Random connection problems from Azure C# app to remote MySQL server

Question

I have an ASP.NET MVC web app that connects to a remote MySQL server (Ubuntu). I've never had any problems on my own Windows Server or localhost, but when I recently moved the app to Azure app services I get random connection errors (sometimes it works, sometimes not):

Unable to connect to any of the specified MySQL hosts.
at MySql.Data.MySqlClient.NativeDriver.Open() 
at MySql.Data.MySqlClient.Driver.Open() 
at MySql.Data.MySqlClient.Driver.Create(MySqlConnectionStringBuildersettings)
at MySql.Data.MySqlClient.MySqlConnection.Open()

There's no inner exception. My code looks a bit like:

using(var con = new MySqlConnection(connectionString))
{
  con.Open();
  using(var cmd = CreateCommand(sql, con))
  {
    cmd.Execute();        
  }
  con.Close();
}

Connection string looks like:

server=x.x.x.x;uid=xxx;pwd=xxx;database=xxx;Connection Timeout=10;Pooling=false;Protocol=socket;Port=3306;

This topic describes the same problem:

https://serverfault.com/questions/362216/mysql-completely-random-unable-to-connect

It has nothing to do with the firewall on the Ubuntu server, when a connection fails I don't even see incoming requests in the firewall. I also tried to use other settings in the connection string. Any ideas?

What do you mean by " random connection problem?" Do you mean it sometimes works correctly? Please [edit] your question to clarify. — O. Jones, Jun 19 '16 at 13:21
@OllieJones indeed, most of the time it works fine, but sometimes I got this connection error. — Marthijn, Jun 20 '16 at 06:30
Did you whitelist the IP addresses for your Azure App Service in your firewall? — ryanmcdonnell, Oct 19 '16 at 00:05

score 0 · Answer 1 · answered Jun 19 '16 at 13:37

protocol=socket tells your dot net instance to try to connect to a local MySQL server with UNIX domain sockets. But you're obviously trying to connect to a remote server with TCP/IP. Omitting protocol=socket from your connection string may help.

Does your Ubuntu server have a host name? If so, use it in place of an IP address. Is the IP route from Azure to your Ubuntu server stable, or does it go up and down? What happens if you ping your Ubuntu server from your Azure host?

A note: consider using tls (ssl) for this connection. The MySQL protocol without tls is not very secure.

Thanks for your reply, I will try your suggestions. I used a hostname before, but changed it to IP to make sure it wasn't a DNS problem. — Marthijn, Jun 20 '16 at 06:33

Random connection problems from Azure C# app to remote MySQL server

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