Merge pull request kubernetes#44606 from ivan4th/fix-serialization-of…

…-enforce-node-allocatable

Automatic merge from submit-queue (batch tested with PRs 44606, 46038)

Fix serialization of EnforceNodeAllocatable

EnforceNodeAllocatable being `nil` and `[]` are treated in different
ways by kubelet. Namely, `nil` is replaced with `[]string{"pods"}` by
the defaulting mechanism.

E.g. if you run kubelet in Docker-in-Docker environment
you may need to run it with the following options:
`--cgroups-per-qos=false --enforce-node-allocatable=`
(this corresponds to EnforceNodeAllocatable being empty array and not
null) If you then grab kubelet configuration via /configz and try to
reuse it for dynamic kubelet config, kubelet will think that
EnforceNodeAllocatable is null, failing to run in the
Docker-in-Docker environment.

Encountered this while updating Virtlet for Kubernetes 1.6
(the dev environment is based on kubeadm-dind-cluster)

pkg/apis/componentconfig/v1alpha1/types.go

@@ -605,7 +605,7 @@ type KubeletConfiguration struct {
 	// This flag specifies the various Node Allocatable enforcements that Kubelet needs to perform.
 	// This flag accepts a list of options. Acceptible options are `pods`, `system-reserved` & `kube-reserved`.
 	// Refer to [Node Allocatable](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/node-allocatable.md) doc for more information.
-	EnforceNodeAllocatable []string `json:"enforceNodeAllocatable,omitempty"`
+	EnforceNodeAllocatable []string `json:"enforceNodeAllocatable"`
 	// This flag, if set, will avoid including `EvictionHard` limits while computing Node Allocatable.
 	// Refer to [Node Allocatable](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/node-allocatable.md) doc for more information.
 	ExperimentalNodeAllocatableIgnoreEvictionThreshold bool `json:"experimentalNodeAllocatableIgnoreEvictionThreshold,omitempty"`

pkg/apis/componentconfig/v1alpha1/zz_generated.conversion.go

@@ -729,7 +729,11 @@ func autoConvert_componentconfig_KubeletConfiguration_To_v1alpha1_KubeletConfigu
 	out.KubeReserved = *(*map[string]string)(unsafe.Pointer(&in.KubeReserved))
 	out.SystemReservedCgroup = in.SystemReservedCgroup
 	out.KubeReservedCgroup = in.KubeReservedCgroup
-	out.EnforceNodeAllocatable = *(*[]string)(unsafe.Pointer(&in.EnforceNodeAllocatable))
+	if in.EnforceNodeAllocatable == nil {
+		out.EnforceNodeAllocatable = make([]string, 0)
+	} else {
+		out.EnforceNodeAllocatable = *(*[]string)(unsafe.Pointer(&in.EnforceNodeAllocatable))
+	}
 	out.ExperimentalNodeAllocatableIgnoreEvictionThreshold = in.ExperimentalNodeAllocatableIgnoreEvictionThreshold
 	return nil
 }