nodejs mysql Error: Connection lost The server closed the connection

Try to use this code to handle server disconnect:

var db_config = {
  host: 'localhost',
    user: 'root',
    password: '',
    database: 'example'
};

var connection;

function handleDisconnect() {
  connection = mysql.createConnection(db_config); // Recreate the connection, since
                                                  // the old one cannot be reused.

  connection.connect(function(err) {              // The server is either down
    if(err) {                                     // or restarting (takes a while sometimes).
      console.log('error when connecting to db:', err);
      setTimeout(handleDisconnect, 2000); // We introduce a delay before attempting to reconnect,
    }                                     // to avoid a hot loop, and to allow our node script to
  });                                     // process asynchronous requests in the meantime.
                                          // If you're also serving http, display a 503 error.
  connection.on('error', function(err) {
    console.log('db error', err);
    if(err.code === 'PROTOCOL_CONNECTION_LOST') { // Connection to the MySQL server is usually
      handleDisconnect();                         // lost due to either server restart, or a
    } else {                                      // connnection idle timeout (the wait_timeout
      throw err;                                  // server variable configures this)
    }
  });
}

handleDisconnect();

In your code i am missing the parts after connection = mysql.createConnection(db_config);

To simulate a dropped connection try

connection.destroy();

More information here: https://github.com/felixge/node-mysql/blob/master/Readme.md#terminating-connections

I do not recall my original use case for this mechanism. Nowadays, I cannot think of any valid use case.

Your client should be able to detect when the connection is lost and allow you to re-create the connection. If it important that part of program logic is executed using the same connection, then use transactions.

tl;dr; Do not use this method.

A pragmatic solution is to force MySQL to keep the connection alive:

setInterval(function () {
    db.query('SELECT 1');
}, 5000);

I prefer this solution to connection pool and handling disconnect because it does not require to structure your code in a way thats aware of connection presence. Making a query every 5 seconds ensures that the connection will remain alive and PROTOCOL_CONNECTION_LOST does not occur.

Furthermore, this method ensures that you are keeping the same connection alive, as opposed to re-connecting. This is important. Consider what would happen if your script relied on LAST_INSERT_ID() and mysql connection have been reset without you being aware about it?

However, this only ensures that connection time out (wait_timeout and interactive_timeout) does not occur. It will fail, as expected, in all others scenarios. Therefore, make sure to handle other errors.

better solution is to use the pool - it will handle this for you.

const pool = mysql.createPool({
  host: 'localhost',
  user: '--',
  database: '---',
  password: '----'
});

// ... later
pool.query('select 1 + 1', (err, rows) => { /* */ });

https://github.com/sidorares/node-mysql2/issues/836