You cannot assign applications (or pods) directly to nodes in OpenShift. This is supposed to be an administrator decision, not a developer one.
Without giving details, the administrator would assign labels to the nodes, and a node selector to the project. The selector controls which nodes can run applications / pods from this project. It is supposed to be invisible to developers.
The OpenShift administrator guide provides details on doing this, look on the scheduling section.
s, Fernando Lozano