TAS: respect node taints when the lowest hierarchy level is node

[mimowo]

What would you like to be added:

Respect node taints when scheduling by TAS when the lowest hierarchy level is kubernetes.io/hostname.

Why is this needed:

Some users may want to taint a node and exclude it from TAS. However, we still should include the tainted notes for which the workload has tolerations.

[mimowo]

cc @PBundyra @tenzen-y
/assign

[tenzen-y]

I discussed this with @mimowo offline.
Technically, we can check taints at all levels.
But, in that case, we need to traverse all hierarchical taints.
So, we support only the lowest hierarchy-level taints.

[mimowo]

A relatively simple approach for supporting taints for any Topology levels, I discussed with @PBundyra yesterday, is to introduce a "virtual" level for nodes, even if not specified directly by the user in the Topology object. Still, it adds a bit of complexity, so I want to deliver this in two parts:

1. respect taints if the lowest level is kubernetes.io/hostname
2. respect taints for any topology by introducing the "virtual" level corresponding to kubernetes.io/hostname

The priority of (2.) is lower, but it should be simple so I will try to fit both into 0.10

[mimowo]

After consulting this with @mwielgus we decided to defer this decision / support for later. I open KEP update to capture the need to handle topologies without hostname better: #3681

[mimowo]

/close
The main issue is addressed, we will re-consider the options when there is no kubernetes.io/hostname the last level post 0.10, proposed KEP update: #3681

[k8s-ci-robot]

@mimowo: Closing this issue.

In response to this:

/close
The main issue is addressed, we will re-consider the options when there is no kubernetes.io/hostname the last level post 0.10, proposed KEP update: #3681

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