Investigate implementing new learner role for etcd members

[superseb]

An operator should do the minimum amount of work possible to add a new learner node. member add --learner command to add a new learner, which joins cluster as a non-voting member but still receives all data from leader

https://etcd.io/docs/v3.4.0/learning/design-learner/

[stale]

This issue/PR has been automatically marked as stale because it has not had activity (commit/comment/label) for 60 days. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.

[zmedico]

@superseb can we revisit this now? EtcdLearnerMode was added to kubeadm as an alpha feature in v1.27, and promoted to beta and enabled by default in v1.29.

[superseb]

Yep, I still think this is valuable.

[github-actions]

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[zmedico]

I am using an aws autoscaling group to manage a group of rke etcd nodes. The kubernetes documentation for scaling out etcd clusters recommends against using auto scaling groups. I'm not sure if this recommendation applies to an autoscaling group that is typically static in size (size only varies during node replacement). Anyway, I hope that the etcd learner role can serve as a way to improve support for replacing etcd nodes via auto scaling groups.

[github-actions]

This repository uses an automated workflow to automatically label issues which have not had any activity (commit/comment/label) for 60 days. This helps us manage the community issues better. If the issue is still relevant, please add a comment to the issue so the workflow can remove the label and we know it is still valid. If it is no longer relevant (or possibly fixed in the latest release), the workflow will automatically close the issue in 14 days. Thank you for your contributions.

[aauren]

Still relevant

[github-actions]

This repository uses an automated workflow to automatically label issues which have not had any activity (commit/comment/label) for 60 days. This helps us manage the community issues better. If the issue is still relevant, please add a comment to the issue so the workflow can remove the label and we know it is still valid. If it is no longer relevant (or possibly fixed in the latest release), the workflow will automatically close the issue in 14 days. Thank you for your contributions.

[zmedico]

After experiencing rancher/rancher#43356 with rancher 2.8.2 (maybe fixed by #3536), I've come to appreciate the stability of etcd scaling with rancher 2.7.x releases, even without support for the etcd learner role.