I am talking about the services which let you monitor the status of a website whether the website is up and operational or down or under heavy load.
how do they work under the hood?
for example:
I am building something similar for monitoring my web projects.
A webservice can be passively monitored.
So, the status system would check DNS records, ping IP addresses and do a get request to check it gets a 200 response. Further metrics like ping and response times could be monitored and report if they are too high, indicating heavy load.
Uptime Kuma is a foss project that is popular amongst self-hosters.
A webservice can actively report for monitoring. So a webservice would monitor its CPU/RAM/network usage, database connections, cache misses, stuff like that. If you are load balancing, then an additional service would be needed to aggregate the results of all these and decide when its degraded performance due to too many nodes being offline/overloaded.
Things like prometheus, netdata can do the metrics.
Or, like how i think a lot of these work, just report it manually. Ive seen quite a few companies that report green status, despite having fairly huge issues