As per the announcement the stable tag should be the one used to upgrade to latest stable version however the tag is not there:
https://hub.docker.com/r/rancher/rancher/tags/
➜ ~ docker pull rancher/rancher:stable
Error response from daemon: manifest for rancher/rancher:stable not found
Same goes for :master
Here https://rancher.com/docs/rancher/v2.x/en/installation/server-installation/single-node-install/ the code is also wrong.
It tells you to use latest while stable is the right one
Image name changed from “rancher/server” to “rancher/rancher”.
Source : https://github.com/rancher/rancher/issues/13383#issuecomment-387733103
rancher/rancher:stable is now available. We held off on tagging v2.0.0 to ensure there were no showstopper horrible bugs.
Image is inentionally rancher/rancher.
rancher/server is for the 1.x line