Nginx Serverload full - how to find out which cause?

I have a VPS at vultr 2GB RAM install centminmod 123.08stable.
I install fail2ban and redis cached on that server too.
I just install only 1 wordpress site on that server and traffic is too low (about 50-150 visitor a DAY), but sometime, my server show that it load full, something like this (i use nodequery to monitor):

I also try to running a joomla site with lower traffic (<100 visitor a day), but still get that notice. I set notice will system load over 70%.

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Server: Biên Thùy - Chia sẻ kiến thức về joomla, wordpress, VPS
Last Update: 2017-08-16 08:27:39
Alert Trigger: 2017-08-16 08:28:01

Average: 4.95 1.40 0.51

System Load: 100%
Ram Usage: 34%
Disk Usage: 9%

mysqld 1.8% 180.93 MB mysql (1)
php-fpm 0.6% 279.33 MB nginx (6)
redis-server 0.2% 13.07 MB redis (1)
php-fpm 0% 44.28 MB root (1)
tuned 0% 15 MB root (1)
dhclient 0% 12.88 MB root (1)
fail2ban-server 0% 11.05 MB root (1)
nginx 0% 10.39 MB nginx (2)
polkitd 0% 8.97 MB polkitd (1)
crond 0% 3.88 MB root (2)

Could you please help me how to find out which one cause this high load?
Thank you so much

• CentOS Version: CentOS 7.5 64bit ?
• Centmin Mod Version Installed: 123.08stable
  
• Nginx Version Installed: 1.12.1
• PHP Version Installed: 7.1.8
• MariaDB MySQL Version Installed: 10.5
• When was last time updated Centmin Mod code base ? :
  
• Persistent Config:
  

 

It have been months, so i'm trying other script (like hocvps, vpsim...) and install LEMP manual to see if it happen again (over load) but i want to find out which one cause that to fix.