According to the document, KubeSpawner will use randomly allocated port.
I deployed zero-to-jupyterhub-k8s (hostNetwork:true set for spark) and got error when login some users:
[Warning] 0/3 nodes are available: 1 node(s) had taints that the pod didn't tolerate, 2 Insufficient memory, 2 node(s) didn't have free ports for the requested pod ports.

That's because KubeSpawner always use port 8888 instead of random port. https://github.com/jupyterhub/kubespawner/blob/master/kubespawner/spawner.py#L145

https://jupyterhub-kubespawner.readthedocs.io/en/latest/spawner.html

config c.KubeSpawner.port = Int(0)
The port for single-user servers to listen on.

Defaults to 0, which uses a randomly allocated port number each time.

If set to a non-zero value, all Spawners will use the same port, which only makes sense if each server is on a different address, e.g. in containers.

New in version 0.7.