"No database connection" error in ProcessWire database component

Answer

To distinguish a DNS/network failure from an authentication error, temporarily wrap ProcessWire’s PDO connection in a try/catch block that logs the PDOException details before re‑throwing or displaying a debug message.

Likely explanation

The generic “No database connection” fatal error is thrown when the PDO constructor fails; the underlying PDOException contains the SQLSTATE code and message that tell you whether the problem is a connection‑refused/DNS issue (e.g., SQLSTATE[HY000][2002]) or bad credentials (SQLSTATE[28000][1045]).

Confirmed facts

• ProcessWire uses PDO with the mysql driver; the error originates from the PDO constructor in wire/core/ProcessWire.php (or the database init in site/config.php).
• The required PHP extension is pdo_mysql (often bundled as php‑pdo_mysql or enabled via extension=pdo_mysql).
• The driver must match the client library version used by the remote MySQL/MariaDB server (mysqlnd 5.0.12+ for modern password hashing).

Steps to capture the exception

1. Make a backup of site/config.php.
2. Edit the file and locate the lines that create the PDO instance (usually $db = new PDO(...); or within wire/core/ProcessWire.php).
3. Wrap that instantiation in a try/catch block:

try {
    $db = new PDO($dsn, $user, $pass, $options);
} catch (PDOException $e) {
    // Log details – adjust path as needed
    error_log('ProcessWire PDO error: '.$e->getMessage().' (SQLSTATE: '.$e->getCode().')');
    // Optionally output for debugging (remove in production)
    echo '
PDO error: '.$e->getMessage().' (SQLSTATE: '.$e->getCode().')
';
    throw $e; // re‑throw to keep original fatal behaviour if desired
}


Reload the site; check the PHP error log (or the temporary output) for the SQLSTATE and message.
Interpret the code: 2002 → connection refused/DNS; 1045 → bad username/password; other codes point to SSL or server version issues.
Once the cause is identified, revert the try/catch changes (or keep logging only) to avoid exposing credentials.

Verifying the PDO driver

Run php -m | grep pdo_mysql on the production host; you should see pdo_mysql in the list.
Or create a phpinfo() page and confirm the PDO section shows PDO drivers => mysql.
Ensure the extension is enabled in php.ini (extension=pdo_mysql) and that the MySQL client library (mysqlnd) version is compatible with the remote server (run php -r "echo phpversion('pdo_mysql');" to see the driver version).

Missing diagnostic detail: Can you confirm whether the production host can reach the remote MySQL server on port 3306 (e.g., via telnet  3306 or nc -zv  3306)? If the host cannot reach the server, the issue is network/DNS‑related; if it can, focus on credentials or driver compatibility.