reverse-proxy: LoadBalancingPolicy = First broken in preview 11

Describe the bug

Took us few hours to work this out. We deployed yarp preview 11 to prod for a small service. Worked as expected for 2 hours then service got restarted and yarp started using second destination. Previously this happened if first destination was unhealthy but with preview 11 it is random. This is not a problem with preview 10.

To Reproduce

Create new project and use the configurations below. Then run the https://localhost:5001/todo/v1. You’d have to run this few times by stopping the app and rebuilding it. Sometimes the configurations don’t get cleared until you rebuild the solution in VS (this is a another problem).

Here is my result I ran the project and yarp picked up second destination. If rebuild and re run few times destinations will randomly change.

{
  "Logging": {
    "LogLevel": {
      "Default": "Debug",
      "Microsoft": "Debug",
      "Microsoft.Hosting.Lifetime": "Debug"
    }
  },
  "AllowedHosts": "*",
  "ReverseProxy": {
    "Routes": {
      "Route8": {
        "ClusterId": "cluster1",
        "Match": {
          "Methods": [ "GET" ],
          "Path": "/todo/v1"
        },
        "Transforms": [
          {
            "PathSet": ""
          },
          {
            "ResponseHeader": "Access-Control-Expose-Headers",
            "Append": "IsSuccessful",
            "When": "Always"
          },
          {
            "ResponseHeader": "Access-Control-Max-Age",
            "Append": "86400",
            "When": "Always"
          }
        ]
      }
    },
    "Clusters": {
      "cluster1": {
        "LoadBalancingPolicy": "First",
        "HealthCheck": {
          "Passive": {
            "Enabled": "true",
            "Policy": "TransportFailureRate",
            "ReactivationPeriod": "00:01:01"
          }
        },
        "HttpRequest": {
          "Timeout": "00:01:00",
          "Version": "1.1"
        },
        "Destinations": {
          "cluster1_destination1": {
            "Address": "https://jsonplaceholder.typicode.com/todos/1"
          },
          "cluster2_destination2": {
            "Address": "https://jsonplaceholder.typicode.com/todos/2"
          }
        }
      }
    }
  }
}

Startup

public class Startup
    {
        public IConfiguration Configuration { get; }

        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddReverseProxy().LoadFromConfig(Configuration.GetSection("ReverseProxy"));
           
            services.AddCors(options => options.AddPolicy("EnableCors", builder =>
            {
                builder.AllowAnyOrigin().SetPreflightMaxAge(TimeSpan.FromSeconds(86400));
                builder.AllowAnyMethod().SetPreflightMaxAge(TimeSpan.FromSeconds(86400));
                builder.AllowAnyHeader().SetPreflightMaxAge(TimeSpan.FromSeconds(86400));
            }));
        }

        public void Configure(IApplicationBuilder app)
        {
            //app.UseMiddleware<ExceptionMiddleware>();
            app.UseCors("EnableCors");
            app.UseRouting();
            app.UseEndpoints(endpoints =>
            {
                endpoints.MapReverseProxy();
            });

        }
    }

Further technical details

• Package Yarp.ReverseProxy - 1.0.0-preview.11.*
• The platform - Windows