http流量镜像

"流量镜像"是指将网络中的数据流量复制一份，并将这份复制流量发送到另一个目的地（如监控、分析或安全检测系统）。这项技术常用于网络安全、故障排查、业务灰度发布等场景。

主要应用场景

安全监控与威胁检测

将生产环境的流量镜像到安全分析设备（如IDS/IPS），用于实时监控和威胁检测。
性能分析与故障排查

将流量镜像到分析平台，对网络异常、延迟、丢包等问题进行实时排查和定位。
灰度发布和A/B测试

将真实用户流量镜像到新版本服务，进行灰度环境验证和兼容性测试，不影响真实用户体验。
合规与审计

对重要业务流量进行行为记录，以满足合规和审计要求。

VKProxy 目前只支持 http流量镜像, 需注意由于会再一次发送http 请求，请求body会临时暂存内存，所以无论内存还是请求延迟都会受到影响，特别body很大的请求

设置

大家可以在Metadata中设置缓存，具体设置项如下

MirrorCluster

镜像流量发送到的集群id

配置示例：

json 复制代码

{
  "ReverseProxy": {
    "Routes": {
      "a": {
        "Order": 0,
        "Match": {
            "Hosts": [ "api.com" ],
            "Paths": [ "*" ]
        },
        "ClusterId": "apidemo",
        "Metadata": {
          "MirrorCluster": "apidemoMirror"
        }
      }
    },
    "Clusters": {
      "apidemo": {
        "LoadBalancingPolicy": "Hash",
        "Metadata": {
          "HashBy": "header",
          "Key": "X-forwarded-For"
        },
        "Destinations": [
          {
            "Address": "https://xxx.lt"
          }
        ]
      },
      "apidemoMirror": {
        "LoadBalancingPolicy": "Hash",
        "Metadata": {
          "HashBy": "header",
          "Key": "X-forwarded-For"
        },
        "Destinations": [
          {
            "Address": "http://xxx.org/"
          }
        ]
      }
    }
  }
}

具体实现

首先需要缓存body 内容，这里实现一个简单的 ReadBufferingStream

csharp 复制代码

public class ReadBufferingStream : Stream, IDisposable
{
    private readonly SparseBufferWriter<byte> bufferWriter;
    protected Stream innerStream;

    public ReadBufferingStream(Stream innerStream)
    {
        this.innerStream = innerStream;
        bufferWriter = new SparseBufferWriter<byte>();
    }

    public override bool CanRead => innerStream.CanRead;

    public override bool CanSeek => innerStream.CanSeek;

    public override bool CanWrite => innerStream.CanWrite;

    public override long Length => innerStream.Length;

    public override long Position
    {
        get => innerStream.Position;
        set => innerStream.Position = value;
    }

    public override int WriteTimeout
    {
        get => innerStream.WriteTimeout;
        set => innerStream.WriteTimeout = value;
    }

    public Stream BufferingStream => bufferWriter.AsStream(true);

    public override void Flush()
    {
        innerStream.Flush();
    }

    public override Task FlushAsync(CancellationToken cancellationToken)
    {
        return innerStream.FlushAsync(cancellationToken);
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        var res = innerStream.Read(buffer, offset, count);

        // Zero-byte reads (where the passed in buffer has 0 length) can occur when using PipeReader, we don't want to accidentally complete the RequestBody logging in this case
        if (count == 0)
        {
            return res;
        }

        bufferWriter.Write(buffer.AsSpan(offset, res));

        return res;
    }

    public override async Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
    {
        var res = await innerStream.ReadAsync(buffer.AsMemory(offset, count), cancellationToken);

        if (count == 0)
        {
            return res;
        }

        bufferWriter.Write(buffer.AsSpan(offset, res));

        return res;
    }

    public override long Seek(long offset, SeekOrigin origin)
    {
        return innerStream.Seek(offset, origin);
    }

    public override void SetLength(long value)
    {
        innerStream.SetLength(value);
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        innerStream.Write(buffer, offset, count);
    }

    public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
    {
        return innerStream.WriteAsync(buffer, offset, count, cancellationToken);
    }

    public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken cancellationToken = default)
    {
        return innerStream.WriteAsync(buffer, cancellationToken);
    }

