What is the best technology for delivering notifications to an Android client to solve the problem?

Question

Android

At the moment there is a node+express+socket.io backend. The android application (corporate application) has a socket.io client that constantly keeps a connection with the ws server in the foreground service. It's not cool, because consumes a lot of energy and quickly drains the battery, + no 100% stability (there are problems with the death of the session, after which it does not properly resume it, and you need to send additional http requests).
I would like to get rid of a permanent connection, if possible, and the foreground service, thereby increasing the stability and lifetime (stability is more important, but you can donate a battery). To do this, I admit, use another technology for delivering notifications instead of WS, which one - I need your advice. I myself look towards firebase, but I don’t know how good this solution is.
The task is this: you need to send notifications from the back to a specific client (uid in the database) or a group of clients (group-id, which corresponds to several uid clients). At the same time, the delivery of notifications must be timely, no more than 30 seconds from the moment of sending, while the device screen can be blocked for several hours without waking up (we assume that there is always an Internet connection, but if the message was sent at a time when the client is not there was a connection, the notification should still come).
Throw off tips/ideas, share your experience)

Answer 1

Firebase, in fact, even according to the requirements, it just fits. The technology, moreover, is native, it connects in a few clicks.