etcd is the foundation of Kubernetes. So having a good set of alerts for it is important. We wrote this blog post and creating alerting rules for it and provided a base set at the end.

Further sources of important metrics in the Prometheus format are the Kubelet and cAdvisor, API servers, and the fairly new kube-state-metrics. For those, I'm not aware of any public alerting rule sets as for etcd, unfortunately.

Generally, you want to ensure that the components as applications work flawlessly, e.g:

• Are my kubelets/API servers running/reachable? (up metric)
• Are their response latency and error rates within bounds?
• Can the API servers reach etcd?

Then there's the Kubernetes business logic aspect, e.g:

• Are there pods that have been in non-ready/crashloop state forever?
• Do I have enough CPU/memory capacity in my cluster?
• Are my deployment replica expectations fulfilled?

That's no drop-in solution unfortunately, but writing alerting rules roughly covering the scope of the above examples should get you quite far.