Ocelot閘道器(三)

下面是一個在 .NET Core 中使用 Ocelot 的簡單示例。這個示例展示瞭如何設定 Ocelot 作為 API Gateway，將請求轉發到不同的後端微服務。

步驟 1：建立專案

1. 建立一個新的 .NET Core Web 應用程式（API 專案）：

   dotnet new webapi -n OcelotGateway
   cd OcelotGateway

   建立兩個簡單的後端微服務作為示例：
   ServiceA：

   dotnet new webapi -n ServiceA
   cd ServiceA
   

   在 ServiceA/Controllers 目錄中，建立 ValuesController.cs：

   using Microsoft.AspNetCore.Mvc;
   
   [Route("api/[controller]")]
   [ApiController]
   public class ValuesController : ControllerBase
   {
       [HttpGet]
       public IActionResult Get()
       {
           return Ok(new[] { "Value from Service A - 1", "Value from Service A - 2" });
       }
   }

   ServiceB：

   dotnet new webapi -n ServiceB
   cd ServiceB

   在 ServiceB/Controllers 目錄中，建立 ValuesController.cs：

   using Microsoft.AspNetCore.Mvc;
   
   [Route("api/[controller]")]
   [ApiController]
   public class ValuesController : ControllerBase
   {
       [HttpGet]
       public IActionResult Get()
       {
           return Ok(new[] { "Value from Service B - 1", "Value from Service B - 2" });
       }
   }

   步驟 2：新增 Ocelot
   在 OcelotGateway 專案中，新增 Ocelot NuGet 包：

   dotnet add package Ocelot

   建立 ocelot.json 配置檔案，在 OcelotGateway 專案的根目錄中新增 ocelot.json 檔案，內容如下：

   {
     "Routes": [
       {
         "DownstreamPathTemplate": "/api/values",
         "DownstreamScheme": "http",
         "DownstreamHostAndPorts": [
           {
             "Host": "localhost",
             "Port": 5001
           }
         ],
         "UpstreamPathTemplate": "/servicea/values",
         "UpstreamHttpMethod": [ "GET" ]
       },
       {
         "DownstreamPathTemplate": "/api/values",
         "DownstreamScheme": "http",
         "DownstreamHostAndPorts": [
           {
             "Host": "localhost",
             "Port": 5002
           }
         ],
         "UpstreamPathTemplate": "/serviceb/values",
         "UpstreamHttpMethod": [ "GET" ]
       }
     ]
   }

   步驟 3：配置 Ocelot

   在 Startup.cs 檔案中，新增 Ocelot 的配置：

   using Ocelot.DependencyInjection;
   using Ocelot.Middleware;
   
   
   var builder = WebApplication.CreateBuilder(args);
   
   builder.Services.AddEndpointsApiExplorer();
   builder.Services.AddSwaggerGen();
   builder.Services.AddOcelot();
   
   var app = builder.Build();
   
   // Configure the HTTP request pipeline.
   if (app.Environment.IsDevelopment())
   {
       app.UseSwagger();
       app.UseSwaggerUI();
   }
   
   app.UseHttpsRedirection();
   
   
   var summaries = new[]
   {
       "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
   };
   
   app.MapGet("/weatherforecast", () =>
   {
       var forecast = Enumerable.Range(1, 5).Select(index =>
           new WeatherForecast
           (
               DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
               Random.Shared.Next(-20, 55),
               summaries[Random.Shared.Next(summaries.Length)]
           ))
           .ToArray();
       return forecast;
   })
   .WithName("GetWeatherForecast")
   .WithOpenApi();
   
   // 啟動 Ocelot
   await app.UseOcelot();
   
   app.Run();
   
   record WeatherForecast(DateOnly Date, int TemperatureC, string? Summary)
   {
       public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);
   }

   步驟 4：執行服務

   1. 在終端中，開啟三個終端視窗，分別啟動 Ocelot Gateway 和兩個微服務：

      • 啟動 ServiceA：

        cd ServiceA dotnet run

      • 啟動 ServiceB：

        cd ServiceB dotnet run

      • 啟動 OcelotGateway：

        cd OcelotGateway dotnet run

   步驟 5：測試 API Gateway

   1. 使用 Postman 或瀏覽器測試 API Gateway：

      • 訪問 Service A：

        GET http://localhost:5000/servicea/values

        應該返回：

        ["Value from Service A - 1", "Value from Service A - 2"]

      • 訪問 Service B：

        GET http://localhost:5000/serviceb/values

        應該返回：

        ["Value from Service B - 1", "Value from Service B - 2"]

   
   
   解釋json

   {
     "Routes": [
       {
         "DownstreamPathTemplate": "/api/values",
         "DownstreamScheme": "http",
         "DownstreamHostAndPorts": [
           {
             "Host": "localhost",
             "Port": 5001
           }
         ],
         "UpstreamPathTemplate": "/servicea/values",
         "UpstreamHttpMethod": [ "GET" ]
       },
       {
         "DownstreamPathTemplate": "/api/values",
         "DownstreamScheme": "http",
         "DownstreamHostAndPorts": [
           {
             "Host": "localhost",
             "Port": 5002
           }
         ],
         "UpstreamPathTemplate": "/serviceb/values",
         "UpstreamHttpMethod": [ "GET" ]
       }
     ]
   }

   解析這個示例

   1. 第一條路由：

      • 當客戶端傳送請求到 /servicea/values（UpstreamPathTemplate）時，Ocelot 會將請求轉發到 http://localhost:5001/api/values（DownstreamPathTemplate）。

   2. 第二條路由：

      • 當客戶端傳送請求到 /serviceb/values 時，Ocelot 會將請求轉發到 http://localhost:5002/api/values。