无法在工作中使用 c# 连接 mysql 服务器

Question

Why i failed to connect to a free cloud mysql DB using C# connector from Nuget in my work office PC while i can connect just fine to the same server using mysql CLI tool?

The message i get when i fail to connect is "Connect Timeout expired.".

I also tried on my PC at home and i can connect just fine using exactly the same C# code. Mysql CLI tool also work from home.

Could it be a firewall or other security measure in my work company network? Why it does not block the mysql CLI tool?

I also tried with a localhost mysql (using mysqld on port 51255) at work. I managed to connect using mysql CLI tool but got the same error as before on c# code.

EDIT1 - Code included

EDIT2 - localhost attempt

private async Task<string> ConnectDB()
{
    MySqlConnectionStringBuilder dbinfo = new MySqlConnectionStringBuilder
    {
        Server = "******",
        Port = ****,
        Database = "*****",
        UserID = "*****",
        Password = "*****",
    };
    using(MySqlConnection connection = new MySqlConnection(dbinfo.ConnectionString))
    {           
        try
        {
            await connection.OpenAsync();           
        }
        catch (MySqlException error)
        {                                               
            message = error.Message;                
        }
                
        if (connection.State == ConnectionState.Open)
        {                   
            message = "Success!";
        } 

    }
    return message;
}

Answer 1

We see the same C# code works at home, but not at the office. Therefore it's not the code; it must be something with the environment at the office. But you can connect at the office via the command line tools, so it's also not the corporate firewall, which would have a very hard time telling the the difference between the two.

What's left is something on the local PC at work. The local OS firewall and antivirus software both come to mind, and of the two the antivirus software sounds more suspect to me. One other option is DNS, where the DNS service at the office is resolving the host name for the database differently. But without more info this is just a guess. I suggest adding a lot more logging; right now we don't even know the full error message.

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As an additional note, it's not common and considered very poor practice to directly expose a database to the internet. Additionally, the application should be well-connected to the database. The definition for "well-connected" has changed over the years, but "public internet" is not going to count. Typically, if you most host the database in another location you will have a web API endpoint in front of the database, where the server for this API can be in the same location as the DB and therefore well-connected.