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。

# 回應 Amazon EMR 叢集執行個體容量不足事件
<a name="emr-events-response-insuff-capacity"></a>

## 概觀
<a name="emr-events-response-insuff-capacity-overview"></a>

當選取的可用區域沒有足夠的容量來滿足叢集啟動或調整大小請求時，Amazon EMR 叢集會傳回事件代碼 `EC2 provisioning - Insufficient Instance Capacity`。如果 Amazon EMR 重複發生容量不足的例外狀況，且無法滿足叢集啟動或叢集調整大小操作的佈建請求，則事件會與執行個體群組和執行個體機群一起定期發出。

本頁描述了在 EMR 叢集發生此事件類型時，如何對其做出最佳回應。

## 容量不足事件的建議回應
<a name="emr-events-response-insuff-capacity-rec"></a>

建議您使用下列其中一種方式回應容量不足事件：
+ 等待容量恢復。容量經常變化，因此容量不足例外狀況可以自行恢復。一旦 Amazon EC2 容量變得可用，叢集就會開始或完成調整大小。
+ 或者，也可終止叢集，修改執行個體類型組態，以及使用更新後的叢集組態請求建立新叢集。如需詳細資訊，請參閱[Amazon EMR 叢集的可用區域彈性](emr-flexibility.md)。

也可以為容量不足事件設定規則或自動回應，如下一節所述。

## 從容量不足事件中自動復原
<a name="emr-events-response-insuff-capacity-ex"></a>

可以建置自動化來回應 Amazon EMR 事件，例如具有事件代碼 `EC2 provisioning - Insufficient Instance Capacity` 的事件。例如，下列 AWS Lambda 函數會終止具有使用隨需執行個體之執行個體群組的 EMR 叢集，然後使用包含與原始請求不同執行個體類型的執行個體群組建立新的 EMR 叢集。

下列情況會觸發自動化程序：
+ 主要節點或核心節點的容量不足事件已經發出超過 20 分鐘。
+ 叢集不處於**就緒**或**等待中**狀態。如需有關 EMR 叢集狀態的詳細資訊，請參閱 [了解叢集生命週期](emr-overview.md#emr-overview-cluster-lifecycle)。

