https://www.youtube.com/watch?v=dbF61BCEU9U 

https://www.devopsonline.co.uk/the-importance-of-monitoring-in-devops/

https://medium.com/devopscurry/understanding-continuous-monitoring-in-devops-f6695b004e3b 

https://www.youtube.com/watch?v=Zu53QQuYqJ0 

https://www.youtube.com/watch?v=4t71iv_9t_4

nagios 
zabbbix
prometheus - https://www.youtube.com/watch?v=h4Sl21AKiDg 
https://www.youtube.com/watch?v=5o37CGlNLr8