OneUptime (https://github.com/oneuptime/oneuptime) is the open-source alternative to StausPage.io + UptimeRobot + PagerDuty. We’re working on adding APM functionalities to it to make it closer to an open-source alternative to data dog. It’s 100% free and you can self-host it on your VM / server.

UPDATE: Docker Compose file is in the repo and Its now on ArtifactHub: https://artifacthub.io/packages/helm/oneuptime/oneuptime and you can try it out on your K8s clusters.
Looking forward to hearing what you all think!