statement-id eventbridge-order-created \
  --action lambda:InvokeFunction \
  --principal events.amazonaws.com \
  --source-arn arn:aws:events:us-east-1:123456789012:rule/my-app-events/order-created-rule

boto3:

import boto3

events = boto3.client('events')

# Create event bus
events.create_event_bus(Name='my-app-events')

# Create rule
events.put_rule(
    Name='order-created-rule',
    EventBusName='my-app-events',
    EventPattern=json.dumps({
        'source': ['my-app.orders'],
        'detail-type': ['Order Created']
    }),
    State='ENABLED'
)

# Add target
events.put_targets(
    Rule='order-created-rule',
    EventBusName='my-app-events',
    Targets=[{
        'Id': 'process-order',
        'Arn': 'arn:aws:lambda:us-east-1:123456789012:function:ProcessOrder'
    }]
)

Publish Custom Events

import boto3
import json

events = boto3.client('events')

events.put_events(
    Entries=[
        {
            'Source': 'my-app.orders',
            'DetailType': 'Order Created',
            'Detail': json.dumps({
                'order_id': '12345',
                'customer_id': 'cust-789',
                'total': 99.99,
                'items': [
                    {'product_id': 'prod-1', 'quantity': 2}
                ]
            }),
            'EventBusName': 'my-app-events'
        }
    ]
)

Scheduled Events

# Run every 5 minutes
aws events put-rule \
  --name every-5-minutes \
  --schedule-expression "rate(5 minutes)"

# Run at specific times (cron)
aws events put-rule \
  --name daily-cleanup \
  --schedule-expression "cron(0 2 * * ? *)"

# Add target
aws events put-targets \
  --rule every-5-minutes \
  --targets '[{
    "Id": "cleanup-function",
    "Arn": "arn:aws:lambda:us-east-1:123456789012:function:Cleanup"
  }]'

EventBridge Scheduler (One-Time and Flexible)

# One-time schedule
aws scheduler create-schedule \
  --name send-reminder \
  --schedule-expression "at(2024-12-25T09:00:00)" \
  --target '{
    "Arn": "arn:aws:lambda:us-east-1:123456789012:function:SendReminder",
    "RoleArn": "arn:aws:iam::123456789012:role/scheduler-role",
    "Input": "{\"message\": \"Merry Christmas!\"}"
  }' \
  --flexible-time-window '{"Mode": "OFF"}'

# Recurring with flexible window
aws scheduler create-schedule \
  --name hourly-sync \
  --schedule-expression "rate(1 hour)" \
  --target '{
    "Arn": "arn:aws:lambda:us-east-1:123456789012:function:SyncData",
    "RoleArn": "arn:aws:iam::123456789012:role/scheduler-role"
  }' \
  --flexible-time-window '{"Mode": "FLEXIBLE", "MaximumWindowInMinutes": 15}'

AWS Service Events

# EC2 state changes
aws events put-rule \
  --name ec2-state-change \
  --event-pattern '{
    "source": ["aws.ec2"],
    "detail-type": ["EC2 Instance State-change Notification"],
    "detail": {
      "state": ["stopped", "terminated"]
    }
  }'

# S3 object created
aws events put-rule \
  --name s3-upload \
  --event-pattern '{
    "source": ["aws.s3"],
    "detail-type": ["Object Created"],
    "detail": {
      "bucket": {"name": ["my-bucket"]},
      "object": {"key": [{"prefix": "uploads/"}]}
    }
  }'

CLI Reference

Event Buses

Rules

Targets

Events

Best Practices

Event Design

• Use meaningful source names — company.service.component
• Use descriptive detail-types — Order Created, User Signed Up
• Include correlation IDs for tracing
• Keep events small (< 256 KB)
• Use versioning for event schemas

# Good event structure
{
    'Source': 'mycompany.orders.api',
    'DetailType': 'Order Created',
    'Detail': json.dumps({
        'version': '1.0',
        'correlation_id': 'req-abc-123',
        'timestamp': '2024-01-15T10:30:00Z',
        'order_id': '12345',
        'data': {...}
    })
}

Reliability

• Use DLQs for failed deliveries
• Implement idempotency in consumers
• Monitor failed invocations
• Use archive and replay for recovery

Security

• Use resource policies to control access
• Enable encryption with KMS
• Use IAM roles for targets

Cost Optimization

• Use specific event patterns to reduce matches
• Batch events when publishing (up to 10 per call)
• Archive selectively — not all events

Troubleshooting

Rule Not Triggering

Debug:

# Check rule status
aws events describe-rule --name my-rule

# Check targets
aws events list-targets-by-rule --rule my-rule

# Test event pattern
aws events test-event-pattern \
  --event-pattern '{"source": ["my-app"]}' \
  --event '{"source": "my-app", "detail-type": "Test"}'

Common causes:

• Rule disabled
• Event pattern doesn't match
• Target permissions missing

Lambda Not Invoked

Check Lambda permissions:

aws lambda get-policy --function-name MyFunction

Required permission:

{
  "Principal": "events.amazonaws.com",
  "Action": "lambda:InvokeFunction",
  "Resource": "function-arn",
  "Condition": {
    "ArnLike": {
      "AWS:SourceArn": "rule-arn"
    }
  }
}

Events Not Reaching Custom Bus

Check:

• Publishing to correct bus name
• Event format is valid JSON
• Put events has proper permissions

# Test publish
aws events put-events \
  --entries '[{
    "Source": "test",
    "DetailType": "Test Event",
    "Detail": "{}",
    "EventBusName": "my-app-events"
  }]'

Viewing Failed Events

# Enable CloudWatch metrics
aws events put-rule \
  --name my-rule \
  --event-pattern '...' \
  --state ENABLED

# Check FailedInvocations metric
aws cloudwatch get-metric-statistics \
  --namespace AWS/Events \
  --metric-name FailedInvocations \
  --dimensions Name=RuleName,Value=my-rule \
  --start-time $(date -d '1 hour ago' -u +%Y-%m-%dT%H:%M:%SZ) \
  --end-time $(date -u +%Y-%m-%dT%H:%M:%SZ) \
  --period 300 \
  --statistics Sum

References

• EventBridge User Guide
• EventBridge API Reference
• EventBridge CLI Reference
• boto3 EventBridge
• Event Pattern Reference