C# HttpClient 如何使用 Consul 发现服务

　　试用了Overt.Core.Grpc, 把 GRPC 的使用改造得像 WCF, 性能测试也非常不错, 非常推荐各位使用.
　　但已有项目大多是 http 请求, 改造成 GRPC 的话, 工作量比较大, 于是又找到了 Steeltoe.Discovery, 在 Startup 给 HttpClient 添加 DelegatingHandler, 动态改变请求url中的 host 和 port, 将http请求指向consul 发现的服务实例, 这样就实现了服务的动态发现.
　　经过性能测试, Steeltoe.Discovery 只有 Overt.Core.Grpc 的20%, 非常难以接受, 于是自己实现了一套基于 consul 的服务发现工具. 嗯, 名字好难取啊, 暂定为 ConsulDiscovery.HttpClient 吧
　　功能很简单:

1. webapi 从json中读取配置信息 ConsulDiscoveryOptions;
2. 如果自己是一个服务, 则将自己注册到consul中并设置健康检查Url;
3. ConsulDiscovery.HttpClient 内有一个consul client 定时刷新所有服务的url访问地址.

　　比较核心的两个类

using Consul;
using Microsoft.Extensions.Options;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;

namespace ConsulDiscovery.HttpClient
{
  public class DiscoveryClient : IDisposable
  {
    private readonly ConsulDiscoveryOptions consulDiscoveryOptions;
    private readonly Timer timer;
    private readonly ConsulClient consulClient;
    private readonly string serviceIdInConsul;

    public Dictionary<string, List<string>> AllServices { get; private set; } = new Dictionary<string, List<string>>(StringComparer.OrdinalIgnoreCase);

    public DiscoveryClient(IOptions<ConsulDiscoveryOptions> options)
    {
      consulDiscoveryOptions = options.Value;
      consulClient = new ConsulClient(x => x.Address = new Uri($"http://{consulDiscoveryOptions.ConsulServerSetting.IP}:{consulDiscoveryOptions.ConsulServerSetting.Port}"));
      timer = new Timer(Refresh);

      if (consulDiscoveryOptions.ServiceRegisterSetting != null)
      {
        serviceIdInConsul = Guid.NewGuid().ToString();
      }
    }

    public void Start()
    {
      var checkErrorMsg = CheckParams();
      if (checkErrorMsg != null)
      {
        throw new ArgumentException(checkErrorMsg);
      }
      RegisterToConsul();
      timer.Change(0, consulDiscoveryOptions.ConsulServerSetting.RefreshIntervalInMilliseconds);
    }

    public void Stop()
    {
      Dispose();
    }

    private string CheckParams()
    {
      if (string.IsNullOrWhiteSpace(consulDiscoveryOptions.ConsulServerSetting.IP))
      {
        return "Consul服务器地址 ConsulDiscoveryOptions.ConsulServerSetting.IP 不能为空";
      }

      if (consulDiscoveryOptions.ServiceRegisterSetting != null)
      {
        var registerSetting = consulDiscoveryOptions.ServiceRegisterSetting;
        if (string.IsNullOrWhiteSpace(registerSetting.ServiceName))
        {
          return "服务名称 ConsulDiscoveryOptions.ServiceRegisterSetting.ServiceName 不能为空";
        }
        if (string.IsNullOrWhiteSpace(registerSetting.ServiceIP))
        {
          return "服务地址 ConsulDiscoveryOptions.ServiceRegisterSetting.ServiceIP 不能为空";
        }
      }
      return null;
    }

    private void RegisterToConsul()
    {
      if (string.IsNullOrEmpty(serviceIdInConsul))
      {
        return;
      }

      var registerSetting = consulDiscoveryOptions.ServiceRegisterSetting;
      var httpCheck = new AgentServiceCheck()
      {
        HTTP = $"{registerSetting.ServiceScheme}{Uri.SchemeDelimiter}{registerSetting.ServiceIP}:{registerSetting.ServicePort}/{registerSetting.HealthCheckRelativeUrl.TrimStart('/')}",
        Interval = TimeSpan.FromMilliseconds(registerSetting.HealthCheckIntervalInMilliseconds),
        Timeout = TimeSpan.FromMilliseconds(registerSetting.HealthCheckTimeOutInMilliseconds),
        DeregisterCriticalServiceAfter = TimeSpan.FromSeconds(10),
      };
      var registration = new AgentServiceRegistration()
      {
        ID = serviceIdInConsul,
        Name = registerSetting.ServiceName,
        Address = registerSetting.ServiceIP,
        Port = registerSetting.ServicePort,
        Check = httpCheck,
        Meta = new Dictionary<string, string>() { ["scheme"] = registerSetting.ServiceScheme },
      };
      consulClient.Agent.ServiceRegister(registration).Wait();
    }

    private void DeregisterFromConsul()
    {
      if (string.IsNullOrEmpty(serviceIdInConsul))
      {
        return;
      }
      try
      {
        consulClient.Agent.ServiceDeregister(serviceIdInConsul).Wait();
      }
      catch
      { }
    }

    private void Refresh(object state)
    {
      Dictionary<string, AgentService>.ValueCollection serversInConsul;
      try
      {
        serversInConsul = consulClient.Agent.Services().Result.Response.Values;
      }
      catch // (Exception ex)
      {
        // 如果连接consul出错, 则不更新服务列表. 继续使用以前获取到的服务列表
        // 但是如果很长时间都不能连接consul, 服务列表里的一些实例已经不可用了, 还一直提供这样旧的列表也不合理, 所以要不要在这里实现 健康检查? 这样的话, 就得把检查地址变成不能设置的
        return;
      }

