Add node labelling

[liger1978]

Fixes #509

[ckotzbauer]

Hi @liger1978,
thanks for your PR and working on the issue. This is much appreciated!

Some thoughts to the label-feature:

• The labels are only added, never removed. The zalando-usecase is toggling the node-label-value. Would it be better to remove the before-labels when the after-labels are applied? I think this is more in line with user expectations.
• I'm not sure about the cli-flag-names. What about pre-reboot-node-labels and post-reboot-node-labels?

Can you please separate the spelling corrections and readme updates from this PR? It's hard to review, when there are many other changes which aren't directly related to a PR. Please always open separate PRs for that.

Thanks!

/cc @evrardjp @jackfrancis Thoughts?

[liger1978]

@ckotzbauer I'm not sure what "removing a label" means in this context. In ready state, nodes will already have a label like zalando with a value like ready. Before reboot this must be set to something else, like notready (causing the operator to move the database leader role to a pod on another node). After reboot the label will be set back to ready. I've tested this and it works with the Zalando feature. I'm not sure where you are suggesting a label should be removed in this workflow.

[liger1978]

@ckotzbauer I've updated the PR with the other requested changes.

[ckotzbauer]

Thanks for your changes.
What you want (and the zalando-usecase is) is, that you toggle values of the same node-label. However the implementation only adds two sets of labels.
From the wording, I'm not sure if all our users understand that this feature is only really useful if you add pre- and post-labels for the same label-keys.
There are no enforcements that all label-keys from pre-reboot-node-labels are also configured as post-reboot-node-labels. If this is something a component in the cluster (e.g. monitoring) expects, than the reboot is done and the label is still present and indicates a reboot.

[liger1978]

@ckotzbauer OK, so what would you prefer? Please can you be specific in the behaviour you require as I am struggling to understand what you want (my limitation no doubt).

[ckotzbauer]

I think the simplest thing would be a validation, that all label-keys set as pre-reboot-label are also set as post-reboot-labels and vice versa. This should also be described at the README.

[liger1978]

@ckotzbauer I've added the verification and updated the readme as requested.

[liger1978]

@jackfrancis I have implemented your suggestions.

[ckotzbauer]

From my perspective this looks good now. @jackfrancis do you want to have a final look?
I would include this into 1.10.0 if there are not objections.

[jackfrancis]

lgtm

[liger1978]

Thanks. Please can it be merged!

[erwbgy]

@liger1978 One minor niggle. The current implementation has pre-reboot-node-labels and after-reboot-node-labels, which I find confusing. IMO the latter should be post-reboot-node-labels as per the original suggestion from @ckotzbauer.

Or alternatively before-reboot-node-labels and after-reboot-node-labels.

[ckotzbauer]

Yes, you are right @erwbgy. Thanks for the hint. This should be fixed.

[liger1978]

@erwbgy @ckotzbauer @jackfrancis I have made this change. Please review/approve/merge. Thank you!

[liger1978]

@ckotzbauer Thank you very much for merging! Do you have any idea when we can expect a new release with these changes included?

[ckotzbauer]

I think in the next week.