InstallConfig machine pool typing and validation

[wking]

Spun off from this thread, @dgoodwin expressed concerns about Machines corner cases. What if no pool named master is configured? What if multiple pools named master is configured? What if a pool named somethingTheInstallerDoesNotUnderstand is configured? I'd floated:

Master MachinePool `json:"master"

Worker MachinePool `json:"worker"

but @dgoodwin pointed out compat issues between that approach and ClusterDeployment information.

@abhinavdahiya suggested we leave Machines alone, but we don't currently have any validation for Machines, and I expect we'll want to have some at some point.

@dgoodwin suggested leaving Machines as it stands but adding a typed variable for the name with constants for the master and worker names (he suggested control-plane and compute for the names) with verification checking for exactly one control-plane and at least one compute. He didn't give an opinion on the somethingTheInstallerDoesNotUnderstand case.

I'm not clear enough on the trade-offs to have much of an opinion here, but think we should sort out how we want verification to work here before InstallConfig gets too popular and migration becomes difficult ;).

[dgoodwin]

One thing I didn't think of at the time was:

ControlPlane MachinePool
Compute MachinePool[]

I would be ok with this as it's flexible enough for the long term definition of what should exist in the cluster. You could enforce compute only contains one at install time if you wanted.

I'd suggest avoiding "Master" and going "ControlPlane" as that's been a consistent trend as far as I can tell lately.

But yes if leaving as is I think explicit type identifiers would be better than assumptions about names, and let the user choose the names.

[wking]

@abhinavdahiya, what do you think about:

ControlPlane MachinePool
Compute MachinePool[]

?

[crawford]

Closing due to inactivity.

[openshift-ci-robot]

@crawford: Closing this issue.

In response to this:

Closing due to inactivity.

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[wking]

I'm still in favor of this change, but was waiting for feedback from other maintainers ;). Mind if I just go ahead and work up a PR?

[dgoodwin]

I think @abutcher has one in flight for #264