C# HttpClient 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(, 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(),
            };
            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 > )
                {
                    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