How to send push notifications from server to Android/iOS app?

Question

Mobile development

I can't google any useful information. From what I googled, some talk about push notifications in offline applications, some talk about using GCM or APNS servers.
Why is it impossible to write a simple server in ruby ​​or puff and connect an application to it? After all, anyone can make a protocol, why these Googles and apples? Also openwork from ms appeared somewhere - for WP.
On what to write the server? On sockets? And how is the idea of ​​Push implemented in general - from the server to the client, if the client is behind NAT without a white IP? Is there a persistent connection or is the client constantly checking for new information on the server?

Answer 1

First you need to figure out what push notifications are and what mechanisms ensure their delivery. Then continue reading the official GCM (or more recently FCM) and APNS docs. After that, it will become clear that your bike will not provide either energy saving on the user's device, or more or less reliable operation. And all you need to do is connect to FCM and APNS, and easily send notifications from your backend to Ruby, Php, .Net or any other language that supports http requests.