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

Amazon ECS *至少发送一次*事件。这意味着您可能会收到给定事件的多个副本。此外，无法按事件的发生顺序将事件传送到事件侦听器。

为了正确排序事件，每个事件的 `detail` 部分均包含 `version` 属性。每次当资源更改状态时，此 `version` 会递增。重复事件在 `detail` 对象中具有相同 `version`。如果使用 EventBridge 复制 Amazon ECS 容器实例和任务状态，则可以将 Amazon ECS API 报告的 `version` 资源版本与资源在 EventBridge 中报告的版本进行比较，以验证事件流中的版本是否为当前版本。版本属性数值更大的事件应视为在版本号更小的事件之后发生。

## 示例：在 Amazon Lambda 函数中处理事件
<a name="ecs_cwet_handling_example"></a>

以下示例显示了一个用 Python 3.9 编写的 Lambda 函数，此函数可同时捕获任务和容器实例状态更改事件，并将这些事件保存到两个 Amazon DynamoDB 表之一：
+ *ECSCtrInstanceState* – 存储容器实例的最新状态。表 ID 是容器实例的 `containerInstanceArn` 值。
+ *ECSTaskState* – 存储任务的最新状态。表 ID 是任务的 `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
        )
```

以下 Fargate 示例显示了一个用 Python 3.9 编写的 Lambda 函数，此函数可捕获任务状态更改事件，并将这些事件保存到以下 Amazon DynamoDB 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
        )
```