GoLang 12factor config with viper

config.go

package config

import (
	"github.com/spf13/viper"
	"sync"
)

var instance *Config
var once sync.Once

func Of() *Config {
	once.Do(func() {
		Load()
	})
	return instance
}

func Load() {
	vp := viper.New()
	// follow 12 factors principles https://www.12factor.net/config
	vp.AutomaticEnv()
	// just for development environment
	vp.SetConfigName("development.env")
	vp.SetConfigType("env")
	vp.AddConfigPath(".")
	vp.ReadInConfig()
	vp.Unmarshal(&instance)
}

// Mock this method is used to mock the config
// only for testing purpose
func Mock(v *viper.Viper) {
	v.Unmarshal(&instance)
}

type Config struct {
  Port string     `env:"PORT"`
  Nest NestConfig `env:"NestConfig"`
}

type NestConfig struct {
  MarsenNo   int  `env:"MarsenNo"`
  MarsenFlag bool `env:"MarsenFlag"`
}