Initial upgrade flow for control-plane

clitools/pkg/cmd/agent/agent.go

@@ -3,6 +3,8 @@ package agent
 import (
 	"context"
 	"fmt"
+	"os"
+	"path/filepath"
 	"time"
 
 	"github.com/spf13/cobra"
@@ -50,6 +52,11 @@ func NewCmdAgent(flags *genericclioptions.ConfigFlags) *cobra.Command {
 				return fmt.Errorf("node name is empty in rendered config")
 			}
 
+			ctx := cmd.Context()
+			if err := waitForControlGate(ctx, envFile, 2*time.Second); err != nil {
+				return fmt.Errorf("wait for control gate to release: %w", err)
+			}
+
 			klog.InfoS("starting agent",
 				"node", cfg.Spec.NodeName,
 				"namespace", namespace,
@@ -62,7 +69,6 @@ func NewCmdAgent(flags *genericclioptions.ConfigFlags) *cobra.Command {
 				return fmt.Errorf("create kube clients: %w", err)
 			}
 
-			ctx := cmd.Context()
 			return runPollLoop(ctx, clients, namespace, cfg.Spec.NodeName, pollInterval)
 		},
 	}
@@ -74,6 +80,36 @@ func NewCmdAgent(flags *genericclioptions.ConfigFlags) *cobra.Command {
 	return cmd
 }
 
+func waitForControlGate(ctx context.Context, envFile string, pollInterval time.Duration) error {
+	dir := filepath.Dir(envFile)
+	marker := filepath.Join(dir, ".control-gate")
+
+	if pollInterval <= 0 {
+		pollInterval = 2 * time.Second
+	}
+
+	ticker := time.NewTicker(pollInterval)
+	defer ticker.Stop()
+
+	for {
+		_, err := os.Stat(marker)
+		if err == nil {
+			klog.InfoS("Control gate is present; waiting before starting poll loop", "path", marker)
+		} else if os.IsNotExist(err) {
+			klog.InfoS("Control gate not present; starting poll loop", "path", marker)
+			return nil
+		} else {
+			return fmt.Errorf("stat upgrade marker %s: %w", marker, err)
+		}
+
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-ticker.C:
+		}
+	}
+}
+
 func runPollLoop(ctx context.Context, clients *kube.Clients, namespace, nodeName string, interval time.Duration) error {
 	gvr := schema.GroupVersionResource{
 		Group:    monov1alpha1.Group,