      // 1. 更新服务列表
      // 2. 如果这个程序提供了服务, 还要检测 服务Id 是否在服务列表里
      var tempServices = new Dictionary<string, HashSet<string>>();
      bool needReregisterToConsul = true;
      foreach (var service in serversInConsul)
      {
        var serviceName = service.Service;
        if (!service.Meta.TryGetValue("scheme", out var serviceScheme))
        {
          serviceScheme = Uri.UriSchemeHttp;
        }
        var serviceHost = $"{serviceScheme}{Uri.SchemeDelimiter}{service.Address}:{service.Port}";
        if (!tempServices.TryGetValue(serviceName, out var serviceHosts))
        {
          serviceHosts = new HashSet<string>();
          tempServices[serviceName] = serviceHosts;
        }
        serviceHosts.Add(serviceHost);

        if (needReregisterToConsul && !string.IsNullOrEmpty(serviceIdInConsul) && serviceIdInConsul == service.ID)
        {
          needReregisterToConsul = false;
        }
      }

      if (needReregisterToConsul)
      {
        RegisterToConsul();
      }

      var tempAllServices = new Dictionary<string, List<string>>(StringComparer.OrdinalIgnoreCase);
      foreach (var item in tempServices)
      {
        tempAllServices[item.Key] = item.Value.ToList();
      }
      AllServices = tempAllServices;
    }

    public void Dispose()
    {
      DeregisterFromConsul();
      consulClient.Dispose();
      timer.Dispose();
    }
  }
}

using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

namespace ConsulDiscovery.HttpClient
{
  public class DiscoveryHttpMessageHandler : DelegatingHandler
  {
    private static readonly Random random = new Random((int)DateTime.Now.Ticks);

    private readonly DiscoveryClient discoveryClient;

    public DiscoveryHttpMessageHandler(DiscoveryClient discoveryClient)
    {
      this.discoveryClient = discoveryClient;
    }

    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
      if (discoveryClient.AllServices.TryGetValue(request.RequestUri.Host, out var serviceHosts))
      {
        if (serviceHosts.Count > 0)
        {
          var index = random.Next(serviceHosts.Count);
          request.RequestUri = new Uri(new Uri(serviceHosts[index]), request.RequestUri.PathAndQuery);
        }
      }
      return await base.SendAsync(request, cancellationToken).ConfigureAwait(false);
    }
  }
}

　　使用方法

　　为了简单, 我为新建的WebApi 增加了一个 HelloController, 提供 SayHelloService 服务, 并把自己注册到Consul.

　　当我们访问这个WebApi的 /WeatherForecast 时, 其Get()方法会访问 http://SayHelloService/Hello/NetCore, 这就相当于一次远程调用, 只是调用的就是这个WebApi的/Hello/NetCore

　　1. appsettings.json 增加

"ConsulDiscoveryOptions": {
  "ConsulServerSetting": {
   "IP": "127.0.0.1", // 必填
   "Port": 8500, // 必填
   "RefreshIntervalInMilliseconds": 1000
  },
  "ServiceRegisterSetting": {
   "ServiceName": "SayHelloService", // 必填
   "ServiceIP": "127.0.0.1", // 必填
   "ServicePort": 5000, // 必填
   "ServiceScheme": "http", // 只能是http 或者 https, 默认http,
   "HealthCheckRelativeUrl": "/HealthCheck",
   "HealthCheckIntervalInMilliseconds": 500,
   "HealthCheckTimeOutInMilliseconds": 2000
  }
 }

　　2.修改Startup.cs

using ConsulDiscovery.HttpClient;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System;

namespace WebApplication1
{
  public class Startup
  {
    public Startup(IConfiguration configuration)
    {
      Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
      services.AddControllers();

      // 注册 ConsulDiscovery 相关配置
      services.AddConsulDiscovery(Configuration);
      // 配置 SayHelloService 的HttpClient
      services.AddHttpClient("SayHelloService", c =>
        {
          c.BaseAddress = new Uri("http://SayHelloService");
        })
        .AddHttpMessageHandler<DiscoveryHttpMessageHandler>();
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IHostApplicationLifetime lifetime)
    {
      if (env.IsDevelopment())
      {
        app.UseDeveloperExceptionPage();
      }

      app.UseRouting();

      app.UseAuthorization();

      app.UseEndpoints(endpoints =>
      {
        endpoints.MapControllers();
      });

      // 启动 ConsulDiscovery
      app.StartConsulDiscovery(lifetime);
    }
  }
}

　　3. 添加 HelloController

using Microsoft.AspNetCore.Mvc;

namespace WebApplication1.Controllers
{
  [ApiController]
  [Route("[controller]")]
  public class HelloController : ControllerBase
  {
    [HttpGet]
    [Route("{name}")]
    public string Get(string name)
    {
      return $"Hello {name}";
    }
  }
}

　　4. 修改WeatherForecast

using Microsoft.AspNetCore.Mvc;
using System.Net.Http;
using System.Threading.Tasks;

namespace WebApplication1.Controllers
{
  [ApiController]
  [Route("[controller]")]
  public class WeatherForecastController : ControllerBase
  {
    private readonly IHttpClientFactory httpClientFactory;

    public WeatherForecastController(IHttpClientFactory httpClientFactory)
    {
      this.httpClientFactory = httpClientFactory;
    }

    [HttpGet]
    public async Task<string> Get()
    {
      var httpClient = httpClientFactory.CreateClient("SayHelloService");
      var result = await httpClient.GetStringAsync("Hello/NetCore");
      return $"WeatherForecast return:      {result}";
    }
  }
}

　　5. 启动consul

consul agent -dev

　　6. 启动 WebApplication1 并访问 http://localhost:5000/weatherforecast

　　以上示例可以到 https://github.com/zhouandke/ConsulDiscovery.HttpClient 下载, 请记住一定要 启动consul:    consul agent -dev

　　End

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