Ocelot是在.net core下网关的实现类库，通过Ocelot可以统一管理我们的webapi，不用再代码中调来调去的很多api地址，统一从网关调用就行了。

记录下如何简单的使用Ocelot

1.新建Gateway的网关项目，以及webapi的示例项目Service1和Service2

在Gateway项目中引用Ocelot类库通过nuget安装

2.Ocelot需要通过配置文件来实现请求的转发

建立ocelot.json配置文件

{
  "ReRoutes": [
    {
      //Upstream表示上游请求，即客户端请求到API Gateway的请求
      "UpstreamPathTemplate": "/Service1/{url}", //请求路径模板
      "UpstreamHttpMethod": [ "Get", "Post" ], //请求方法数组

      "UseServiceDiscovery": false, //启用服务发现

      //Downstream表示下游请求，即API Gateway转发的目标服务地址
      "DownstreamPathTemplate": "/api/{url}", //下游请求地址模板
      "DownstreamScheme": "http", //请求协议，目前应该是支持http和https
      //A***************指定单个转发地址
      "DownstreamHostAndPorts": [ //请求服务地址
        {
          "Host": "localhost",
          "Port": 7001
        }
      ]
    }
  ],
  "GlobalConfiguration": {
    //"ServiceDiscoveryProvider": {
    //  "Host": "127.0.0.1",
    //  "Port": 8500,
    //  "Type": "PollConsul"
    //}
  }
}

我们的目的是通过请求Gateway将请求转发到Service1的webapi上。

然后在Programe.cs是里修改CreateWebHostBuilder方法，指定读取ocelot.json配置文件，指定Gateway在7000端口

        public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
            WebHost.CreateDefaultBuilder(args)
            .ConfigureAppConfiguration((hostingContext,builder)=> {
                builder.SetBasePath(hostingContext.HostingEnvironment.ContentRootPath)
                .AddJsonFile("ocelot.json", false, true);
            })
            .UseUrls("http://localhost:7000")
                .UseStartup<Startup>();

3.在Startup.cs中注册服务

    public class Startup {
        // This method gets called by the runtime. Use this method to add services to the container.
        // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
        public void ConfigureServices(IServiceCollection services) {
            services.AddOcelot();//添加Ocelot服务
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env) {
            if (env.IsDevelopment()) {
                app.UseDeveloperExceptionPage();
            }

            app.UseOcelot().Wait();//使用Ocelot服务

            app.Run(async (context) => {
                await context.Response.WriteAsync("Hello World!");
            });
        }
    }

4.接下来对Service1的webapi示例项目中的programe.cs中指定7001端口运行

然后增加了一个webapi的控制器

namespace Service1.Controllers {
    [Route("api/[controller]/[action]")]
    [ApiController]
    public class ValuesController : ControllerBase {
        [HttpGet]
        public IActionResult GetById(string id) {
            return Content($"This is Service1 id:{id}");
        }

        public IActionResult AddUser([FromBody] dynamic userDto) {
            return Content($"Service1, User:{userDto.UserId},{userDto.Name}");
        }
    }
}

此时我们可以通过http://localhost:7001/api/Values/GetById?id=123进行访问会有内容输出

5.启动Gateway和Service1两个项目后

我们可以通过http://localhost:7000/Service1/Values/GetById?id=123进行访问了，此时我们是通过网关来进行请求转发的形式访问了。

关键是在上面的ocelot.json的配置文件中，

      "DownstreamHostAndPorts": [ //请求服务地址
        {
          "Host": "localhost",
          "Port": 7001
        }
      ]

我们将请求转发到下游host:localhost,port:7001中了。

关于Ocelot标准的配置

{
          "DownstreamPathTemplate": "/",
          "UpstreamPathTemplate": "/",
          "UpstreamHttpMethod": [
              "Get"
          ],
          "AddHeadersToRequest": {},
          "AddClaimsToRequest": {},
          "RouteClaimsRequirement": {},
          "AddQueriesToRequest": {},
          "RequestIdKey": "",
          "FileCacheOptions": {
              "TtlSeconds": 0,
              "Region": ""
          },
          "ReRouteIsCaseSensitive": false,
          "ServiceName": "",
          "DownstreamScheme": "http",
          "DownstreamHostAndPorts": [
              {
                  "Host": "localhost",
                  "Port": 51876,
              }
          ],
          "QoSOptions": {
              "ExceptionsAllowedBeforeBreaking": 0,
              "DurationOfBreak": 0,
              "TimeoutValue": 0
          },
          "LoadBalancer": "",
          "RateLimitOptions": {
              "ClientWhitelist": [],
              "EnableRateLimiting": false,
              "Period": "",
              "PeriodTimespan": 0,
              "Limit": 0
          },
          "AuthenticationOptions": {
              "AuthenticationProviderKey": "",
              "AllowedScopes": []
          },
          "HttpHandlerOptions": {
              "AllowAutoRedirect": true,
              "UseCookieContainer": true,
              "UseTracing": true
          },
          "UseServiceDiscovery": false
      }

• Downstream是下游服务配置
• UpStream是上游服务配置
• Aggregates 服务聚合配置
• ServiceName, LoadBalancer, UseServiceDiscovery 配置服务发现
• AuthenticationOptions 配置服务认证
• RouteClaimsRequirement 配置Claims鉴权
• RateLimitOptions为限流配置
• FileCacheOptions 缓存配置
• QosOptions 服务质量与熔断
• DownstreamHeaderTransform头信息转发