maG66

Install the plugin and check the Status URL Link. You can submit it to observo-monitoring.com to monitor it 24/7. 
– shell_exec must be available for cpu and memory 
– The plugin will install an open rest api 
– External servers can access this api to get performance stats 
– Services like observo-monitoring.com can give you an added value
<h3>Credits</h3>
<a href="https://www.observo-monitoring.com" title="Observo Monitoring" rel="nofollow ugc">Observo Monitoring</a>

Observo Monitoring

Monitor your Server Memory, Disk and CPU from external server

prouptime

Prouptime is service that monitors your wordpress blog or site. Prouptime checks your site every minute (or every five minutes) from its servers. If your site returns an error or is unreachable, prouptime will send you an email-alert.
You’ll also get statistics about your uptime and site-speed that you can view in your wordpress backend. You’ll also get these statistics by email once a week.

Prouptime – Uptime Monitoring & Alerts

Prouptime monitors your wordpress site and alerts you when it is unreachable or returns an error.

Observo Monitoring vs Prouptime – Uptime Monitoring & Alerts