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Merge pull request #20856 from willise/docs/affinity 

docs: reorganize topologyKey constraints
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Kubernetes Prow Robot 2020-05-09 07:51:50 -07:00 committed by GitHub
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content/en/docs/concepts/configuration/assign-pod-node.md
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@ -226,10 +226,11 @@ The legal operators for pod affinity and anti-affinity are `In`, `NotIn`, `Exist
In principle, the `topologyKey` can be any legal label-key. However,
for performance and security reasons, there are some constraints on topologyKey:
1. For affinity and for `requiredDuringSchedulingIgnoredDuringExecution` pod anti-affinity,
empty `topologyKey` is not allowed.
2. For `requiredDuringSchedulingIgnoredDuringExecution` pod anti-affinity, the admission controller `LimitPodHardAntiAffinityTopology` was introduced to limit `topologyKey` to `kubernetes.io/hostname`. If you want to make it available for custom topologies, you may modify the admission controller, or simply disable it.
3. For `preferredDuringSchedulingIgnoredDuringExecution` pod anti-affinity, empty `topologyKey` is not allowed.
1. For pod affinity, empty `topologyKey` is not allowed in both `requiredDuringSchedulingIgnoredDuringExecution`
and `preferredDuringSchedulingIgnoredDuringExecution`.
2. For pod anti-affinity, empty `topologyKey` is also not allowed in both `requiredDuringSchedulingIgnoredDuringExecution`
and `preferredDuringSchedulingIgnoredDuringExecution`.
3. For `requiredDuringSchedulingIgnoredDuringExecution` pod anti-affinity, the admission controller `LimitPodHardAntiAffinityTopology` was introduced to limit `topologyKey` to `kubernetes.io/hostname`. If you want to make it available for custom topologies, you may modify the admission controller, or simply disable it.
4. Except for the above cases, the `topologyKey` can be any legal label-key.
In addition to `labelSelector` and `topologyKey`, you can optionally specify a list `namespaces`