Allow admin user to explicitly unschedule the node

Setting Unschedulable on the node will not touch any existing pods
on the node but will block scheduling of new pods on the node.

pkg/api/types.go

@@ -782,13 +782,18 @@ type EndpointsList struct {
 
 // NodeSpec describes the attributes that a node is created with.
 type NodeSpec struct {
-	// Capacity represents the available resources of a node
+	// Capacity represents the available resources of a node.
 	Capacity ResourceList `json:"capacity,omitempty"`
+
 	// PodCIDR represents the pod IP range assigned to the node
 	// Note: assigning IP ranges to nodes might need to be revisited when we support migratable IPs.
 	PodCIDR string `json:"podCIDR,omitempty"`
+
 	// External ID of the node assigned by some machine database (e.g. a cloud provider)
 	ExternalID string `json:"externalID,omitempty"`
+
+	// Unschedulable controls node schedulability of new pods. By default node is schedulable.
+	Unschedulable bool `json:"unschedulable,omitempty"`
 }
 
 // NodeSystemInfo is a set of ids/uuids to uniquely identify the node.
@@ -842,6 +847,8 @@ const (
 	NodeReachable NodeConditionType = "Reachable"
 	// NodeReady means the node returns StatusOK for HTTP health check.
 	NodeReady NodeConditionType = "Ready"
+	// NodeSchedulable means the node is ready to accept new pods.
+	NodeSchedulable NodeConditionType = "Schedulable"
 )
 
 type NodeCondition struct {