    public override void Write(ReadOnlySpan<byte> buffer)
    {
        innerStream.Write(buffer);
    }

    public override IAsyncResult BeginRead(byte[] buffer, int offset, int count, AsyncCallback? callback, object? state)
    {
        return innerStream.BeginRead(buffer, offset, count, callback, state);
    }

    public override IAsyncResult BeginWrite(byte[] buffer, int offset, int count, AsyncCallback? callback, object? state)
    {
        return innerStream.BeginWrite(buffer, offset, count, callback, state);
    }

    public override int EndRead(IAsyncResult asyncResult)
    {
        return innerStream.EndRead(asyncResult);
    }

    public override void EndWrite(IAsyncResult asyncResult)
    {
        innerStream.EndWrite(asyncResult);
    }

    public override async ValueTask<int> ReadAsync(Memory<byte> buffer, CancellationToken cancellationToken = default)
    {
        var res = await innerStream.ReadAsync(buffer, cancellationToken);
        if (buffer.IsEmpty)
        {
            return res;
        }

        bufferWriter.Write(buffer.Slice(0, res).Span);

        return res;
    }

    public override ValueTask DisposeAsync()
    {
        return innerStream.DisposeAsync();
    }

    protected override void Dispose(bool disposing)
    {
        if (disposing)
        {
            bufferWriter.Dispose();
        }
    }
}

然后利用中间件进行镜像处理

csharp 复制代码

public class MirrorFunc : IHttpFunc
{
    private readonly IServiceProvider serviceProvider;
    private readonly IHttpForwarder forwarder;
    private readonly ILoadBalancingPolicyFactory loadBalancing;
    private readonly IForwarderHttpClientFactory forwarderHttpClientFactory;
    private readonly ProxyLogger logger;

    public int Order => int.MinValue;

    public MirrorFunc(IServiceProvider serviceProvider, IHttpForwarder forwarder, ILoadBalancingPolicyFactory loadBalancing, IForwarderHttpClientFactory forwarderHttpClientFactory, ProxyLogger logger)
    {
        this.serviceProvider = serviceProvider;
        this.forwarder = forwarder;
        this.loadBalancing = loadBalancing;
        this.forwarderHttpClientFactory = forwarderHttpClientFactory;
        this.logger = logger;
    }

    public RequestDelegate Create(RouteConfig config, RequestDelegate next)
    {
        if (config.Metadata == null || !config.Metadata.TryGetValue("MirrorCluster", out var mirrorCluster) || string.IsNullOrWhiteSpace(mirrorCluster)) return next;

        return c => Mirror(c, mirrorCluster, next);
    }

    private async Task Mirror(HttpContext c, string mirrorCluster, RequestDelegate next)
    {
        var config = serviceProvider.GetRequiredService<IConfigSource<IProxyConfig>>();
        if (config.CurrentSnapshot == null || config.CurrentSnapshot.Clusters == null || !config.CurrentSnapshot.Clusters.TryGetValue(mirrorCluster, out var cluster) || cluster == null)
        {
            await next(c);
            return;
        }

        var originBody = c.Request.Body;
        using var buffer = new ReadBufferingStream(originBody);
        c.Request.Body = buffer;

        try
        {
            await next(c);
        }
        finally
        {
            c.Request.Body = buffer.BufferingStream;
            try
            {
                var proxyFeature = c.Features.GetRequiredFeature<IReverseProxyFeature>();
                var origin = proxyFeature.SelectedDestination;
                var selectedDestination = loadBalancing.PickDestination(proxyFeature, cluster);
                proxyFeature.SelectedDestination = origin;
                if (selectedDestination != null)
                {
                    cluster.InitHttp(forwarderHttpClientFactory);
                    await forwarder.SendAsync(c, proxyFeature, selectedDestination, cluster, new NonHttpTransformer(proxyFeature.Route.Transformer));
                }
            }
            catch (Exception ex)
            {
                logger.LogWarning(ex, "Mirror failed");
            }
            finally
            {
                c.Request.Body = originBody;
            }
        }
    }
}

所以说会再一次发送http 请求，请求body会临时暂存内存，所以无论内存还是请求延迟都会受到影响，特别body很大的请求

VKProxy 是使用c#开发的基于 Kestrel 实现 L4/L7的代理（感兴趣的同学烦请点个github小赞赞呢）