docker/swarmkit

package node

import (
    "fmt"

    "github.com/moby/swarmkit/v2/api"
    "github.com/spf13/cobra"
)

var (
    promoteCmd = &cobra.Command{
        Use:   "promote <node ID>",
        Short: "Promote a node to a manager",
        RunE: func(cmd *cobra.Command, args []string) error {
            if err := changeNodeRole(cmd, args, api.NodeRoleManager); err != nil {
                if err == errNoChange {
                    return fmt.Errorf("Node %s is already a manager", args[0])
                }
                return err
            }
            return nil
        },
    }
)