问题描述

App Service开启多实例后，如何在代码中获取当前请求所真实达到的实例呢？

问题答案

App Service为通过环境变量的方式来显示输出实例ID等信息，如：

Website Environment Variables

• WEBSITE_SITE_NAME - The name of the site.
• WEBSITE_SKU - The sku of the site (Possible values: Free, Shared, Basic, Standard).
• WEBSITE_COMPUTE_MODE - Specifies whether website is on a dedicated or shared VM/s (Possible values: Shared, Dedicated).
• WEBSITE_HOSTNAME - The Azure Website's primary host name for the site (For example: site.azurewebsites.net). Note that custom hostnames are not accounted for here.
• WEBSITE_INSTANCE_ID - The id representing the VM that the site is running on (If site runs on multiple instances, each instance will have a different id).
• WEBSITE_NODE_DEFAULT_VERSION - The default node version this website is using.
• WEBSOCKET_CONCURRENT_REQUEST_LIMIT - The limit for websocket's concurrent requests.
• WEBSITE_COUNTERS_ALL - (Windows only) all perf counters (ASPNET, APP and CLR) in JSON format. You can access specific one such as ASPNET by WEBSITE_COUNTERS_ASPNET.

可以通过App Service的高级管理工具(Kudu站点）来查看这些信息：

 

所以如果要在代码中获取Instance ID信息，可以直接通过  var instanceID = Configuration["WEBSITE_INSTANCE_ID"] 获取。全部实例代码为：

Index.cshtml.cs :

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;

namespace MyFirstAzureWebApp.Pages;

public class IndexModel : PageModel
{
    private readonly IConfiguration Configuration;
 
    private readonly ILogger<IndexModel> _logger;

    public IndexModel(ILogger<IndexModel> logger, IConfiguration configuration)
    {
        _logger = logger;
        Configuration = configuration;
    }

    public void OnGet()
    {
        var instanceID = Configuration["WEBSITE_INSTANCE_ID"];

        ViewData["InstanceID"] = instanceID;

        //return Content($"Instance ID value: {instanceID} \n");
    }
}

如要快速创建一个ASP.NET应用来验证Instance ID，可以参考文档：https://docs.azure.cn/zh-cn/app-service/quickstart-dotnetcore?tabs=net60#create-an-aspnet-web-app

Index.cshtml 文件内容为：

@page
@model IndexModel
@{
    ViewData["Title"] = "Home page";
}

<div class="text-center">
    <h1 class="display-4">Welcome</h1>
     <div>
        The current Instance ID is:@ViewData["InstanceID"];
    </div>
    <hr />
    <p>Learn about <a href="https://docs.microsoft.com/aspnet/core">building Web apps with ASP.NET Core</a>.</p>
   
</div>

 

发布到App Service后，就可以检验效果：

此外，如果App Service开启了ARR Affinity(请求粘连性)功能后，在客户端的Cookie值ARRAffinity和ARRAffinitySameSite中，也是可以找到Instance ID信息。如:

 

 

参考资料

Azure runtime environment：https://github.com/projectkudu/kudu/wiki/Azure-runtime-environment#website-environment-variables

快速入门：部署 ASP.NET Web 应用：https://docs.azure.cn/zh-cn/app-service/quickstart-dotnetcore?tabs=net60#create-an-aspnet-web-app