RFE: use learner mode for joining etcd members

[fabriziopandini]

Growing a local etcd cluster is a complex operation, and in the past, we already faced some issues like e.g. #588

Now that the implementation of the etcd learner mode is progressing, we should start considering if to use it in kubeadm in order to make join --control-plane implementation more robust.

at a high level what we would like to achieve is:

• a new etcd member should be created as a learner and became a voting member only after the etcd data are fully aligned.
  ideally
• we should also prevent the api-server to read from a learner node

Ref docs:

• https://etcd.io/docs/v3.3.12/learning/learner/
• https://etcd.io/docs/v3.4.0/learning/design-learner/

[fabriziopandini]

/close
wrong repo 🤣

[k8s-ci-robot]

@fabriziopandini: Closing this issue.

In response to this:

/close
wrong repo 🤣

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