Have you considered anti-DDoS services or CDNs like CloudFlare? I don't want to sound disrespectful, but based on your question and reply you don't seem to be up to the very difficult task at hand. We'd be talking of mitigation techniques that go beyond the capability of typical hosted web applications, WAFs, distributed and/or load-balanced setups and alike. It has fairly little to do with your selection of server-side scripting language, or indeed web application itself, and not doing this right only makes it more likely that your service will end up being an even easier target. —
TildalWave 44 secs ago