It can be helpful to setup alerts for droplets in DigitalOcean which can notify you if system resources exceed a certain threshold.
To do that, first install the DigitalOcean Monitoring Metrics Agent at the time of creating droplets or it can be installed later. A detailed guide for both can be found here.
After it is setup, login to your account and select Alert Policies from the Create menu.
Then set the alert parameters as needed and select the droplet for which alerts are to be enabled.
There are different parameters for which these alerts can be set like CPU, bandwidth, disk I/O, memory and so on.
By default, you will get the alerts through email but you can also use Slack for that.
Finally, add the Alert Policy by clicking on Create Alert Policy.
This is a helpful feature to monitor droplets and keep them optimized.