Add new --wait-for-creation flag in kubectl wait command

kubectl wait command errors out when the waited resource does not exist.
But we need to provide a way to the users about intentionally also waiting for
the creation of resources.

This PR introduces a new flag to cover waiting for the creation of resources
with preserving the default behavior.

Kubernetes-commit: e24b9a022f3b1e97ea538c9754d4d38f119f275e

pkg/cmd/wait/wait.go

@@ -82,7 +82,10 @@ var (
 
 		# Wait for the pod "busybox1" to be deleted, with a timeout of 60s, after having issued the "delete" command
 		kubectl delete pod/busybox1
-		kubectl wait --for=delete pod/busybox1 --timeout=60s`))
+		kubectl wait --for=delete pod/busybox1 --timeout=60s
+
+		# Wait for the creation of the service "loadbalancer" in addition to wait to have ingress
+		kubectl wait --for=jsonpath='{.status.loadBalancer.ingress}' service/loadbalancer --wait-for-creation`))
 )
 
 // errNoMatchingResources is returned when there is no resources matching a query.
@@ -96,8 +99,9 @@ type WaitFlags struct {
 	PrintFlags           *genericclioptions.PrintFlags
 	ResourceBuilderFlags *genericclioptions.ResourceBuilderFlags
 
-	Timeout      time.Duration
-	ForCondition string
+	Timeout         time.Duration
+	ForCondition    string
+	WaitForCreation bool
 
 	genericiooptions.IOStreams
 }
@@ -115,7 +119,8 @@ func NewWaitFlags(restClientGetter genericclioptions.RESTClientGetter, streams g
 			WithLocal(false).
 			WithLatest(),
 
-		Timeout: 30 * time.Second,
+		Timeout:         30 * time.Second,
+		WaitForCreation: true,
 
 		IOStreams: streams,
 	}
@@ -152,6 +157,7 @@ func (flags *WaitFlags) AddFlags(cmd *cobra.Command) {
 
 	cmd.Flags().DurationVar(&flags.Timeout, "timeout", flags.Timeout, "The length of time to wait before giving up.  Zero means check once and don't wait, negative means wait for a week.")
 	cmd.Flags().StringVar(&flags.ForCondition, "for", flags.ForCondition, "The condition to wait on: [delete|condition=condition-name[=condition-value]|jsonpath='{JSONPath expression}'=[JSONPath value]]. The default condition-value is true.  Condition values are compared after Unicode simple case folding, which is a more general form of case-insensitivity.")
+	cmd.Flags().BoolVar(&flags.WaitForCreation, "wait-for-creation", flags.WaitForCreation, "The default value is true. If set to true, also wait for creation of objects if they do not already exist. This flag is ignored in --for=delete")
 }
 
 // ToOptions converts from CLI inputs to runtime inputs
@@ -180,10 +186,11 @@ func (flags *WaitFlags) ToOptions(args []string) (*WaitOptions, error) {
 	}
 
 	o := &WaitOptions{
-		ResourceFinder: builder,
-		DynamicClient:  dynamicClient,
-		Timeout:        effectiveTimeout,
-		ForCondition:   flags.ForCondition,
+		ResourceFinder:  builder,
+		DynamicClient:   dynamicClient,
+		Timeout:         effectiveTimeout,
+		ForCondition:    flags.ForCondition,
+		WaitForCreation: flags.WaitForCreation,
 
 		Printer:     printer,
 		ConditionFn: conditionFn,
@@ -302,10 +309,11 @@ type WaitOptions struct {
 	ResourceFinder genericclioptions.ResourceFinder
 	// UIDMap maps a resource location to a UID.  It is optional, but ConditionFuncs may choose to use it to make the result
 	// more reliable.  For instance, delete can look for UID consistency during delegated calls.
-	UIDMap        UIDMap
-	DynamicClient dynamic.Interface
-	Timeout       time.Duration
-	ForCondition  string
+	UIDMap          UIDMap
+	DynamicClient   dynamic.Interface
+	Timeout         time.Duration
+	ForCondition    string
+	WaitForCreation bool
 
 	Printer     printers.ResourcePrinter
 	ConditionFn ConditionFunc
@@ -320,6 +328,40 @@ func (o *WaitOptions) RunWait() error {
 	ctx, cancel := watchtools.ContextWithOptionalTimeout(context.Background(), o.Timeout)
 	defer cancel()
 
+	isForDelete := strings.ToLower(o.ForCondition) == "delete"
+	if o.WaitForCreation && o.Timeout == 0 {
+		return fmt.Errorf("--wait-for-creation requires a timeout value greater than 0")
+	}
+
+	if o.WaitForCreation && !isForDelete {
+		err := func() error {
+			for {
+				select {
+				case <-ctx.Done():
+					return fmt.Errorf("context deadline is exceeded while waiting for the creation of the resources")
+				default:
+					err := o.ResourceFinder.Do().Visit(func(info *resource.Info, err error) error {
+						// We don't need to do anything after we assure that the resources exist. Because
+						// actual logic will be incorporated after we wait all the resources' existence.
+						return nil
+					})
+					// It is verified that all the resources exist.
+					if err == nil {
+						return nil
+					}
+					// We specifically wait for the creation of resources and all the errors
+					// other than not found means that this is something we cannot handle.
+					if !apierrors.IsNotFound(err) {
+						return err
+					}
+				}
+			}
+		}()
+		if err != nil {
+			return err
+		}
+	}
+
 	visitCount := 0
 	visitFunc := func(info *resource.Info, err error) error {
 		if err != nil {
@@ -338,7 +380,6 @@ func (o *WaitOptions) RunWait() error {
 		return err
 	}
 	visitor := o.ResourceFinder.Do()
-	isForDelete := strings.ToLower(o.ForCondition) == "delete"
 	if visitor, ok := visitor.(*resource.Result); ok && isForDelete {
 		visitor.IgnoreErrors(apierrors.IsNotFound)
 	}