Let me start by saying that my web-host advised me to re-install the VPS when I had this problem (it was an newly installed one so there was no problem with re-installing it). Therefore I can not give more information then what I will give in this post. I do not want an solution, just some pointer to what I could try if I get this problem again.
After installing DirectAdmin on my VPS and migrating a domain to this server I installed csf with lfd. After installation I left all the configurations the same, except for the SSH port. I changed that to another port.
When a few days had passed my server began to randomly start httpd processes and the memory use started to increase exponentially. Each time I would reboot the server, it would take about 10 minutes before it happened again. Stopping the httpd daemon did not help, as the daemon would automatically start again.
Also, the mysqld process would take up about 2.4GB of RAM, the combined httpd processes 1.6GB (the server has 4GB of RAM). So the server would become unavailable.
I checked the Apache logs and server logs but could not find anything out of the ordinary.
What I would really like to know if anyone else has had this problem. If so, did you find an solution for it. What was the solution? I would like to know this for future reference. And maybe someone else will find it helpful too.