add --dry-run flag to kubectl apply

Related StackOverflow:
http://stackoverflow.com/questions/38824409/validate-openshift-objects-defined-in-yaml-before-actually-applying-or-executing

This patch adds a `--dry-run` flag to the `apply` command in order to
allow validation of objects, without actually creating them. If a
`--dry-run` flag is present and no validation errors are found, the
command will exit before patching or creating any objects.

It also adds a `--dry-run` option to the `kubectl create` root command.

pkg/kubectl/cmd/apply.go

@@ -101,7 +101,8 @@ func NewCmdApply(f *cmdutil.Factory, out io.Writer) *cobra.Command {
 	cmdutil.AddValidateFlags(cmd)
 	cmd.Flags().StringVarP(&options.Selector, "selector", "l", "", "Selector (label query) to filter on")
 	cmd.Flags().Bool("all", false, "[-all] to select all the specified resources.")
-	cmdutil.AddOutputFlagsForMutation(cmd)
+	cmdutil.AddDryRunFlag(cmd)
+	cmdutil.AddPrinterFlags(cmd)
 	cmdutil.AddRecordFlag(cmd)
 	cmdutil.AddInclude3rdPartyFlags(cmd)
 	return cmd
@@ -148,6 +149,8 @@ func RunApply(f *cmdutil.Factory, cmd *cobra.Command, out io.Writer, options *Ap
 		return err
 	}
 
+	dryRun := cmdutil.GetFlagBool(cmd, "dry-run")
+
 	encoder := f.JSONEncoder()
 	decoder := f.Decoder(false)
 
@@ -195,6 +198,7 @@ func RunApply(f *cmdutil.Factory, cmd *cobra.Command, out io.Writer, options *Ap
 				}
 			}
 
+			if !dryRun {
 				// Then create the resource and skip the three-way merge
 				if err := createAndRefresh(info); err != nil {
 					return cmdutil.AddSourceToErr("creating", info.Source, err)
@@ -204,11 +208,14 @@ func RunApply(f *cmdutil.Factory, cmd *cobra.Command, out io.Writer, options *Ap
 				} else {
 					visitedUids.Insert(string(uid))
 				}
+			}
+
 			count++
-			cmdutil.PrintSuccess(mapper, shortOutput, out, info.Mapping.Resource, info.Name, false, "created")
+			cmdutil.PrintSuccess(mapper, shortOutput, out, info.Mapping.Resource, info.Name, dryRun, "created")
 			return nil
 		}
 
+		if !dryRun {
 			overwrite := cmdutil.GetFlagBool(cmd, "overwrite")
 			helper := resource.NewHelper(info.Client, info.Mapping)
 			patcher := NewPatcher(encoder, decoder, info.Mapping, helper, overwrite)
@@ -234,8 +241,9 @@ func RunApply(f *cmdutil.Factory, cmd *cobra.Command, out io.Writer, options *Ap
 			} else {
 				visitedUids.Insert(string(uid))
 			}
+		}
 		count++
-		cmdutil.PrintSuccess(mapper, shortOutput, out, info.Mapping.Resource, info.Name, false, "configured")
+		cmdutil.PrintSuccess(mapper, shortOutput, out, info.Mapping.Resource, info.Name, dryRun, "configured")
 		return nil
 	})
 

pkg/kubectl/cmd/create.go

@@ -66,9 +66,10 @@ func NewCmdCreate(f *cmdutil.Factory, out io.Writer) *cobra.Command {
 	cmdutil.AddFilenameOptionFlags(cmd, options, usage)
 	cmd.MarkFlagRequired("filename")
 	cmdutil.AddValidateFlags(cmd)
-	cmdutil.AddOutputFlagsForMutation(cmd)
+	cmdutil.AddPrinterFlags(cmd)
 	cmdutil.AddApplyAnnotationFlags(cmd)
 	cmdutil.AddRecordFlag(cmd)
+	cmdutil.AddDryRunFlag(cmd)
 	cmdutil.AddInclude3rdPartyFlags(cmd)
 
 	// create subcommands
@@ -116,6 +117,8 @@ func RunCreate(f *cmdutil.Factory, cmd *cobra.Command, out io.Writer, options *r
 		return err
 	}
 
+	dryRun := cmdutil.GetFlagBool(cmd, "dry-run")
+
 	count := 0
 	err = r.Visit(func(info *resource.Info, err error) error {
 		if err != nil {
@@ -131,16 +134,19 @@ func RunCreate(f *cmdutil.Factory, cmd *cobra.Command, out io.Writer, options *r
 			}
 		}
 
+		if !dryRun {
 			if err := createAndRefresh(info); err != nil {
 				return cmdutil.AddSourceToErr("creating", info.Source, err)
 			}
+		}
 
 		count++
 		shortOutput := cmdutil.GetFlagString(cmd, "output") == "name"
 		if !shortOutput {
 			f.PrintObjectSpecificMessage(info.Object, out)
 		}
-		cmdutil.PrintSuccess(mapper, shortOutput, out, info.Mapping.Resource, info.Name, false, "created")
+
+		cmdutil.PrintSuccess(mapper, shortOutput, out, info.Mapping.Resource, info.Name, dryRun, "created")
 		return nil
 	})
 	if err != nil {