Can't seem to reproduce

This problem really exists for the following version:

appdelivery@appdelivery-qvm-1:~$ minikube version
minikube version: v1.12.1
commit: 997fd89b9d3a0072e3112c79d906b6367e760473-dirty

@BlackCrowned it is right when you first run the minikube start command, and when you re-run the minikube start, it is wrong. So if you just run a new minikube, you will not reproduce it.

@BlackCrowned I found the code which cause this error:

https://github.com/kubernetes/minikube/blob/master/cmd/minikube/cmd/start_flags.go#L539

viper.GetStringSlice does not return the expected slice.

I0813 14:45:12.401533   90740 start_flags.go:539] existing: {v1.18.3 minikube minikubeCA [k8s-beta.duokexuetang.com k8s-prod-replica.duokexuetang.com] [] cluster.local docker    10.96.0.0/12    [] true false   8443 }
I0813 14:45:12.401574   90740 start_flags.go:540] viper: [[k8s-beta.duokexuetang.com,k8s-prod-replica.duokexuetang.com]]

It is a bug caused by package viper

// ToStringSliceE casts an interface to a []string type.
func ToStringSliceE(i interface{}) ([]string, error) {
	var a []string

	switch v := i.(type) {
	case []interface{}:
		for _, u := range v {
			a = append(a, ToString(u))
		}
		return a, nil
	case []string:
		return v, nil
	case string:
		return strings.Fields(v), nil
	case interface{}:
		str, err := ToStringE(v)
		if err != nil {
			return a, fmt.Errorf("unable to cast %#v of type %T to []string", i, i)
		}
		return []string{str}, nil
	default:
		return a, fmt.Errorf("unable to cast %#v of type %T to []string", i, i)
	}
}

@BlackCrowned I write a simple program to express what happens.

package main

import (
	"encoding/json"
	"fmt"
	"github.com/spf13/cobra"
	"github.com/spf13/viper"
)

var apiserverNames []string

type ClusterConfig struct {
	KubernetesConfig KubernetesConfig
}

type KubernetesConfig struct {
	APIServerNames []string
}

var startCmd = cobra.Command{
	Use: "start",
	Run: func(cmd *cobra.Command, args []string) {
		fmt.Println("apiserverNames=", viper.GetStringSlice("apiserver-names"))
		kubeConfig := KubernetesConfig{
			APIServerNames: apiserverNames,
		}
		clusterConfig := ClusterConfig{
			KubernetesConfig: kubeConfig,
		}
		data, _ := json.MarshalIndent(&clusterConfig, "", "    ")
		fmt.Println("Output=", string(data))
	},
}

func init() {
	startCmd.PersistentFlags().StringArrayVar(&apiserverNames, "apiserver-names", nil, "apiserver names")
	viper.BindPFlags(startCmd.PersistentFlags())
}

func main() {
	rootCmd := cobra.Command{}
	rootCmd.AddCommand(&startCmd)
	fmt.Println(rootCmd.Execute())
}

Output:

apiserverNames= [[hello,world]]
Output= {
    "KubernetesConfig": {
        "APIServerNames": [
            "hello",
            "world"
        ]
    }
}

@jemygraw Thank you for looking into this and creating a new issue!