Push notifications from the server to the mobile client. How to implement?

Question

PHP

Good afternoon.
There is a task. Imagine that there is some server part and many mobile clients that pull information from there.
Requests are usually simple: select, create, update. But there is a feature. When creating an entity, you need to track its status. The status code is binary, 0 or 1. When creating an entity, the mobile client receives its uid. It is necessary that the mobile client receive information about the change in the status of its entity as soon as possible.
Polling the server is bad. With an increase in the number of mobile clients, the server will not survive.
What are the solutions if:
1) The server part in PHP
2) Any mobile clients (iOS, Android, Win, etc.)
3) Potentially, the same functionality for the web muzzle will be required.

Answer 1

for websockets + fallback in long pooling, for ios, android and win, Apple push notifications, Google Cloud Messages and Windows Push Notification Services respectively. Or websockets and casters.
aws.amazon.com/sns is an easier solution.
pusher.com
There are a lot of them...

Answer 2

For mobile applications, I would use native push services.
For a website, some crutches on sockets.
It is convenient to do this on node.js + socket.io