Postgres Config postgresql.conf : ssl = on log_connections=on Check default connection is SSL Ensure config.php $CFG->dboptions does not have 'ssl' entry Request any page from the site Confirm that database log (usually /var/log/postgresql/postgresql-nn-main.log has a line similar to: connection authorized: user=moodle database=moodle SSL enabled (protocol=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384, bits=256) Check verify-full Ensure Postgres does not have CA signed certificate, eg self-signed certigicate in postgresql.conf : ssl_cert_file='/etc/ssl/certs/ssl-cert-snakeoil.pem' Moodle config.php $CFG->dboptions : Set 'ssl' => 'verify-full' Request any page from the site Confirm that Error: Database connection failed is displayed MySQL (MariaDB) Config any mysql *.cnf : Create a self-signed certificate ( https://mariadb.com/kb/en/certificate-creation-with-openssl/ ) and add to the config: [mysqld] ssl-ca = /etc/mysql/ssl/ca.pem ssl-cert = /etc/mysql/ssl/server-cert.pem ssl-key = /etc/mysql/ssl/server-key.pem require_secure_transport = on Check no ssl config Ensure config.php $CFG->dboptions does not have 'ssl' entry Request any page from the site Confirm that Error: Database connection failed is displayed Check required Moodle config.php $CFG->dboptions : Set 'ssl' => 'require' Moodle config.php $CFG->dbhost : Set to either FQDN from the self-signed certificate, or database server IP address Request any page from the site Confirm that Error: Database connection failed is not displayed{ } Check verify-full { } Moodle config.php $CFG->dboptions : Set 'ssl' => 'verify-full' Request any page from the site Confirm that Error: Database connection failed is displayed Note : mysqli will do the server certificate validation if the dbhost is a name, and not do it if it is an IP address. That cannot be changed with any option. CA signed certificate If you also have a CA signed certificate, you can (for both databases)   Change config options (see corresponding Config sections above) to point to that certificate Request any page from the site Confirm that Error: Database connection failed is not displayed