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Added discussion regarding PV NodeAffinity

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Cheng Xing 2018-04-19 11:54:58 -07:00
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contributors/design-proposals/storage/container-storage-interface.md
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@ -414,6 +414,97 @@ The alternative is invalid because the driver name could be up to 63 characters
Because CSI topology values only contain the topology name (`rack`) and topology value (`rack1`), the driver name and the constant prefix must be prepended to the label as part of the provisioner's topology translation step.
#### Topology Representation in PersistentVolume Objects
There exists multiple ways to represent a single topology as NodeAffinity. For example, suppose a `CreateVolumeResponse` contains the following accessible topology:
```yaml
- zone: "a"
rack: "1"
- zone: "b"
rack: "1"
- zone: "b"
rack: "2"
```
There are at least 3 ways to represent this in NodeAffinity (excluding `nodeAffinity`, `required`, and `nodeSelectorTerms` for simplicity):
Form 1 - `values` contain exactly 1 element.
```yaml
- matchExpressions:
- key: zone
operator: In
values:
- "a"
- key: rack
operator: In
values:
- "1"
- matchExpressions:
- key: zone
operator: In
values:
- "b"
- key: rack
operator: In
values:
- "1"
- matchExpressions:
- key: zone
operator: In
values:
- "b"
- key: rack
operator: In
values:
- "2"
```
Form 2 - Reduced by `rack`.
```yaml
- matchExpressions:
- key: zone
operator: In
values:
- "a"
- "b"
- key: rack
operator: In
values:
- "1"
- matchExpressions:
- key: zone
operator: In
values:
- "b"
- key: rack
operator: In
values:
- "2"
```
Form 3 - Reduced by `zone`.
```yaml
- matchExpressions:
- key: zone
operator: In
values:
- "a"
- key: rack
operator: In
values:
- "1"
- matchExpressions:
- key: zone
operator: In
values:
- "b"
- key: rack
operator: In
values:
- "1"
- "2"
```
The provisioner will always choose Form 1, i.e. all `values` will have at most 1 element. Reduction logic could be added in future versions to arbitrarily choose a valid and simpler form like Forms 2 & 3.
### Example Walkthrough
#### Provisioning Volumes