FAAS Heroku as a Function (HAAF) runs your collection of request handlers without concerning you with the underlying server. Serverless? It's certainly less server.
You write nodejs functions as Koa request handlers. See functions/example.js
.
const verb = 'get'
const path = '/'
const fctn = (ctx) => { ctx.body = "wubalubadubdub" }
module.exports = [verb, path, fctn]
Thanks to Heroku Autoscaling your functions can dynamically grow/shrink inline with demand. Classic Heroku.