Error connecting to DB in /wp-includes/wp-db.php on line 1538 [closed]

new in wordpress world.

My wordpress page keeps failing. It works from time to time, meaning refreshing sometimes offer the page, others it offers the Error establishing a database connection page.

Checking the wp-content/debug.log it says:

PHP Warning:  mysqli_real_connect(): php_network_getaddresses: getaddrinfo failed: No address associated with hostname in /www/wp-includes/wp-db.php on line 1538

As far as I know, this file is a wordpress one so no one has touched it.

Any ideas from where it can come?
Any experience or tips on what to do?

Are you running on Ubuntu? Library libc was recently updated, and if you have unattended-upgrades enabled, that will be the cause. A restart of PHP-FPM, Apache, Nginx will solve it. Even better if you could reboot the entire server to be sure.

libc is the C implementation for Linux, and PHP runs on C.