1、使用HttpClientFactory工厂；

2、Startup里ConfigureServices添加HttpClient的具体的客户端服务；（注册到DI容器 ）

services.AddHttpClient("SystemService", c =>
{
c.BaseAddress = new Uri(Configuration["ApiConfig:SystemService"]);
c.Timeout = TimeSpan.FromSeconds(30);
});

3、增加默认连接数和启用保活机制

在Program的Main方法里添加 

  //增加保活机制，表明连接为长连接
  client.DefaultRequestHeaders.Connection.Add("keep-alive");
  
  //启用保活机制（保持活动超时设置为 2 小时，并将保持活动间隔设置为 1 秒。）
  ServicePointManager.SetTcpKeepAlive(true, 7200000, 1000);
  
   //默认连接数限制为2，增加连接数限制
  ServicePointManager.DefaultConnectionLimit = 512;

4、尝试使用Socket通信连接

var client = new HttpClient(new SocketsHttpHandler()
{
    //考虑忽略使用代理
    UseProxy = false,
    //考虑增加连接数配置
    MaxConnectionsPerServer = 100,
    //考虑忽略重定向响应
    AllowAutoRedirect = false,
    //考虑忽略SSL证书验证
    SslOptions = new SslClientAuthenticationOptions()
    {
        RemoteCertificateValidationCallback = (sender, certificate, chain, sslPolicyErrors) => true
    },
    //考虑数据压缩设置
    AutomaticDecompression = DecompressionMethods.Deflate | DecompressionMethods.GZip,
  })
  {
      BaseAddress = new Uri(""),
      Timeout = TimeSpan.FromSeconds(30),
  };

 

new HttpClient(new SocketsHttpHandler()看第一句代码。