How to reliably run Rancher Server inside it's Cattle environment

Is it reliable and safe to run Rancher Server in it’s own environment? (Cattle or Kubernetes by Rancher 2)

I was not able to find a document about it, all docs describe just running it stand alone in a plain Docker.

No, you cannot run the server (or it’s database) inside itself properly. The server or db for a different unrelated installation would be ok though.