面试题：C# 的 Ocelot 如何实现动态路由配置

配置文件修改

添加自定义配置：在 ocelot.json 配置文件中，对于需要动态路由的路由规则，可以添加自定义配置项。例如：

{
    "Routes": [
        {
            "DownstreamPathTemplate": "/{everything}",
            "DownstreamScheme": "http",
            "UpstreamPathTemplate": "/{everything}",
            "UpstreamHttpMethod": [ "Get", "Post", "Put", "Delete" ],
            "CustomConfig": {
                "DynamicRoutingField": "YourHeaderFieldName"
            }
        }
    ],
    "GlobalConfiguration": {
        "BaseUrl": "http://localhost:5000"
    }
}

这里在 CustomConfig 中定义了一个 DynamicRoutingField，表示根据请求头中的 YourHeaderFieldName 字段来动态路由。

代码实现思路

创建自定义路由选择器：继承 IOcelotRequestScopedMiddleware 接口来创建一个自定义中间件。

using Microsoft.AspNetCore.Http;
using Ocelot.Infrastructure.RequestData;
using Ocelot.Middleware;
using Ocelot.Responses;
using System.Threading.Tasks;

public class DynamicRoutingMiddleware : IOcelotRequestScopedMiddleware
{
    private readonly RequestDelegate _next;
    private readonly IOcelotRequestDataRepository _requestDataRepository;

    public DynamicRoutingMiddleware(RequestDelegate next, IOcelotRequestDataRepository requestDataRepository)
    {
        _next = next;
        _requestDataRepository = requestDataRepository;
    }

    public async Task Invoke(HttpContext httpContext)
    {
        var route = _requestDataRepository.Get<DownstreamRoute>();
        if (route.Data != null)
        {
            var customConfig = route.Data.Options.CustomOptions;
            if (customConfig != null && customConfig.ContainsKey("DynamicRoutingField"))
            {
                var headerField = customConfig["DynamicRoutingField"] as string;
                if (httpContext.Request.Headers.TryGetValue(headerField, out var headerValue))
                {
                    // 根据 headerValue 修改下游服务地址
                    var downstreamHostAndPorts = new List<DownstreamHostAndPort>();
                    // 这里根据业务逻辑构建新的下游地址
                    var newDownstreamUrl = GetDownstreamUrlBasedOnHeader(headerValue);
                    downstreamHostAndPorts.Add(new DownstreamHostAndPort(newDownstreamUrl.Host, newDownstreamUrl.Port));
                    route.Data.DownstreamHostAndPorts = downstreamHostAndPorts;
                }
            }
        }

        await _next.Invoke(httpContext);
    }

    private Uri GetDownstreamUrlBasedOnHeader(string headerValue)
    {
        // 根据请求头值返回不同的下游服务地址
        // 这里是示例逻辑，实际应根据业务需求实现
        if (headerValue == "value1")
        {
            return new Uri("http://service1:5001");
        }
        else if (headerValue == "value2")
        {
            return new Uri("http://service2:5002");
        }
        return new Uri("http://defaultService:5003");
    }

    public string Name => "DynamicRoutingMiddleware";
}

注册中间件：在 Startup.cs 文件中注册该中间件。

using Ocelot.DependencyInjection;
using Ocelot.Middleware;

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

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        app.UseWhen(context => context.Request.Path.StartsWithSegments("/api"), appBuilder =>
        {
            appBuilder.UseMiddleware<DynamicRoutingMiddleware>();
        });

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

这样就可以在 Ocelot 中根据请求头中的特定字段动态配置路由规则。

面试题：C# 的 Ocelot 如何实现动态路由配置

知识考点

面试题答案

配置文件修改

代码实现思路