如何让Google VM开放外部HTTP连接？C# HttpListener配置问题排查

我正在Ubuntu 22.04的Google Cloud VM实例上搭建一个简单的C# HttpListener，用于监听外部连接。已经安装了dotnet并上传了源码，但在绑定地址时出现错误，无法实现外部访问的目标。

代码示例 #

Program.cs #

using System;
...
public class Program
{
    public const string ADDRESS = "http://VM_EXTERNAL_IP";
    public const int PORT = 80;
    public static Server server;
    static void Main(string[] args)
    {
        server = new Server(ADDRESS, PORT);
    }
}

Server.cs #

public class Server
{
    public string address;
    public int port;
    public Server(string address, int port)
    {
        HttpListener httpserver = new HttpListener();
        httpserver.Prefixes.Add(address + ":" + port + "/");

        httpserver.Start();

        Console.WriteLine("Listening on " + address + ":" + port + "/");
        while (httpserver.IsListening)
        {
            HandleHTTPConnections(httpserver);
        }
    }
}

错误信息 #

在执行httpserver.Prefixes.Add(address + ":" + port + "/");时抛出以下异常：

Unhandled exception. System.Net.HttpListenerException (99): Cannot assign requested address
   at System.Net.HttpEndPointManager.GetEPListener(String host, Int32 port, HttpListener listener, Boolean secure)
   at System.Net.HttpEndPointManager.AddPrefixInternal(String p, HttpListener listener)
   at System.Net.HttpEndPointManager.AddListener(HttpListener listener)

已尝试的方案 #

• 使用VM外部IP：ADDRESS = "http://34.118.16.122"，触发上述错误
• 使用VM内部IP：ADDRESS = "http://10.186.0.2"，触发相同错误
• 使用通用地址：ADDRESS = "http://+"，提示地址已被其他进程占用
• 使用localhost：ADDRESS = "http://localhost"，无报错但无法接受外部连接
• 尝试Google Cloud助手提供的SSH端口转发命令sudo ssh -L 80:localhost:22 user@EXTERNAL_IP_ADDRESS，收到"Permission denied"错误，且该操作对HTTP服务无实际帮助
• 添加GCP防火墙规则，允许任意内部IP的80端口HTTP连接，无效果

请问接下来应该尝试什么解决方法？

内容的提问来源于stack exchange，提问作者Mihai-Ionut FLOARES