Munin is a useful tool for generating graphs of system performance. When setting it up on Debian and Ubuntu, it doesn’t automatically enable monitoring of Apache or MariaDB, but the reason why isn’t easy to spot.
Munin plugins are written in Perl, and the default Apache and MariaDB plugins rely on Perl libraries that aren’t installed by default in Ubuntu or Debian. Run apt install libcache-cache-perl for the Apache plugin, and apt install liblwp-protocol-https-perl for the MySQL/MariaDB plugin. Once those are installed, you can enable the plugins using munin-node-configure --shell | sh.