{
 "Routes": [
 {
  //下游路由服务地址
  "DownstreamPathTemplate": "/api/values",
  //下游服务地址访问协议类型http或者https
  "DownstreamScheme": "http",
  //下游服务的主机和端口
  "DownstreamHostAndPorts": [
  {
   "Host": "localhost",
   "Port": 9001
  },
  {
   "Host": "localhost",
   "Port": 9002
  }
  ],
  //上游服务地址，即下游服务真实访问地址
  "UpstreamPathTemplate": "/",
  //负载均衡类型：轮询
  "LoadBalancerOptions": {
  "Type": "RoundRobin"
  },
  //上游服务HTTP请求方式，例如Get、Post
  "UpstreamHttpMethod": [ "Get" ]
 }
 ]
}

{
 "DownstreamPathTemplate": "/api/posts/{postId}",
 "DownstreamScheme": "https",
 "UpstreamPathTemplate": "/posts/{postId}",
 "UpstreamHttpMethod": [ "Put" ],
 "ServiceName": "product",
 "LoadBalancerOptions": {
  "Type": "LeastConnection"
 }
}

public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
 WebHost.CreateDefaultBuilder(args)
   //.UseStartup<Startup>()
   .UseUrls("http://*:9000")
   .ConfigureAppConfiguration((hostingContext, config) =>
  {
   config.SetBasePath(hostingContext.HostingEnvironment.ContentRootPath)
    //添加Ocelot配置文件
.AddJsonFile("configuration.json")
    .AddEnvironmentVariables();
  })
  .ConfigureServices(s =>
  {
   //添加Ocelot服务;
   s.AddOcelot();
  })
  .Configure(a =>
  {
　　　　//使用Ocelot
   a.UseOcelot().Wait();
  });

//APIServicesA
[Route("api/[controller]")]
public class ValuesController : Controller
{
 // GET api/values
 [HttpGet]
 public string Get()
 {
  return "From APIServiceA";
 }
}
//APIServicesB
[Route("api/[controller]")]
public class ValuesController : Controller
{
 // GET api/values
 [HttpGet]
 public string Get()
 {
  return "From APIServiceB";
 }  
}

dotnet run --project APIGateway项目路径\APIGateway.csproj

dotnet run --project APIGateway项目路径\APIGateway.csproj

dotnet run --project APIServicesB项目路径\APIServicesB.csproj

public class CustomLoadBalancer : ILoadBalancer
{
 private readonly Func<Task<List<Service> _services;
 private readonly object _lock = new object();
 private int _last;

 public CustomLoadBalancer(Func<Task<List<Service> services)
 {
  _services = services;
 }
 public async Task<Response<ServiceHostAndPort Lease(HttpContext httpContext)
 {
  var services = await _services();
  lock (_lock)
  {
   if (_last >= services.Count)
   {
    _last = 0;
   }
   var next = services[_last];
   _last++;
   return new OkResponse<ServiceHostAndPort>(next.HostAndPort);
  }
 }
 public void Release(ServiceHostAndPort hostAndPort)
 {
 }
}

Func<IServiceProvider, DownstreamRoute, IServiceDiscoveryProvider, CustomLoadBalancer> loadBalancerFactoryFunc =
(serviceProvider, Route, serviceDiscoveryProvider) => new CustomLoadBalancer(serviceDiscoveryProvider.Get);
s.AddOcelot().AddCustomLoadBalancer(loadBalancerFactoryFunc);

"LoadBalancerOptions": {
 "Type": "CustomLoadBalancer"
}