OpenShift configuration management As far as I can tell, reading the OpenShift documentation, including https://github.com/openshift/training/, the officially published "standard" way to manage OpenShift configuration (about their objects like services, build config etc.) is to simply use oc or the web console and "do it". They do not seem to document/suggest a standard way to keep this configuration, i.e. the YAML or JSON representation that you see in the web console or in oc edit in, say, a git repository.

Would you say that most projects (that you witnessed or know about) work this way, i.e., just keeping the config inside OpenShift? Or are there established standards, to have this outside of OpenShift itself?

I noticed that there is a 3rd party OpenShift ansible module on github, but am not quite sure how proven/established that is.
AFAIK neither OpenShift nor Kubernetes itself allow you to externalize services configuration. You should have a bunch of yml/json files somewhere and control their deployment/configuration using CLI tools.

But there is Rancher which in version 2.0 allow us to import external Kubernetes clusters and manage them as Rancher's own environments. 

Description of how this could be done with Rancher you can find here.

FYI: Rancher 2.0 is slowly moving to Beta so it might take time for you to use it in your activities.