.NET Core 下的 API 網關

網關介紹

網關其實就是將我們寫好的API全部放在一個統一的地址暴露在公網，提供訪問的一個入口。在 .NET Core下可以使用Ocelot來幫助我們很方便的接入API 網關。與之類似的庫還有ProxyKit，微軟也發佈了一個反向代理的庫YARP。

關於網關的介紹不多說了，網上文章也挺多的，這些都是不錯的選擇，聽說後期Ocelot將會使用YARP來重寫。本篇主要實踐一下在.NET Core環境下使用Ocelot。

Ocelot官網：https://threemammals.com/ocelot
Ocelot文檔：https://ocelot.readthedocs.io
GitHub：https://github.com/ThreeMammals/Ocelot
Ocelot資源彙總：https://www.cnblogs.com/shanyou/p/10363360.html

接入使用

接口示例

先創建幾個項目用於測試，創建兩個默認的API項目，Api_A和Api_B，在創建一個網關項目Api_Gateway，網關項目可以選擇空的模板。

現在分別在Api_A和Api_B中寫幾個api，將默認的WeatherForecastController中返回模型WeatherForecast添加一個字段Source，用於區分是哪個API返回的數據。

using System;

namespace Api_A
{
    public class WeatherForecast
    {
        public string Source { get; set; } = "Api_A";

        public DateTime Date { get; set; }

        public int TemperatureC { get; set; }

        public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);

        public string Summary { get; set; }
    }
}

using System;

namespace Api_B
{
    public class WeatherForecast
    {
        public string Source { get; set; } = "Api_B";

        public DateTime Date { get; set; }

        public int TemperatureC { get; set; }

        public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);

        public string Summary { get; set; }
    }
}

直接使用WeatherForecastController默認方法，在路由中添加api前綴。

using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;
using System.Linq;

namespace Api_A.Controllers
{
    [ApiController]
    [Route("api/[controller]")]
    public class WeatherForecastController : ControllerBase
    {
        private static readonly string[] Summaries = new[]
        {
            "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
        };

        [HttpGet]
        public IEnumerable<WeatherForecast> Get()
        {
            var rng = new Random();
            return Enumerable.Range(1, 5).Select(index => new WeatherForecast
            {
                Date = DateTime.Now.AddDays(index),
                TemperatureC = rng.Next(-20, 55),
                Summary = Summaries[rng.Next(Summaries.Length)]
            }).ToArray();
        }
    }
}

using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;
using System.Linq;

namespace Api_B.Controllers
{
    [ApiController]
    [Route("api/[controller]")]
    public class WeatherForecastController : ControllerBase
    {
        private static readonly string[] Summaries = new[]
        {
            "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
        };

        [HttpGet]
        public IEnumerable<WeatherForecast> Get()
        {
            var rng = new Random();
            return Enumerable.Range(1, 5).Select(index => new WeatherForecast
            {
                Date = DateTime.Now.AddDays(index),
                TemperatureC = rng.Next(-20, 55),
                Summary = Summaries[rng.Next(Summaries.Length)]
            }).ToArray();
        }
    }
}

再分別在Api_A和Api_B中添加兩個控制器：ApiAController、ApiBController，然後加上幾個簡單的restful api。

using Microsoft.AspNetCore.Mvc;
using System.Collections.Generic;

namespace Api_A.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class ApiAController : ControllerBase
    {
        [HttpGet]
        public IEnumerable<string> Get()
        {
            return new string[] { "value1", "value2" };
        }

        [HttpGet("{id}")]
        public string Get(int id)
        {
            return $"Get：{id}";
        }

        [HttpPost]
        public string Post([FromForm] string value)
        {
            return $"Post:{value}";
        }

        [HttpPut("{id}")]
        public string Put(int id, [FromForm] string value)
        {
            return $"Put:{id}:{value}";
        }

        [HttpDelete("{id}")]
        public string Delete(int id)
        {
            return $"Delete:{id}";
        }
    }
}

using Microsoft.AspNetCore.Mvc;
using System.Collections.Generic;

namespace Api_B.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class ApiBController : ControllerBase
    {
        [HttpGet]
        public IEnumerable<string> Get()
        {
            return new string[] { "value1", "value2" };
        }

        [HttpGet("{id}")]
        public string Get(int id)
        {
            return $"Get：{id}";
        }

        [HttpPost]
        public string Post([FromForm] string value)
        {
            return $"Post:{value}";
        }

        [HttpPut("{id}")]
        public string Put(int id, [FromForm] string value)
        {
            return $"Put:{id}:{value}";
        }

        [HttpDelete("{id}")]
        public string Delete(int id)
        {
            return $"Delete:{id}";
        }
    }
}

方便查看接口，這裏添加一下swagger組件，這樣我們Api_A和Api_B項目分別就有了6個接口。

接着打包docker鏡像，放在docker中運行這兩個api項目。這一步可以用任何你熟悉的方式，run起來即可。

docker build -t api_a:dev -f ./Api_A/Dockerfile .
docker build -t api_b:dev -f ./Api_B/Dockerfile .

build成功後，指定兩個端口運行api項目。

docker run -d -p 5050:80 --name api_a api_a:dev
docker run -d -p 5051:80 --name api_b api_b:dev

Api_A指定了5050端口，通過 http://localhost:5050/swagger打開可以看到swagger文檔界面，Api_B指定了5051端口，通過 http://localhost:5051/swagger打開可以看到swagger文檔界面，這樣就大功告成了，接下來纔是重點將兩個api項目配置到Api_Gateway網關項目中。

