What technologies do social networks and instant messengers use to implement instant messages?

Question

Notifications

Hello. How in social networks (for example, in VK) is personal correspondence implemented? Are they using websockets? and, if so, are they used both in the desktop version of the site and in the mobile (mobile application)? Also interested in the implementation of correspondence in messengers - also web sockets or something more tricky? Please conduct an educational program

Answer 1

How in social networks (for example, in VK) is personal correspondence implemented?

For websites, there are restrictions on the technologies used.
Whereas applications can use a much wider range of technologies. And if mobile applications are still somewhat limited, then desktop applications are not limited at all.
WebSocket is a crutch, bypassing the limitations of HTTP technology.
Where there are no such restrictions, there is no need to use this crutch.
Hence the conclusion - websocket - for websites, first of all.
In others, perhaps for reasons of minimizing the work of server-side programmers (all types of applications will use the same type of connection to the server), it makes sense to use websocket. However, this will be a problem on mobile devices.
But generally speaking, if the team has resources for development, then websocket is not needed either on mobile phones or on desktop. The use of more appropriate technologies allows more efficient use of resources.
Of the features of mobile phones, Android / iOS notifications can be associated with messages (Telegrams definitely use them).
For example, notification + REST gives quite a prompt response. Without WebSocket.
Well, for desktops, in general, you can do it on bare TCP.

Answer 2

Yes, yes, not necessarily

Answer 3

Erlang