Azure部署Blazor Server应用因大量_blazor请求致不稳定问题排查

1. 现象：

   • Blazor Server应用部署到Azure App Service后，浏览器Network标签出现大量指向https://mywebsites0123.azurewebsites.net/_blazor?id=3OO-T6L4Bu9bMRF8QAo_5Q&_=166722的请求，引发应用运行不稳定。
   • 本地Debug/Release模式运行时无此问题，应用流畅。
   • 已查阅Stack Overflow问题《C# Blazor server - why so many _blazor requests and such memory consumption?》，未找到有效解决方案。

2. 应用Startup配置：

   ConfigureServices(IServiceCollection services) #

   services.AddRazorPages();
   services.AddServerSideBlazor().AddMicrosoftIdentityConsentHandler();
   
   services.AddSignalR(e =>
   {
                   e.MaximumReceiveMessageSize = 2000 * 1024;
   });
   
   // Radzen init
   services.AddScoped<DialogService>();
   services.AddScoped<TooltipService>();
   services.AddScoped<NotificationService>();
   
   services.AddMemoryCache();
   
   var apiScope = Configuration["Authentication:ApiScope"];
   services.AddMicrosoftIdentityWebAppAuthentication(Configuration, "Authentication:AzureAd")
   .EnableTokenAcquisitionToCallDownstreamApi(new string[] { apiScope })
   .AddInMemoryTokenCaches();
   
   services.AddControllersWithViews().AddMicrosoftIdentityUI();
   services.AddAuthorization();
   

   Configure(IApplicationBuilder app, IWebHostEnvironment env) #

   if (env.IsDevelopment())
   {
      app.UseDeveloperExceptionPage();
   }
   else
   {
       app.UseExceptionHandler("/Error");
       app.UseHsts();
   }
   
   app.UseHttpsRedirection();
   app.UseStaticFiles();
   
   app.UseRouting();
   
   app.UseAuthentication();
   app.UseAuthorization();
   
   app.UseEndpoints(endpoints =>
   {
       endpoints.MapControllers();
       endpoints.MapBlazorHub();
       endpoints.MapFallbackToPage("/_Host");
   });
   

• 启用Azure App Service的WebSockets功能（默认处于关闭状态）。Blazor Server依赖SignalR实现双向通信，SignalR在Azure App Service中优先使用WebSockets传输，若未开启WebSockets，会自动降级为长轮询模式，这正是引发大量_blazor重复请求的原因。开启WebSockets后，SignalR会维持稳定的长连接，避免频繁请求。

内容的提问来源于stack exchange，提问作者Snake Eyes