We can support topology detection for all drivers with a single
topology key by allowing different nodes to have the same topology
value. This makes the test a bit more generic and its configuration
simpler.
Drivers need to opt into the new test. Depending on how the driver
describes its behavior, the check can be more specific. Currently it
distinguishes between getting any kind of information about the
storage class (i.e. assuming that capacity is not exhausted) and
getting one object per node (for local storage). Discovering nodes
only works for CSI drivers.
The immediate usage of this new test is for csi-driver-host-path with
the deployment for distributed provisioning and storage capacity
tracking. Periodic kubernetes-csi Prow and pre-merge jobs can run this
test.
The alternative would have been to write a test that manages the
deployment of the csi-driver-host-path driver itself, i.e. use the E2E
manifests. But that would have implied duplicating the
deployments (in-tree and in csi-driver-host-path) and then changing
kubernetes-csi Prow jobs to somehow run for in-tree driver definition
with newer components, something that currently isn't done. The test
then also wouldn't be applicable to out-of-tree driver deployments.
Yet another alternative would be to create a separate E2E test suite
either in csi-driver-host-path or external-provisioner. The advantage
of such an approach is that the test can be written exactly for the
expected behavior of a deployment and thus be more precise than the
generic version of the test in k/k. But this again wouldn't be
reusable for other drivers and also a lot of work to set up as no such
E2E test suite currently exists.
