Azure 元数据服务：适用于 Linux VM 的计划事件Azure Metadata Service: Scheduled Events for Linux VMs

• 11/11/2020
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计划事件是一个 Azure 元数据服务，可提供应用程序时间用于准备虚拟机 (VM) 维护。Scheduled Events is an Azure Metadata Service that gives your application time to prepare for virtual machine (VM) maintenance. 它提供有关即将发生的维护事件的信息（例如重新启动），使应用程序可以为其准备并限制中断。It provides information about upcoming maintenance events (for example, reboot) so that your application can prepare for them and limit disruption. 它可用于 Windows 和 Linux 上的所有 Azure 虚拟机类型（包括 PaaS 和 IaaS）。It's available for all Azure Virtual Machines types, including PaaS and IaaS on both Windows and Linux.

有关 Windows 上的计划事件的信息，请参阅适用于 Windows VM 的计划事件。For information about Scheduled Events on Windows, see Scheduled Events for Windows VMs.

为何使用计划事件？Why use Scheduled Events?

许多应用程序都可以受益于时间来准备 VM 维护。Many applications can benefit from time to prepare for VM maintenance. 时间可以用于执行应用程序的特定任务的提高可用性、可靠性和可维护性，包括：The time can be used to perform application-specific tasks that improve availability, reliability, and serviceability, including:

• 检查点和还原。Checkpoint and restore.
• 连接清空。Connection draining.
• 主要副本故障转移。Primary replica failover.
• 从负载均衡器池删除。Removal from a load balancer pool.
• 事件日志记录。Event logging.
• 正常关闭。Graceful shutdown.

使用计划事件，应用程序可以发现维护的发生，并触发任务以限制其影响。With Scheduled Events, your application can discover when maintenance will occur and trigger tasks to limit its impact.

预定事件提供以下用例中的事件：Scheduled Events provides events in the following use cases:

• 平台启动的维护（例如，VM 重新启动、实时迁移或主机的内存保留更新）Platform initiated maintenance (for example, VM reboot, live migration or memory preserving updates for host)
• 虚拟机正在根据预测很快会出现故障的降级主机硬件上运行Virtual machine is running on degraded host hardware that is predicted to fail soon
• 用户启动的维护（例如，用户重启或重新部署 VM）User-initiated maintenance (for example, a user restarts or redeploys a VM)

基础知识The Basics

元数据服务公开在 VM 中使用可访问的 REST 终结点运行 VM 的相关信息。Metadata Service exposes information about running VMs by using a REST endpoint that's accessible from within the VM. 该信息通过不可路由的 IP 提供，因此不会在 VM 外部公开。The information is available via a nonroutable IP so that it's not exposed outside the VM.

作用域Scope

计划的事件传送到：Scheduled events are delivered to:

• 独立虚拟机。Standalone Virtual Machines.
• 云服务中的所有 VM。All the VMs in a cloud service.
• 可用性集中的所有 VM。All the VMs in an availability set.
• 规模集位置组中的所有 VM。All the VMs in a scale set placement group.

因此，检查事件中的 Resources 字段可确定哪些 VM 受到了影响。As a result, check the Resources field in the event to identify which VMs are affected.

终结点发现Endpoint Discovery

对于启用了 VNET 的 VM，元数据服务可通过不可路由的静态 IP (169.254.169.254) 使用。For VNET enabled VMs, Metadata Service is available from a static nonroutable IP, 169.254.169.254. 最新版本的计划事件的完整终结点是：The full endpoint for the latest version of Scheduled Events is:

http://169.254.169.254/metadata/scheduledevents?api-version=2019-08-01

如果不是在虚拟网络中创建 VM（云服务和经典 VM 的默认情况），则需使用额外的逻辑以发现要使用的 IP 地址。If the VM is not created within a Virtual Network, the default cases for cloud services and classic VMs, additional logic is required to discover the IP address to use. 若要了解如何发现主机终结点，请参阅此示例。To learn how to discover the host endpoint, see this sample.

版本和区域可用性Version and Region Availability

计划事件服务受版本控制。The Scheduled Events service is versioned. 版本是必需的，当前版本为 2019-01-01。Versions are mandatory; the current version is 2019-01-01.

启用和禁用计划事件Enabling and Disabling Scheduled Events

首次为事件发出请求时，为服务启用了计划事件。Scheduled Events is enabled for your service the first time you make a request for events. 首次调用时应该会延迟响应最多两分钟。You should expect a delayed response in your first call of up to two minutes.

如果 24 小时未发出请求，将为服务禁用计划事件。Scheduled Events is disabled for your service if it does not make a request for 24 hours.

用户启动的维护User-initiated Maintenance

用户通过 Azure 门户、API、CLI 或 PowerShell 启动的 VM 维护会生成计划事件。User-initiated VM maintenance via the Azure portal, API, CLI, or PowerShell results in a scheduled event. 然后，可以在应用程序中测试维护准备逻辑，并可以通过应用程序准备用户启动的维护。You then can test the maintenance preparation logic in your application, and your application can prepare for user-initiated maintenance.

如果重启 VM，将计划 Reboot 类型的事件。If you restart a VM, an event with the type Reboot is scheduled. 如果重新部署 VM，将计划 Redeploy 类型的事件。If you redeploy a VM, an event with the type Redeploy is scheduled.

