DataLocality for initially auto-applying DataCenter mount-option

[Ruakij]

DataLocality (inspired by Longhorn) allows instructing the storage-driver which volume-locations will be used or preferred in Pods to read & write.

It auto-sets mount-options based on the location a pod is scheduled in and the locality-option wanted.
The option can be set and overridden in Deployment, StorageClass and PersistentVolume.

Currently only 2 options exist:

• None changes nothing and is the default
• write_preferLocalDc sets the DataCenter-mount-option to the current Node-DataCenter, making writes local and reads wherever the data is.

---

Unfortunately Kubernetes doesnt allow grabbing node-labels, which contain well-known region-labels, and setting them as environment-variables.
The DownwardAPI is very limited in that regard. (see #40610)

Therefore i have modified the helm-chart to include a workaround using KubeMod based on this comment.
More explanations in deploy/helm/seaweed-csi-driver/values.yml in the key node.injectTopologyInfoFromNodeLabel

If this isnt wanted, feel free to remove it.

[chrislusf]

Does this need a document change?

[Ruakij]

It doesnt change existing stuff, but the new features should of course get proper documentation.
Some other stuff is also missing documentation, like available parameters for StorageClass or PersistentVolume.

I could start and create a first documentation how to use it and how to inject topology-info.
Think its a good idea to create new Readme-files and structure them?
(Am not a fan of the Github Wiki as its technically not "inside" the git-repo)

[chrislusf]

Yes, please help to document. Maybe just append a section to the main README.md file for now.

[Ruakij]

I have restructured the Readme a little bit, added an index as its getting quite long and have added documentation for DataLocality.

If you dont like the spaces between sections, feel free to remove them.