I have:
- Signal - Whatsapp - Etesync - Conversations.im - Syncthing
all whitelisted from battery optimisation, and I've not noticed any huge drain (I expected it to be unusable and have to go back to google play services or micro-g).
edit: I missed that the original post was talking about keep-alives and you were probably referring to them. But how app-level optimisations can help with keep-alives?
https://www.tldp.org/HOWTO/TCP-Keepalive-HOWTO/usingkeepaliv...
I suspect the hard bit for normal apps is keeping the app active on the device while it is in the background. Google has their FCM receiver running as a low level service so can make sure it is always running.
https://0xacab.org/leap/bitmask_android/issues/2226#note_921...