feat(scale): basic service scale command

cmd/uncloud/service/root.go

@@ -14,6 +14,7 @@ func NewRootCommand() *cobra.Command {
 		NewListCommand(),
 		NewRmCommand(),
 		NewRunCommand(),
+		NewScaleCommand(),
 	)
 	return cmd
 }

cmd/uncloud/service/scale.go

@@ -0,0 +1,161 @@
+package service
+
+import (
+	"context"
+	"fmt"
+	"github.com/charmbracelet/huh"
+	"github.com/docker/compose/v2/pkg/progress"
+	"github.com/spf13/cobra"
+	"strconv"
+	"uncloud/internal/api"
+	"uncloud/internal/cli"
+)
+
+type scaleOptions struct {
+	service  string
+	replicas uint
+	cluster  string
+}
+
+func NewScaleCommand() *cobra.Command {
+	opts := scaleOptions{}
+	cmd := &cobra.Command{
+		Use:   "scale SERVICE REPLICAS",
+		Short: "Scale a replicated service by changing the number of replicas.",
+		Long:  "Scale a replicated service by changing the number of replicas. Scaling down requires confirmation.",
+		Args:  cobra.ExactArgs(2),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			uncli := cmd.Context().Value("cli").(*cli.CLI)
+
+			opts.service = args[0]
+			replicas, err := strconv.ParseUint(args[1], 10, 0)
+			if err != nil {
+				return fmt.Errorf("invalid number of replicas: %w", err)
+			}
+			opts.replicas = uint(replicas)
+
+			return scale(cmd.Context(), uncli, opts)
+		},
+	}
+
+	cmd.Flags().StringVarP(
+		&opts.cluster, "cluster", "c", "",
+		"Name of the cluster. (default is the current cluster)",
+	)
+
+	return cmd
+}
+
+func scale(ctx context.Context, uncli *cli.CLI, opts scaleOptions) error {
+	if opts.replicas == 0 {
+		return fmt.Errorf(
+			"scaling to zero replicas is not supported. This would effectively remove the service without preserving "+
+				"its configuration, making it impossible to scale back up. Uncloud derives the service configuration "+
+				"from existing containers. Use 'uc rm %s' instead if you want to remove the service",
+			opts.service,
+		)
+	}
+
+	clusterClient, err := uncli.ConnectCluster(ctx, opts.cluster)
+	if err != nil {
+		return fmt.Errorf("connect to cluster: %w", err)
+	}
+	defer clusterClient.Close()
+
+	svc, err := clusterClient.InspectService(ctx, opts.service)
+	if err != nil {
+		return fmt.Errorf("inspect service '%s': %w", opts.service, err)
+	}
+
+	if svc.Mode != api.ServiceModeReplicated {
+		return fmt.Errorf("scaling is only supported for services in %s mode, service '%s' is in %s mode",
+			api.ServiceModeReplicated, svc.Name, svc.Mode)
+	}
+
+	currentReplicas := uint(len(svc.Containers))
+
+	if currentReplicas == opts.replicas {
+		fmt.Printf("Service '%s' already has %d replicas. No changes required.\n", svc.Name, currentReplicas)
+		return nil
+	}
+
+	// TODO: Check if all containers have the same spec. If not, prompt user to choose which one to scale.
+	//  This can happen if a service deployment failed midway and some containers were not updated.
+	// Derive the service spec from the first container.
+	spec, err := svc.Containers[0].Container.ServiceSpec()
+	if err != nil {
+		return fmt.Errorf("get service spec from container: %w", err)
+	}
+
+	spec.Replicas = opts.replicas
+
+	deploy, err := clusterClient.NewDeployment(spec, nil)
+	if err != nil {
+		return fmt.Errorf("create deployment: %w", err)
+	}
+
+	plan, err := deploy.Plan(ctx)
+	if err != nil {
+		return fmt.Errorf("plan deployment: %w", err)
+	}
+
+	if len(plan.Operations) == 0 {
+		fmt.Printf("Service '%s' is already scaled to %d replicas.\n", svc.Name, opts.replicas)
+		return nil
+	}
+
+	if opts.replicas < currentReplicas {
+		// Initialise a machine and container name resolver to properly format the plan output.
+		resolver, err := clusterClient.ServiceOperationNameResolver(ctx, svc)
+		if err != nil {
+			return fmt.Errorf("create machine and container name resolver for service operations: %w", err)
+		}
+
+		fmt.Printf("Scaling plan for service %s (%d → %d replicas):\n", svc.Name, currentReplicas, opts.replicas)
+		fmt.Println(plan.Format(resolver))
+		fmt.Println()
+
+		// Ask for confirmation before scaling down as it may cause data loss.
+		confirmed, err := confirm()
+		if err != nil {
+			return fmt.Errorf("confirm scaling: %w", err)
+		}
+		if !confirmed {
+			fmt.Println("Cancelled. No changes were made.")
+			return nil
+		}
+	}
+
+	title := fmt.Sprintf("Scaling service %s (%d → %d replicas)", svc.Name, currentReplicas, opts.replicas)
+	err = progress.RunWithTitle(ctx, func(ctx context.Context) error {
+		if _, err = deploy.Run(ctx); err != nil {
+			return fmt.Errorf("deploy service: %w", err)
+		}
+		return nil
+	}, uncli.ProgressOut(), title)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func confirm() (bool, error) {
+	var confirmed bool
+	form := huh.NewForm(
+		huh.NewGroup(
+			huh.NewConfirm().
+				Title(
+					"Do you want to continue?",
+				).
+				Affirmative("Yes!").
+				Negative("No").
+				Value(&confirmed),
+		),
+	)
+	if err := form.Run(); err != nil {
+		return false, err
+	}
+
+	return confirmed, nil
+}