# Amazon EventBridge 簡介

###### tags: `AWS`,`EventBridge`

## 簡介
- Serverless Event Router


## EventBridge 架構
根據 **Event Patterns** 設定的規則，Event 中特定的參數將會被 Event Bus 送往特定的目的地

digraph hierarchy {

                nodesep=1.0 // increases the separation between nodes

                node [color=Red,fontname=Courier,shape=box] //All nodes will this shape and colour
                edge [color=Blue, style=dashed] //All the lines look like this

                Event->{EventBus}
                EventBus->{ExportLambda, TransactionLambda, XXXLambda}
}

### Event Patterns
- `source`, `detail-type`, `detail` 組成，設定 Rule 將符合 Patterns 的 evnet 指定特定目的地，event bus 將會根據 Rule 發送

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

Event:

{
  "version": "0",
  "id": "6a7e8feb-b491-4cf7-a9f1-bf3703467718",
  "detail-type": "EC2 Instance State-change Notification",
  "source": "aws.ec2",
  "account": "111122223333",
  "time": "2017-12-22T18:43:48Z",
  "region": "us-west-1",
  "resources": [
    "arn:aws:ec2:us-west-1:123456789012:instance/i-1234567890abcdef0"
  ],
  "detail": {
    "instance-id": "i-1234567890abcdef0",
    "state": "terminated"
  }
}

- [Best practices](https://docs.aws.amazon.com/eventbridge/latest/userguide/eb-patterns-best-practices.html)

### Event retry policy
若未成功傳送至 target 時，EventBridge 預設在 24 hr 內重新發送，最多重送 185 次，重送間隔參考[ exponential back off and jitter](https://aws.amazon.com/tw/blogs/architecture/exponential-backoff-and-jitter/)，若仍失敗，event 將被丟棄

如果是很重要的 event，可設定 DLQ(dead-letter queue) 來收集被丟棄的 event

### Quotas
- 每個帳號預設可建 100 個 event buses
- 每個 event bus rule 上限預設 300
- event pattern 預設最多 2048 characters
- event 內容最多 256KB
- PutEvents API 每秒的最大請求數
- 東京(ap-northeast-1): 1200
- 新加坡(ap-southeast-1): 1200
- 其他可參考 [EventBridge quotas](https://docs.aws.amazon.com/eventbridge/latest/userguide/eb-quota.html)

## EventBridge V.S. Queue
Queue 也可以做到類似 EventBridge 的效果，差異在於 EventBridge 是依據設定的 Patterns 作分流，分流部分由 EventBridge 完成。而 Queue 必須自行實作這部分，下面例子是 Queue 會 Trigger 自行實作的 RouterLambda，RouterLambda 再根據 Event 參數做分流：

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                nodesep=1.0 // increases the separation between nodes

                node [color=Red,fontname=Courier,shape=box] //All nodes will this shape and colour
                edge [color=Blue, style=dashed] //All the lines look like this

                Event->{Queue}
                Queue->{RouterLambda}
                RouterLambda->{ExportLambda, TransactionLambda, XXXLambda}
}