如何确保新的自动缩放 Azure 应用服务实例在处理流量之前是热的?

问题描述

在应用服务上启用自动缩放后，Azure 将根据设置规则根据需要添加实例.我总是从至少 2 个实例开始.我想确保在应用程序代码完全初始化之前，流量不会被定向到新的应用程序服务实例.我怎样才能做到这一点?是否可以添加超时?还是以某种方式自动完成?

解决方案

如果您使用水平缩放(也称为横向扩展和横向扩展)，Azure 将在供应新资源时保持您的应用程序继续运行而不会中断.

Azure 将自动预热新实例的应用程序并添加负载平衡以自动在它们之间分配请求.您不需要自己单独配置负载均衡.

有关 azure 自动缩放如何工作的更多详细信息，您可以参考此

日志结果:

fr00030.xml(你可以发现进程是5860老实例):

fr00031.xml(你可以发现进程是8164个新实例，耗时4015毫秒)

此外，正如 Byron Tardif 所说，如果您想启用自定义预热(预热所有页面)，您可以使用 应用程序初始化模块.

它也会在新请求访问您的第二个 Web 应用实例之前被调用.

With autoscaling turned on on an app service, Azure will add instances as needed based on set rules. I always start from a minimum of 2 instances. I'd like to make sure that traffic is not directed to the new app service instance until the application code has fully initialized. How can I do this? IS it possible to add a timeout? Or is it done automatically somehow?

解决方案

If you use horizontal scaling, also called scaling out and in, azure will keep your application continues running without interruption as new resources are provisioned.

Azure will automatically warm up the new instance's application and add a Load Balance to distribute the requests between them automatically. You don't need to configure the load balance separately by yourself.

More details about how azure auto scale work, you could refer to this article and this article.

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After the web app scale out to the 2 instance, if the new request are send to the default instance web site , azure will warm up the new instance's web app.

You could write a test as below:

Add below config codes in web.config's webserver tag to trace all the request:

<tracing>
  <traceFailedRequests>
    <clear/>
    <add path="*">
      <traceAreas>
      <add provider="WWW Server" areas="Authentication,Security,Filter,StaticFile,CGI,Compression,Cache,RequestNotifications,Module,Rewrite,iisnode" verbosity="Verbose" />
      </traceAreas>
      <failureDefinitions statusCodes="200-600" />
    </add>
  </traceFailedRequests>
</tracing>

Then if your site scale out to 2 instance, after you access the web app. Load balance will not redirect the request to the second instance since the instance's process doesn't start. Azure will auto warm up the second instance's web app.

You could find the log as below image shows:

The log result:

fr00030.xml(you could find the process is 5860 old instance):

fr00031.xml(you could find the process is 8164 new instance and takes 4015 msec)

Besides, as Byron Tardif says, if you want to enable custom warm up(warm up all the pages), you could use Application Initialization Module.

It will also be called before the new request access your second web app instance.

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