Check your database connection settings, ensure your database server is running, and verify network accessibility between your application and the database.

If your Node.js application fails to connect to a database, it can severely disrupt functionality, so addressing the issue promptly is vital. Start by checking your database connection settings; ensure that the host, port, username, password, and database name are all correct in your connection string. If you're using environment variables to manage these settings, verify that they are correctly configured and accessible to your application. Ensure your database server is running; you can check this by trying to connect via a database client or command-line tool. Verify network accessibility between your application and the database; this may involve checking firewall rules or network settings that could be blocking access. If you’re using a cloud database service, ensure that any necessary security groups or access controls are set up to allow connections from your application’s IP address. Implement error handling in your database connection code to capture and log specific errors, as these can provide valuable clues about what went wrong. Additionally, consider testing your connection settings in a local or development environment to rule out environmental issues. By systematically addressing these areas, you can effectively troubleshoot and resolve database connection issues in your Node.js application.