Java 中 socket 网络编程的问题？

Question

这里我使用的是 sunny-ngrok 的免费域名，连接端口都没有问题，运行也是服务端先运行再运行客户端。但是为什么会提示连接失败呢？

import org.junit.Test;

import java.io.*;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;

/**
 * 实现 TCP 网络通讯
 *      客户端发送文件给服务端，服务端保存文件至本地
 */
public class TCPTestTwo {

    /*
        客户端
     */
    @Test
    public void client() {
        Socket socket = null;
        OutputStream os = null;
        BufferedInputStream bis = null;
        try {
            socket = new Socket(InetAddress.getByName("64.69.43.110"), 8809);
            os = socket.getOutputStream();
            bis = new BufferedInputStream(new FileInputStream(new File("test.png")));
            byte[] bytes = new byte[1024];
            int len;
            while ((len = bis.read(bytes)) != -1) {
                os.write(bytes, 0, len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {

            if (bis != null) {
                try {
                    bis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            if (os != null) {
                try {
                    os.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (socket != null) {
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    /*
        服务端
     */
    @Test
    public void server() {
        ServerSocket serverSocket = null;
        Socket socket = null;
        InputStream is = null;
        BufferedOutputStream bos = null;
        try {
            serverSocket = new ServerSocket(8809);
            socket = serverSocket.accept();
            is = socket.getInputStream();
            bos = new BufferedOutputStream(new FileOutputStream(new File("test5.png")));
            byte[] bytes = new byte[1024];
            int len;
            while ((len = is.read(bytes)) != -1) {
                bos.write(bytes, 0, len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (bos != null) {
                try {
                    bos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (socket != null) {
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (serverSocket != null) {
                try {
                    serverSocket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }


    }
}