配置網關

在網關項目Api_Gateway中都添加Ocelot組件包。

Install-Package Ocelot

Ocelot中最關鍵的就是配置路由信息，新建一個ocelot.json配置文件，將我們的兩個API接口匹配規則放進去。

{
  "Routes": [
    //ApiA
    {
      "DownstreamPathTemplate": "/api/WeatherForecast",
      "DownstreamScheme": "http",
      "DownstreamHostAndPorts": [
        {
          "Host": "localhost",
          "Port": 5050
        }
      ],
      "UpstreamPathTemplate": "/ApiA/WeatherForecast",
      "UpstreamHttpMethod": [ "Get" ]
    },
    {
      "DownstreamPathTemplate": "/api/ApiA",
      "DownstreamScheme": "http",
      "DownstreamHostAndPorts": [
        {
          "Host": "localhost",
          "Port": 5050
        }
      ],
      "UpstreamPathTemplate": "/ApiA",
      "UpstreamHttpMethod": [ "Get", "POST" ]
    },
    {
      "DownstreamPathTemplate": "/api/ApiA/{id}",
      "DownstreamScheme": "http",
      "DownstreamHostAndPorts": [
        {
          "Host": "localhost",
          "Port": 5050
        }
      ],
      "UpstreamPathTemplate": "/ApiA/{id}",
      "UpstreamHttpMethod": [ "Get", "Put", "Delete" ]
    },
    //ApiB
    {
      "DownstreamPathTemplate": "/api/WeatherForecast",
      "DownstreamScheme": "http",
      "DownstreamHostAndPorts": [
        {
          "Host": "localhost",
          "Port": 5051
        }
      ],
      "UpstreamPathTemplate": "/ApiB/WeatherForecast",
      "UpstreamHttpMethod": [ "Get" ]
    },
    {
      "DownstreamPathTemplate": "/api/ApiB",
      "DownstreamScheme": "http",
      "DownstreamHostAndPorts": [
        {
          "Host": "localhost",
          "Port": 5051
        }
      ],
      "UpstreamPathTemplate": "/ApiB",
      "UpstreamHttpMethod": [ "Get", "POST" ]
    },
    {
      "DownstreamPathTemplate": "/api/ApiB/{id}",
      "DownstreamScheme": "http",
      "DownstreamHostAndPorts": [
        {
          "Host": "localhost",
          "Port": 5051
        }
      ],
      "UpstreamPathTemplate": "/ApiB/{id}",
      "UpstreamHttpMethod": [ "Get", "Put", "Delete" ]
    }
  ],
  "GlobalConfiguration": {
    "BaseUrl": "https://localhost:44335"
  }
}

關於配置文件中的各項具體含義，可以參考官方文檔中的介紹。主要就是將DownstreamPathTemplate模板內容轉換爲UpstreamPathTemplate模板內容進行接口的訪問，同時可以指定HTTP請求的方式等等。GlobalConfiguration中的BaseUrl爲我們暴漏出去的網關地址。

設置好ocelot.json後，需要在代碼中使用它，在Program.cs中添加配置文件。

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;

namespace Api_Gateway
{
    public class Program
    {
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureAppConfiguration((context, config) =>
                {
                    config.AddJsonFile("ocelot.json", optional: false, reloadOnChange: true);
                })
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }
}

在Startup.cs中使用Ocelot。

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Ocelot.DependencyInjection;
using Ocelot.Middleware;

namespace Api_Gateway
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddOcelot();
        }

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

            app.UseRouting();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapGet("/", async context =>
                {
                    await context.Response.WriteAsync("Hello World!");
                });
            });

            app.UseOcelot().Wait();
        }
    }
}

完成以上操作後，我們試着去調用接口看看能否正確獲取預期數據。

curl -X GET "https://localhost:44335/ApiA"
curl -X GET "https://localhost:44335/ApiB"

curl -X POST "https://localhost:44335/ApiA" -H "Content-Type: multipart/form-data" -F "value=ApiA"
curl -X POST "https://localhost:44335/ApiB" -H "Content-Type: multipart/form-data" -F "value=ApiB"

curl -X GET "https://localhost:44335/ApiA/12345"
curl -X GET "https://localhost:44335/ApiB/12345"

curl -X PUT "https://localhost:44335/ApiA/12345" -H "Content-Type: multipart/form-data" -F "value=ApiA"
curl -X PUT "https://localhost:44335/ApiB/12345" -H "Content-Type: multipart/form-data" -F "value=ApiB"

curl -X DELETE "https://localhost:44335/ApiA/12345"
curl -X DELETE "https://localhost:44335/ApiB/12345"

curl -X GET "https://localhost:44335/ApiA/WeatherForecast"
curl -X GET "https://localhost:44335/ApiB/WeatherForecast"

可以看到，兩個項目中的接口全部可以通過網關項目暴露的地址進行中轉，是不是很方便？

本篇只是簡單的應用，對於Ocelot的功能遠不止於此，它非常強大，還可以實現請求聚合、服務發現、認證、鑑權、限流熔斷、並內置了負載均衡器，而且這些功能都是隻需要簡單的配置即可完成。就不一一描述了，如有實際開發需求和問題，可以查看官方文檔和示例。

.NET Core 下的 API 網關

網關介紹

接入使用

接口示例

配置網關

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