This isn’t really a Discourse issue, but I’ve decided that it’s time that I have something more formal in place to know when a site is down than to happen to notice or get an email from someone.
I’ve seen pingdom and uptimerobot.
Well, and here’s this: The Best Website Monitoring Services of 2017 | PCMag.com. But most of those cost 10-100x what would make sense for me. See also Best Website Monitoring Software | 2017 Reviews of the Most Popular Systems for a list that seems too long to be useful; well, you can filter by various factors.