import (
    "fmt"

    "github.com/coreos/go-etcd/etcd"
    "github.com/mcuadros/go-etcd-hydrator"
)

type MyAppConfig struct {
    Rest string //<-- the hydrator will ask to etcd for `rest` key
    MongoDB string `etcd:"mongo.host"` //<--  ask to etcd for `mongo.host` key
}

func NewMyAppConfig() *MyAppConfig {
    example := new(MyAppConfig)

    h := NewHydrator(etcd.NewClient([]string{"http://127.0.0.1:2379"}))
    h.Hydrate(foo)

    return example
}

...
config := NewMyAppConfig()
fmt.Println(config.Rest) //Prints: http://rest.company.com
fmt.Println(config.MongoDB) //Prints: 127.0.0.1:27017