🌱 Add Node watch to Machine controller

[sedefsavas]

What this PR does / why we need it:
Forward porting #3748

[fabriziopandini]

/lgtm

[ncdc]

I didn't catch this in the 0.3 PR, but I just noticed that we're not restricting to machines in a specific namespace or for a specific cluster. We should probably do that, to avoid any possible false positives (e.g. 2 clusters in 2 different VPCs that have the same node name for a node).

func (r *MachineReconciler) nodeToMachine(namespace, clusterName string) func(o client.Object) []reconcile.Request {
  return func(o client.Object) []reconcile.Request {
    // use namespace and clusterName in r.Client.List
  }
}

WDYT? cc @vincepri @fabriziopandini

[vincepri]

This makes sense, it helps with potential conflicts, although it needs to be tested if we can mix and match field matchers with normal ones

[ncdc]

You mean InNamespace + MatchingFields? Any reason to think that wouldn't work?

[ncdc]

Looking at the CacheReader implementation, it looks like:

1. If there is a field selector, respect that
2. Else, if there is a namespace match, use that
3. Else, list everything

THEN, if there is a label selector, honor that.

So we can't do namespace + field selector 😦

[ncdc]

Maybe we should enhance this in C-R?

[ncdc]

See https://github.com/kubernetes-sigs/controller-runtime/blob/5c2b42d0dfe264fe1a187dcb11f384c0d193c042/pkg/cache/internal/cache_reader.go#L97-L112

and then

https://github.com/kubernetes-sigs/controller-runtime/blob/5c2b42d0dfe264fe1a187dcb11f384c0d193c042/pkg/cache/internal/cache_reader.go#L133-L134

[vincepri]

Yes, this seems like it could be a good improvement there

[vincepri]

Do we want to file an issue and merge this PR as-is for now given that's just forward porting?

[ncdc]

Yes

[vincepri]

/milestone v0.4.0

[vincepri]

/approve

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