One more working solution: wokeDyno Here is a blog post how it works: It's integrated in the app very easy:
/* Example: as used with an Express app */
const express = require("express")
const wakeDyno = require("woke-dyno");
// create an Express app
const app = express();
// start the server, then call wokeDyno(url).start()
app.listen(PORT, () => {
wakeDyno(DYNO_URL).start(); // DYNO_URL should be the url of your Heroku app
});