本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。

# 因應 Amazon ECS 事件
<a name="ecs_cwet_handling"></a>

Amazon ECS 會傳送事件*至少一次*。這表示您可能會收到指定事件的多個副本。此外，可能不會依事件發生順序將事件交付至事件接聽程式。

為了正確排序事件，每個事件的 `detail` 區段都會包含 `version` 屬性。每次資源變更狀態時，此 `version` 都會遞增。重複事件在 `detail` 物件中具有相同的 `version`。如果您使用 EventBridge 複寫 Amazon ECS 容器執行個體和任務狀態，您可以將 Amazon ECS APIs 回報的資源版本與 EventBridge 中`version`回報的資源版本進行比較，以驗證事件串流中的版本是否為最新版本。較高版本屬性編號的事件應該視為比較低版本編號的事件晚發生。

## 範例：處理 AWS Lambda 函數中的事件
<a name="ecs_cwet_handling_example"></a>

下列範例顯示使用 Python 3.9 撰寫的 Lambda 函數，以同時擷取任務和容器執行個體狀態變更事件，並將其儲存至兩個 Amazon DynamoDB 資料表中的其中一個：
+ *ECSCtrInstanceState*：存放容器執行個體的最新狀態。資料表 ID 是容器執行個體的 `containerInstanceArn` 值。
+ *ECSTaskState*：存放任務的最新狀態。資料表 ID 是任務的 `taskArn` 值。

```
import json
import boto3

def lambda_handler(event, context):
    id_name = ""
    new_record = {}

    # For debugging so you can see raw event format.
    print('Here is the event:')
    print((json.dumps(event)))

    if event["source"] != "aws.ecs":
       raise ValueError("Function only supports input from events with a source type of: aws.ecs")

    # Switch on task/container events.
    table_name = ""
    if event["detail-type"] == "ECS Task State Change":
        table_name = "ECSTaskState"
        id_name = "taskArn"
        event_id = event["detail"]["taskArn"]
    elif event["detail-type"] == "ECS Container Instance State Change":
        table_name = "ECSCtrInstanceState"
        id_name =  "containerInstanceArn"
        event_id = event["detail"]["containerInstanceArn"]
    else:
        raise ValueError("detail-type for event is not a supported type. Exiting without saving event.")

    new_record["cw_version"] = event["version"]
    new_record.update(event["detail"])

    # "status" is a reserved word in DDB, but it appears in containerPort
    # state change messages.
    if "status" in event:
        new_record["current_status"] = event["status"]
        new_record.pop("status")


    # Look first to see if you have received a newer version of an event ID.
    # If the version is OLDER than what you have on file, do not process it.
    # Otherwise, update the associated record with this latest information.
    print("Looking for recent event with same ID...")
    dynamodb = boto3.resource("dynamodb", region_name="us-east-1")
    table = dynamodb.Table(table_name)
    saved_event = table.get_item(
        Key={
            id_name : event_id
        }
    )
    if "Item" in saved_event:
        # Compare events and reconcile.
        print(("EXISTING EVENT DETECTED: Id " + event_id + " - reconciling"))
        if saved_event["Item"]["version"] < event["detail"]["version"]:
            print("Received event is a more recent version than the stored event - updating")
            table.put_item(
                Item=new_record
            )
        else:
            print("Received event is an older version than the stored event - ignoring")
    else:
        print(("Saving new event - ID " + event_id))

        table.put_item(
            Item=new_record
        )
```

下列範例顯示使用 Python 3.9 撰寫的 Lambda 函式，其功能為擷取任務狀態變更事件，並將這些事件儲存至下列 Amazon DynamoDB 資料表：

```
import json
import boto3

def lambda_handler(event, context):
    id_name = ""
    new_record = {}

    # For debugging so you can see raw event format.
    print('Here is the event:')
    print((json.dumps(event)))

    if event["source"] != "aws.ecs":
       raise ValueError("Function only supports input from events with a source type of: aws.ecs")

    # Switch on task/container events.
    table_name = ""
    if event["detail-type"] == "ECS Task State Change":
        table_name = "ECSTaskState"
        id_name = "taskArn"
        event_id = event["detail"]["taskArn"]
    else:
        raise ValueError("detail-type for event is not a supported type. Exiting without saving event.")

    new_record["cw_version"] = event["version"]
    new_record.update(event["detail"])

    # "status" is a reserved word in DDB, but it appears in containerPort
    # state change messages.
    if "status" in event:
        new_record["current_status"] = event["status"]
        new_record.pop("status")


    # Look first to see if you have received a newer version of an event ID.
    # If the version is OLDER than what you have on file, do not process it.
    # Otherwise, update the associated record with this latest information.
    print("Looking for recent event with same ID...")
    dynamodb = boto3.resource("dynamodb", region_name="us-east-1")
    table = dynamodb.Table(table_name)
    saved_event = table.get_item(
        Key={
            id_name : event_id
        }
    )
    if "Item" in saved_event:
        # Compare events and reconcile.
        print(("EXISTING EVENT DETECTED: Id " + event_id + " - reconciling"))
        if saved_event["Item"]["version"] < event["detail"]["version"]:
            print("Received event is a more recent version than the stored event - updating")
            table.put_item(
                Item=new_record
            )
        else:
            print("Received event is an older version than the stored event - ignoring")
    else:
        print(("Saving new event - ID " + event_id))

        table.put_item(
            Item=new_record
        )
```