One of the things that is stressed in the DevOps Handbook, is the need for telemetry, or monitoring of services. For services you run on your own infrastructure, there are several tools that can be used for this, such as SCOM, Zabbix, and Splunk. When you don’t have an infrastructure that supports these tools, however, you need to find a different approach.
I’ve been using Pingdom since about 2011 to monitor uptime for this site, and this has generally been working well. In March of 2018, I added Uptime Robot to the mix, which offers more checks, across more sites, at lower price points. This has let me implement additional checks, as well as monitor the other sites I manage, both of which have served me well. Though both tools work well, for my needs Uptime Robot works far better, offering more checks at the same cost.