使用 APIUse the API

头文件Headers

查询元数据服务时，必须提供标头 Metadata:true 以确保不会在无意中重定向该请求。When you query Metadata Service, you must provide the header Metadata:true to ensure the request wasn't unintentionally redirected. Metadata:true 标头对于所有预定事件请求是必需的。The Metadata:true header is required for all scheduled events requests. 不在请求中包含标头会导致元数据服务发出的“错误的请求”响应。Failure to include the header in the request results in a "Bad Request" response from Metadata Service.

查询事件Query for events

只需进行以下调用即可查询计划事件：You can query for scheduled events by making the following call:

BashBash

curl -H Metadata:true http://169.254.169.254/metadata/scheduledevents?api-version=2019-08-01

响应包含计划事件的数组。A response contains an array of scheduled events. 数组为空意味着目前没有计划事件。An empty array means that currently no events are scheduled. 如果有计划事件，响应会包含事件的数组。In the case where there are scheduled events, the response contains an array of events.

{
    "DocumentIncarnation": {IncarnationID},
    "Events": [
        {
            "EventId": {eventID},
            "EventType": "Reboot" | "Redeploy" | "Freeze" | "Terminate",
            "ResourceType": "VirtualMachine",
            "Resources": [{resourceName}],
            "EventStatus": "Scheduled" | "Started",
            "NotBefore": {timeInUTC},       
            "Description": {eventDescription},
            "EventSource" : "Platform" | "User",
        }
    ]
}

事件属性Event Properties

事件计划Event Scheduling

将根据事件类型为每个事件计划将来的最小量时间。Each event is scheduled a minimum amount of time in the future based on the event type. 此时间反映在某个事件的 NotBefore 属性上。This time is reflected in an event's NotBefore property.

轮询频率Polling frequency

可根据需要频繁或偶尔轮询终结点以进行更新。You can poll the endpoint for updates as frequently or infrequently as you like. 但是，两次请求之间的时间越长，你拥有的对即将发生的事件做出响应的时间就越少。However, the longer the time between requests, the more time you potentially lose to react to an upcoming event. 大多数事件都会提前 5 到 15 分钟通知，尽管在某些情况下，可能只会提前 30 秒通知。Most events have 5 to 15 minutes of advance notice, although in some cases advance notice might be as little as 30 seconds. 为确保有尽可能多的时间采取缓解措施，我们建议你每秒轮询一次服务。To ensure that you have as much time as possible to take mitigating actions, we recommend that you poll the service once per second.

启动事件Start an event

了解即将发生的事件并完成正常关闭逻辑后，可以通过使用 EventId 对元数据服务进行 POST 调用来批准未完成的事件。After you learn of an upcoming event and finish your logic for graceful shutdown, you can approve the outstanding event by making a POST call to Metadata Service with EventId. 此调用指示 Azure 可以缩短最小通知时间（如可能）。This call indicates to Azure that it can shorten the minimum notification time (when possible).

下面是 POST 请求正文中所需的 JSON 示例。The following JSON sample is expected in the POST request body. 请求应包含 StartRequests 列表。The request should contain a list of StartRequests. 每个 StartRequest 包含想要加速的事件的 EventId：Each StartRequest contains EventId for the event you want to expedite:

{
    "StartRequests" : [
        {
            "EventId": {EventId}
        }
    ]
}

Bash 示例Bash sample

curl -H Metadata:true -X POST -d '{"StartRequests": [{"EventId": "f020ba2e-3bc0-4c40-a10b-86575a9eabd5"}]}' http://169.254.169.254/metadata/scheduledevents?api-version=2019-01-01

Python 示例Python sample

下例将查询计划事件的元数据服务器并审核所有未完成的事件。The following sample queries Metadata Service for scheduled events and approves each outstanding event:

#!/usr/bin/python

import json
import socket
import urllib2

metadata_url = "http://169.254.169.254/metadata/scheduledevents?api-version=2019-08-01"
this_host = socket.gethostname()


def get_scheduled_events():
    req = urllib2.Request(metadata_url)
    req.add_header('Metadata', 'true')
    resp = urllib2.urlopen(req)
    data = json.loads(resp.read())
    return data


def handle_scheduled_events(data):
    for evt in data['Events']:
        eventid = evt['EventId']
        status = evt['EventStatus']
        resources = evt['Resources']
        eventtype = evt['EventType']
        resourcetype = evt['ResourceType']
        notbefore = evt['NotBefore'].replace(" ", "_")
    description = evt['Description']
    eventSource = evt['EventSource']
        if this_host in resources:
            print("+ Scheduled Event. This host " + this_host +
                " is scheduled for " + eventtype + 
        " by " + eventSource + 
        " with description " + description +
        " not before " + notbefore)
            # Add logic for handling events here


def main():
    data = get_scheduled_events()
    handle_scheduled_events(data)


if __name__ == '__main__':
    main()

后续步骤Next steps

• 在 Azure 实例元数据计划事件 GitHub 存储库中查看计划事件代码示例。Review the Scheduled Events code samples in the Azure Instance Metadata Scheduled Events GitHub repository.
• 详细了解实例元数据服务中提供的 API。Read more about the APIs that are available in the Instance Metadata Service.
• Azure 中 Linux 虚拟机的计划内维护。Learn about planned maintenance for Linux virtual machines in Azure.