for on-prem continuous monitoring i use a few things, mostly PRTG and telegraf/influx.

i use graylog, but don't have any alerting. it's just handy for centralizing sys/app logs.

i also have Security Onion set up and ingesting traffic but i don't really do anything with it yet.

For a while, I had some basic monitors configured in Netdata that would push alerts to PagerDuty.

Lately though, I've scaled back so much in the HomeLab that using Netdata doesn't make sense like it used to  Hardware alerts built in to True NAS work for monitoring and UptimeKuma takes care of service monitoring for the handful of things that do run all the time.

I definitely agree on the fronts of monitoring being on-premises. This has definitely been my preference for years now, but definitely exploring some of the options out there. It piqued my curiosity that Netdata now has a home lab license as well that looks interesting, especially since you get unlimited nodes it looks like but definitely will report my findings back on that!

I've used a couple of different monitoring tools in the past (PRTG, etc.), but always found the free versions too limiting.

My only active cloud-based monitor is currently UptimeRobot(.com), a service that monitors Websites on a five-minute time interval. It monitors the handful of Websites I host as well as my Plex servers.

Locally, I have a vRealize Log Insight (now Aria Operations for Logs) instance for syslog and Windows event recording, but it's not set to alert me on anything. One of my Synology NASes also does syslog.

I have a project (it's on my project list, I swear!) to implement Check_MK, which is an on-premise monitoring solution with a community-supported free version. We use it at work and it's very comprehensive, alerting on state changes (example: green to critical or vice versa) down to the service level. It monitors everything from vCenter services to Horizon services to disk space usage across hosts to our Log Insight clusters. Admittedly, I haven't gotten very far with Check_MK thus far at home.

I realize you asked about cloud-based solutions, but I have a preference for on-premises solutions given the choice. Internet connectivity for most of us is too fragile a thing to rely on being available one hundred percent of the time, and a monitoring solution should strive for that tier of availability.