I use constructor to generate repo. But it is not worth to do + it was a Singleton so we don't need a constructor to create new Object

I think some of the action is frequently consume DB even if there is no update. So I think it's good to cache it. I will try to use redis for the solution

I use bluebird to promisify my database connection object. It working properly, but it show warning that it was vulnerable

I have create a simple async handler. But I don't know how to report to client if there are an error when the client push an event into the system. So I just log the error for now.