**注意**  
當您針對容量不足例外狀況建置自動化程序時，應考慮容量不足事件可復原。容量通常會變化，而且叢集會在 Amazon EC2 容量變得可用後立即繼續調整大小或開始操作。

**Example 回應容量不足事件的函數**  

```
// Lambda code with Python 3.10 and handler is lambda_function.lambda_handler
// Note: related IAM role requires permission to use Amazon EMR

import json
import boto3
import datetime
from datetime import timezone

INSUFFICIENT_CAPACITY_EXCEPTION_DETAIL_TYPE = "EMR Instance Group Provisioning"
INSUFFICIENT_CAPACITY_EXCEPTION_EVENT_CODE = (
    "EC2 provisioning - Insufficient Instance Capacity"
)
ALLOWED_INSTANCE_TYPES_TO_USE = [
    "m5.xlarge",
    "c5.xlarge",
    "m5.4xlarge",
    "m5.2xlarge",
    "t3.xlarge",
]
CLUSTER_START_ACCEPTABLE_STATES = ["WAITING", "RUNNING"]
CLUSTER_START_SLA = 20

CLIENT = boto3.client("emr", region_name="us-east-1")

# checks if the incoming event is 'EMR Instance Fleet Provisioning' with eventCode 'EC2 provisioning - Insufficient Instance Capacity'
def is_insufficient_capacity_event(event):
    if not event["detail"]:
        return False
    else:
        return (
            event["detail-type"] == INSUFFICIENT_CAPACITY_EXCEPTION_DETAIL_TYPE
            and event["detail"]["eventCode"]
            == INSUFFICIENT_CAPACITY_EXCEPTION_EVENT_CODE
        )


# checks if the cluster is eligible for termination
def is_cluster_eligible_for_termination(event, describeClusterResponse):
    # instanceGroupType could be CORE, MASTER OR TASK
    instanceGroupType = event["detail"]["instanceGroupType"]
    clusterCreationTime = describeClusterResponse["Cluster"]["Status"]["Timeline"][
        "CreationDateTime"
    ]
    clusterState = describeClusterResponse["Cluster"]["Status"]["State"]

    now = datetime.datetime.now()
    now = now.replace(tzinfo=timezone.utc)
    isClusterStartSlaBreached = clusterCreationTime < now - datetime.timedelta(
        minutes=CLUSTER_START_SLA
    )

    # Check if instance group receiving Insufficient capacity exception is CORE or PRIMARY (MASTER),
    # and it's been more than 20 minutes since cluster was created but the cluster state and the cluster state is not updated to RUNNING or WAITING
    if (
        (instanceGroupType == "CORE" or instanceGroupType == "MASTER")
        and isClusterStartSlaBreached
        and clusterState not in CLUSTER_START_ACCEPTABLE_STATES
    ):
        return True
    else:
        return False


# Choose item from the list except the exempt value
def choice_excluding(exempt):
    for i in ALLOWED_INSTANCE_TYPES_TO_USE:
        if i != exempt:
            return i


# Create a new cluster by choosing different InstanceType.
def create_cluster(event):
    # instanceGroupType cloud be CORE, MASTER OR TASK
    instanceGroupType = event["detail"]["instanceGroupType"]

    # Following two lines assumes that the customer that created the cluster already knows which instance types they use in original request
    instanceTypesFromOriginalRequestMaster = "m5.xlarge"
    instanceTypesFromOriginalRequestCore = "m5.xlarge"

    # Select new instance types to include in the new createCluster request
    instanceTypeForMaster = (
        instanceTypesFromOriginalRequestMaster
        if instanceGroupType != "MASTER"
        else choice_excluding(instanceTypesFromOriginalRequestMaster)
    )
    instanceTypeForCore = (
        instanceTypesFromOriginalRequestCore
        if instanceGroupType != "CORE"
        else choice_excluding(instanceTypesFromOriginalRequestCore)
    )

    print("Starting to create cluster...")
    instances = {
        "InstanceGroups": [
            {
                "InstanceRole": "MASTER",
                "InstanceCount": 1,
                "InstanceType": instanceTypeForMaster,
                "Market": "ON_DEMAND",
                "Name": "Master",
            },
            {
                "InstanceRole": "CORE",
                "InstanceCount": 1,
                "InstanceType": instanceTypeForCore,
                "Market": "ON_DEMAND",
                "Name": "Core",
            },
        ]
    }
    response = CLIENT.run_job_flow(
        Name="Test Cluster",
        Instances=instances,
        VisibleToAllUsers=True,
        JobFlowRole="EMR_EC2_DefaultRole",
        ServiceRole="EMR_DefaultRole",
        ReleaseLabel="emr-6.10.0",
    )

    return response["JobFlowId"]


# Terminated the cluster using clusterId received in an event
def terminate_cluster(event):
    print("Trying to terminate cluster, clusterId: " + event["detail"]["clusterId"])
    response = CLIENT.terminate_job_flows(JobFlowIds=[event["detail"]["clusterId"]])
    print(f"Terminate cluster response: {response}")


def describe_cluster(event):
    response = CLIENT.describe_cluster(ClusterId=event["detail"]["clusterId"])
    return response


def lambda_handler(event, context):
    if is_insufficient_capacity_event(event):
        print(
            "Received insufficient capacity event for instanceGroup, clusterId: "
            + event["detail"]["clusterId"]
        )

        describeClusterResponse = describe_cluster(event)

        shouldTerminateCluster = is_cluster_eligible_for_termination(
            event, describeClusterResponse
        )
        if shouldTerminateCluster:
            terminate_cluster(event)

            clusterId = create_cluster(event)
            print("Created a new cluster, clusterId: " + clusterId)
        else:
            print(
                "Cluster is not eligible for termination, clusterId: "
                + event["detail"]["clusterId"]
            )

    else:
        print("Received event is not insufficient capacity event, skipping")
```