Found that the entire web server was not down, only mariadb (what used to be mysql). MariaDB is necessary to our site and any site which uses WordPress or other content management engines.
I’ve added a script to crontab now that checks once a minute and restarts it if it dies. But there is no indication in the logs of what caused it to die. The only errors logged where an attempt to access a non-existent database, but doing that does not cause MariaDB to die so I still do not know what did.