config.go

package configReloader

import (
	"encoding/json"

	"fmt"
	"io/ioutil"
	"os"
	"os/signal"
	"syscall"
)

// ApplicationConfig struct represents the configuration for the program
type ApplicationConfig struct {
	Config       ServerConfig            `json:"config"`
	Ppids        map[string]*RouteConfig `json:"ppids"`
	IPRanges     map[string]*RouteConfig `json:"ip_ranges"`
	Applications map[string]*RouteConfig `json:"applications"`
	Accounts     map[string]*RouteConfig `json:"accounts"`
}

// ServerConfig struct represents the configuration for the server
type ServerConfig struct {
	DefaultAPIGateway string `json:"default_api_gateway"`
	SyslogServer      string `json:"syslog_server"`
	DNSServer         string `json:"dns_server"`
	DNSDomain         string `json:"dns_domain"`
	Port              string `json:"port"`
	SessionsURL       string `json:"sessions_url"`
	SignalsURL        string `json:"signals_url"`
}

type RouteConfig struct {
	URL    string  `json:"url"`
	Weight float64 `json:"weight"`
}

var (
	AppConfig  *ApplicationConfig
	tempConfig *ApplicationConfig
	configFile string
)

func Setup(config string) error {
	configFile = config
	_, err := LoadConfig()
	if err != nil {
		return err
	}
	return nil
}

// ReloadConfig opens the config file and loads
func ReloadConfig() error {
	tempConfig := AppConfig

	data, err := ioutil.ReadFile(configFile)
	if err != nil {
		return fmt.Errorf("Unable to load config file: [ %s ]", err)

	}
	err = json.Unmarshal(data, &tempConfig)
	if err != nil {
		return fmt.Errorf("Unable to parse config file, will not reload config: [ %s ]", err)
	} else {
		AppConfig = tempConfig
	}
	return nil
}

// LoadConfig loads the config the first time, if the file does not exit it fails
func LoadConfig() (string, error) {
	data, err := ioutil.ReadFile(configFile)
	if err != nil {
		return "Unable to load config file", err
	}
	AppConfig = &ApplicationConfig{}
	err = json.Unmarshal(data, &AppConfig)
	if err != nil {
		return string(data), fmt.Errorf("Unable to parse config: [ %s ]", err)
	}
	return fmt.Sprintf("Config loaded: ", AppConfig), nil
}

// configSignalWatcher will add a signal hook to SIGURS2 to handle reloads of the configuration file
func ConfigSignalWatcher() (string, error) {
	s := make(chan os.Signal, 1)
	signal.Notify(s, syscall.SIGUSR2)
	go func() {
		for {
			<-s
			ReloadConfig()

		}
	}()
	return fmt.Sprintf("Reloaded"), nil
}

example.go

package main

import (
	log "github.com/Sirupsen/logrus"
	configReloader "github.com/johntdyer/configReloader"
	"time"
)

func init() {
	configReloader.Setup("config.json")
	//config.LoadConfig("config/config.json", *ApplicationConfig)
}

func main() {
	go configReloader.ConfigSignalWatcher()
	for {
		time.Sleep(1000 * time.Millisecond)
		log.Println("===> " + configReloader.AppConfig.Config.DefaultAPIGateway)
	}
}