Allow concurrent reconciliation only for distinct resources

[sebbonnet]

At present, reconcile.Reconciler allows multiple concurrent reconciliations through adjustment of the MaxConcurrentReconciles property to values above 1. However, this opens the possibility that there could be two concurrent reconciliations for the same resource, which is a situation we would like to avoid.

We would like to be able to configure the Reconciler so that it supports concurrent reconciliations only for distinct resources. In other words, it would be possible to concurrently reconcile resources A and B, but not to have two concurrent reconciliations for either A or B.

[DirectXMan12]

This shouldn't happen -- the underlying workqueue should prevent this from occurring (see the bullet item for "stingy" in https://godoc.org/k8s.io/client-go/util/workqueue). Do you see this actually occurring?

[DirectXMan12]

(if you do, it's a bug)

[sebbonnet]

That's a very good point - if it works as described it would simplify quite a few things on our end.
I'm currently testing this and will report here.

[sebbonnet]

@DirectXMan12 thanks for pointing that out!
You were right, the reconciler internal queue prevents concurrent updates for the same resource name, but still allows concurrent updates for different resources when MaxConcurrentReconciles is greater than 1.