Integrate Push Notifications for Android Firebase

问题:

We are building a real time chat application for businesses to connect to their consumers. For now we are using Firebase (https://www.firebase.com/) as the backend for the prototype and it seems to be working fine. However we have run into a major roadblock in terms of push notifications. What is the best method to integrate push notifications in a chat application for each new message using Firebase as the backend?

I have read somewhere that you can set up a Heroku Node.JS server to listen for push notifications, however we are unable to find any specific steps to do so. Also, is this a viable solution in terms of cost and scalability? We envision millions of users on the platform at some stage.

Please let me know if there is any alternate solution that we can use.

Thanks.