cvo: separate option validation and cvo execution

Extract option validation to a new `ValidateAndComplete()` method, and run it separate from `Run()` through cobra `PreRunE`

Author: petr-muller

cmd/cluster-version-operator/start.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+
 	"github.com/spf13/cobra"
 	"k8s.io/klog/v2"
 
@@ -15,10 +16,12 @@ func init() {
 		Use:   "start",
 		Short: "Starts Cluster Version Operator",
 		Long:  "",
-		Run: func(cmd *cobra.Command, args []string) {
+		PreRunE: func(_ *cobra.Command, _ []string) error {
 			// To help debugging, immediately log version
 			klog.Info(version.String)
-
+			return opts.ValidateAndComplete()
+		},
+		Run: func(_ *cobra.Command, _ []string) {
 			if err := opts.Run(context.Background()); err != nil {
 				klog.Fatalf("error: %v", err)
 			}

pkg/start/start.go

@@ -132,7 +132,7 @@ func NewOptions() *Options {
 	}
 }
 
-func (o *Options) Run(ctx context.Context) error {
+func (o *Options) ValidateAndComplete() error {
 	if o.NodeName == "" {
 		return fmt.Errorf("node-name is required")
 	}
@@ -152,6 +152,20 @@ func (o *Options) Run(ctx context.Context) error {
 		(o.PromQLTarget.KubeSvc.Namespace == "" || o.PromQLTarget.KubeSvc.Name == "") {
 		return fmt.Errorf("--use-dns-for-services is disabled, so --metrics-service and --metrics-namespace must be set")
 	}
+
+	if parsed, err := url.Parse(o.PrometheusURLString); err != nil {
+		return fmt.Errorf("error parsing promql url: %v", err)
+	} else {
+		o.PromQLTarget.URL = parsed
+	}
+
+	// Inject the cluster ID into PromQL queries in HyperShift
+	o.InjectClusterIdIntoPromQL = o.HyperShift
+
+	return nil
+}
+
+func (o *Options) Run(ctx context.Context) error {
 	if len(o.PayloadOverride) > 0 {
 		klog.Warningf("Using an override payload directory for testing only: %s", o.PayloadOverride)
 	}
@@ -163,16 +177,6 @@ func (o *Options) Run(ctx context.Context) error {
 		return fmt.Errorf("--always-enable-capabilities was set with unknown capabilities: %v", unknownCaps)
 	}
 
-	// Inject the cluster ID into PromQL queries in HyperShift
-	o.InjectClusterIdIntoPromQL = o.HyperShift
-
-	// parse the prometheus url
-	var err error
-	o.PromQLTarget.URL, err = url.Parse(o.PrometheusURLString)
-	if err != nil {
-		return fmt.Errorf("error parsing promql url: %v", err)
-	}
-
 	// initialize the core objects
 	cb, err := newClientBuilder(o.Kubeconfig)
 	if err != nil {