Kubernetes microservices monitoring & alerting
I would caution against trying to build your own in-house monitoring solution. There are considerable drawbacks to that approach.
If all you need is external service HTTP health checks, then many existing monitoring solutions will do fine. You can either install a traditional IT solution like Zabbix or Nagios. Or use a SAS like Datadog and others.
There are also blackbox extensions for Prometheus, which is very popular among K8s users.
Many of these options have a learning curve of some steepness.