上一篇定义了两种使用Jaeger的方式：中间件和action过滤器，下面这个例子定义了两个服务 WebAPI01，请求WebAPI02，采用的是中间件的请求方式。

引入JaegerSharp包（或发布到自己的Nuget库里引用）

WebAPI01的Startup

using JaegerSharp;using Microsoft.AspNetCore.Builder;using Microsoft.AspNetCore.Hosting;using Microsoft.Extensions.Configuration;using Microsoft.Extensions.DependencyInjection;using Microsoft.Extensions.Hosting;using Microsoft.OpenApi.Models;using System;namespace WebAPI01{    public class Startup    {        public Startup(IConfiguration configuration)        {            Configuration = configuration;        }        public IConfiguration Configuration { get; }        public void ConfigureServices(IServiceCollection services)        {            //命名客户端            services.AddHttpClient("WebAPI02", client =>            {                client.BaseAddress = new Uri(Configuration.GetSection("DownStreamUrl").Value);            });            services.AddControllers();            services.AddSwaggerGen(c =>            {                c.SwaggerDoc("v1", new OpenApiInfo { Title = "WebAPI01", Version = "v1" });            });            //添加OpenTracing            services.AddOpenTracing();            //注入Jaeger            if (Convert.ToBoolean(Configuration.GetSection("OpenTracing:Enable")?.Value))            {                var agentHost = Configuration.GetSection("OpenTracing:Agent").GetValue
    
     ("Host");                var agentPort = Configuration.GetSection("OpenTracing:Agent").GetValue
     
      ("Port");                var agentMaxPacketSize = Configuration.GetSection("OpenTracing:Agent").GetValue
      
       ("MaxPacketSize");                services.AddJaegerSharp(agentHost, agentPort, agentMaxPacketSize);            }        }        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)        {            if (env.IsDevelopment())            {                app.UseDeveloperExceptionPage();                app.UseSwagger();                app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", "WebAPI01 v1"));            }            app.UseHttpsRedirection();            if (Convert.ToBoolean(Configuration.GetSection("OpenTracing:Enable")?.Value))            {                app.UseJaegerSharp();            }            app.UseRouting();            app.UseAuthorization();            app.UseEndpoints(endpoints =>            {                endpoints.MapControllers();            });        }    }}
      
     
    

WebAPI01的appsettings.json

{  "Logging": {    "LogLevel": {      "Default": "Information",      "Microsoft": "Warning",      "Microsoft.Hosting.Lifetime": "Information"    }  },  "OpenTracing": {    "Enable": true,    "Agent": {      "Host": "localhost",      "Port": 6831,      "MaxPacketSize": 0    }  },  "DownStreamUrl": "https://localhost:6001"}

调用下游服务 WebAPI02，下游服务 WebAPI02与WebAPI01类似，需要引入JaegerSharp，添加配置文件，指向同一个Jaeger的host，如果WebAPI02有下游API调用，继续配置调用。

using Microsoft.AspNetCore.Mvc;using Microsoft.Extensions.Logging;using System.Net.Http;using System.Threading.Tasks;namespace WebAPI01.Controllers{    [ApiController]    [Route("[controller]")]    public class HomeController : ControllerBase    {        private readonly IHttpClientFactory _clientFactory;        private readonly ILogger
    
      _logger;        public HomeController(ILogger
     
       logger, IHttpClientFactory clientFactory)        {            _clientFactory = clientFactory;            _logger = logger;        }        [HttpGet]        public async Task
      
        Get()        {            _logger.LogInformation("WebAPI01中请求WebAPI02");            var result = await GetWebAPI02();            return $"WebAPI01请求WebAPI02返回值 :{ result}";        }        async Task
       
         GetWebAPI02()        {            using var client = _clientFactory.CreateClient("WebAPI02");            var request = new HttpRequestMessage(HttpMethod.Get, "/home");            using var response = await client.SendAsync(request);            if (response.IsSuccessStatusCode)            {                var result = await response.Content.ReadAsStringAsync();                return result;            }            else            {                return "error";            }        }    }}
       
      
     
    

下载Jaeger(https://www.jaegertracing.io/download/)，我用的是1.21.0的Windows版本，因为我的开发环境是Windows，运行jaeger-all-in-one.exe

，再跑自己的应用，访问完链路后，打开localhost:16686，查看结果如下：

查询WebAPI01结果

点击WebAPI01:HTTP GET 7151a0a结果如下，链路清晰