Error when accesing MySQL database remotely using public IP

Question

I have a MySQL database. My friend is trying to access it from a different computer using my public IP.

This is the program he used to test the connection:

public class Main {
    public static void main(String args[]) {

        String url = "jdbc:mysql://IPadresss:3307/javabase";
        String username = "bob";
        String password = "bob";
        Properties properties = new Properties();
        properties.setProperty("bob", "bob");
        properties.setProperty("bob", "bob");
        properties.setProperty("useSSL", "false");
        properties.setProperty("autoReconnect", "true");

        System.out.println("Connecting database...");

        try (Connection connection = DriverManager.getConnection(url, properties)) {
            System.out.println("Database connected!");
        } catch (SQLException e) {
            throw new IllegalStateException("Cannot connect the database!", e);
        }
    }
}

This is the error my friend, who is the client, gets:

Connecting database...
Exception in thread "main" java.lang.IllegalStateException: Cannot connect the database!
 at SQLConnector.Main.main(Main.java:23)
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.
 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
 at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
 at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
 at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
 at com.mysql.jdbc.Util.getInstance(Util.java:408)
 at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:918)
 at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:897)
 at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:886)
 at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:860)
 at com.mysql.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:2163)
 at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2088)
 at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:806)
 at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
 at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
 at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
 at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
 at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:410)
 at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:328)
 at java.sql.DriverManager.getConnection(DriverManager.java:664)
 at java.sql.DriverManager.getConnection(DriverManager.java:208)
 at SQLConnector.Main.main(Main.java:20)
Caused by: java.sql.SQLException: Access denied for user ''@'Freinds ip' (using password: NO)
 at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:964)
 at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3970)
 at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3906)
 at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:873)
 at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1710)
 at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1226)
 at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2253)
 at com.mysql.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:2104)
 ... 13 more

Please help me find out what is wrong with my method of connecting to the server, I have remotely given privileges to my friend (user "bob").

If you put a mysql database on a public IP, even assuming nobody manages to figure out your usernames and passwords, they can very, very easily DOS attack your sql database and bring it down. So open the firewall only to valid client IPs. Or use a more secure approach ( I recommend ssh tunnel). People _will_ find a world accessible open service on any port. — erik258, Jan 06 '17 at 17:18
The stack trace appears to show that the problem arises from MySQL access control: "Access denied for user ''@'Freinds ip' (using password: NO)". The best solution is probably to create a database user for your friend, with password, and to grant that user access to the database, either from all machines or (better) specifically from the one he's using. — John Bollinger, Jan 06 '17 at 17:21

score 0 · Answer 1 · edited Jun 20 '20 at 09:12

So, you have the following error:

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure java.net.ConnectException: Connection refused

This could happen for a variety of reasons, and I'm quoting from this answer

If you get a SQLException: Connection refused or Connection timed out or a MySQL specific CommunicationsException: Communications link failure, then it means that the DB isn't reachable at all.

This can have one or more of the following causes:

IP address or hostname in JDBC URL is wrong.

Hostname in JDBC URL is not recognized by local DNS server.

Port number is missing or wrong in JDBC URL. [Assuming the one you mentioned is correct]

DB server is down.

DB server doesn't accept TCP/IP connections.

DB server has run out of connections.

Something in between Java and DB is blocking connections, e.g. a firewall or proxy.

To solve the one or the other, follow the following advice:

Verify and test them with ping.

Refresh DNS or use IP address in JDBC URL instead.

Verify it based on my.cnf of MySQL DB.

Start the DB.

Verify if mysqld is started without the --skip-networking option.

Restart the DB and fix your code accordingly that it closes connections in finally.

Disable firewall and/or configure

firewall/proxy to allow/forward the port.

Error when accesing MySQL database remotely using public IP

1 Answers1