How to Resolve Node.js MySQL 'Connection lost: The server closed the connection' Errors?

Node.js MySQL: Resolving "Connection lost: The server closed the connection" Error

When establishing connections to MySQL databases using Node.js, it's possible to encounter an error stating "Connection lost: The server closed the connection." This error typically occurs during periods like 12:00 to 2:00, when the TCP connection is interrupted by the server.

Solution 1: Automatic Reconnection Handling

To handle this error automatically, implement the following code:

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

var connection;

function handleDisconnect() {
  connection = mysql.createConnection(db_config); 
  connection.connect(function(err) { 
    if(err) { 
      console.log('error when connecting to db:', err);
      setTimeout(handleDisconnect, 2000); 
    } 
  }); 
  connection.on('error', function(err) {
    console.log('db error', err);
    if(err.code === 'PROTOCOL_CONNECTION_LOST') { 
      handleDisconnect(); 
    } else { 
      throw err; 
    }
  });
}

handleDisconnect();

In this code, a connection is established with the MySQL server. If the connection is lost due to a server restart or an idle timeout, the handleDisconnect() function is called, which re-establishes the connection.

Solution 2: Manual Reconnection

In the provided code, you have implemented part of the automatic reconnection mechanism, but there's a missing portion after the line connection = mysql.createConnection(kf_config);. The following code completes the implementation:

connection.connect(function(err) {
  if (err) {
    console.log("Error connecting to KFC: " + err);
  } else {
    console.log("KF connected!");
  }
});

You should also register an error listener on the connection object to automatically handle connection lost events. For example:

connection.on('error', function(err) {
  if (err.code === 'PROTOCOL_CONNECTION_LOST') {
    console.log("KF connection lost. Reconnecting...");
    handleKFDisconnect();
  } else {
    throw err;
  }
});

By following these steps, you can ensure that your Node.js MySQL application handles connection loss gracefully and automatically reestablishes the connection.

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