[AWS] EventBridge

Amazon EventBridge is a serverless event bus service that makes it easy to connect your applications with data from a variety of sources. It helps you to build event-driven architectures that are loosely coupled and distributed.

Serverless Event Router – Amazon EventBridge – Amazon Web Services

Features

• EventBridge delivers a stream of real-time data from your applications or AWS services and routes that data to targets such as AWS Lambda using the routing rules.
• EventBridge is the updated version of CloudWatch Events.

Schema Registry

• Schema of an events can be inferred.
• Schema can be versioned.

Components

Events

• Changes in your resources and sent to EventBridge
• Event Structure
  • source
  • detail
  • detail-type

{
  "version": "0",
  "id": "ac51d123-45e1-460a-a1fa-e15d188c17e1",
  "detail-type": "EC2 Instance State-change Notification",
  "source": "aws.ec2",
  "account": "123456789101",
  "time": "2022-12-25T13:11:28Z",
  "region": "us-east-1",
  "resources": [
    "arn:aws:ec2:us-east-1:123456789101:instance/i-1234567890abcdef0"
  ],
  "detail": {
    "instance-id": "i-1234567890abcdef0",
    "state": "stopped"
  }
}

Destinations

• Targets
  • Resources or endpoints to which EventBridge sends events after matching a rule
• You can configure up to 5 destinations per rule.
• JSON data will be sent to the destination.

Rules

• Rules are the glue in the pipeline.
• A Rule matches an event and sends it to its designated (single or multiple) targets.
• Events can be matched to rules by:
  • Rate-based or cron-based schedule
  • Event pattern matching
    • prefix/suffix matching

# example 1 
# matching rule - state is "stopping" or "stopped"

{
  "source": ["aws.ec2"],
  "detail-type": ["EC2 Instance State-change Notification"],
  "detail": {
    "state": ["stopping", "stopped"]
  }
}

# example 2
# matching rule - S3 Object Create event
# prefix, suffix, ip matching

{
  "source": ["aws.s3"],
  "detail-type": "Object Created",
  "detail": {
    "bucket": {
      "name": : [ { "prefix", "mybucket" }]
    },
    "object": {
      "key": : [ { "suffix", ".jpg" }]
    },
    "source-ip-address": : [ { "cidr", "10.0.0.0/24" }] 
  }
}

Replay

• Events are saved (archived), and we can replay them later

Event Bus

• “Event Bus” is a serverless pipeline that can deliver events from different sources.
• Every account has a default event bus.
  • The default event bus is used for the events from AWS services.
• You can create a custom event bus for custom applications.
• “Rules” are associated with buses and are applied when matching events arrive.
  • There is a limit: 300 rules per event bus!

Input Transformation

• You can transform input data to another using the transformation document.
• You can refer the values in the input data using “$“

{
  "type": "$.detail.type"
  "time-stamp": "$.time",
  "instance": "$.detail.instance-id",
  "state": "$.detail.state",
  "resource": "$.detail.resources[0]"
}

Security

Resource-based Policy

• You can define which event can be allowed or denied to a specific event bus.
• Use cases
  • aggregate all events from the accounts in your AWS Organization in a single account (single region)

"Statement": [
  {
    "Effect": "Allow"
    "Action": "events:PutEvents",
    "Principal": { "AWS:<account>" },
    "Resource": "arn:aws:events:<region>:<central-account>:event-bus:<bus-name>"
  }
]

Working with Lambda

• EventBridge can invoke Lambda functions asynchronously.