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Ignore daemonset-controller-hash label key in federation before comparing the federated object with its cluster equivalent.

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Kubernetes daemonset controller writes a daemonset's hash to the object
label as an optimization to avoid recomputing it every time. Adding a
new label to the object that the federation is unaware of causes
problems because federated controllers compare the objects in
federation and their equivalents in clusters and try to reconcile them.
This leads to a constant fight between the federated daemonset
controller and the cluster controllers, and they never reach a stable
state.

Ideally, cluster components should not update an object's spec or
metadata in a way federation cannot replicate. They can update an
object's status though. Therefore, this daemonset hash should be a
field in daemonset's status, not a label in object meta. @janetkuo says
that this label is only a short term solution. In the near future, they
are going to replace it with revision numbers in daemonset status. We
can then rip this bandaid out.
This commit is contained in:
Madhusudan.C.S 2017-06-06 21:27:31 -07:00
parent f33a5f8bff
commit 3530c9ce87
1 changed files with 25 additions and 0 deletions
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25
federation/pkg/federatedtypes/daemonset.go
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@ -72,6 +72,31 @@ func (a *DaemonSetAdapter) Copy(obj pkgruntime.Object) pkgruntime.Object {
func (a *DaemonSetAdapter) Equivalent(obj1, obj2 pkgruntime.Object) bool {
daemonset1 := obj1.(*extensionsv1.DaemonSet)
daemonset2 := obj2.(*extensionsv1.DaemonSet)
// Kubernetes daemonset controller writes a daemonset's hash to
// the object label as an optimization to avoid recomputing it every
// time. Adding a new label to the object that the federation is
// unaware of causes problems because federated controllers compare
// the objects in federation and their equivalents in clusters and
// try to reconcile them. This leads to a constant fight between the
// federated daemonset controller and the cluster controllers, and
// they never reach a stable state.
//
// Ideally, cluster components should not update an object's spec or
// metadata in a way federation cannot replicate. They can update an
// object's status though. Therefore, this daemonset hash should
// be a field in daemonset's status, not a label in object meta.
// @janetkuo says that this label is only a short term solution. In
// the near future, they are going to replace it with revision numbers
// in daemonset status. We can then rip this bandaid out.
//
// We are deleting the keys here and that should be fine since we are
// working on object copies. Also, propagating the deleted labels
// should also be fine because we don't support daemonset rolling
// update in federation yet.
delete(daemonset1.ObjectMeta.Labels, extensionsv1.DefaultDaemonSetUniqueLabelKey)
delete(daemonset2.ObjectMeta.Labels, extensionsv1.DefaultDaemonSetUniqueLabelKey)
return util.ObjectMetaEquivalent(daemonset1.ObjectMeta, daemonset2.ObjectMeta) && reflect.DeepEqual(daemonset1.Spec, daemonset2.Spec)
}