Provide subscriptions to network config changes

[cthulhu-rider]

Is your feature request related to a problem? Please describe.

there is no current way to subscribe to changes of the NeoFS network settings. This would improve the system's reaction to reconfigs

Describe the solution you'd like

throw per-config notificaitons by the Netmap contract and subscribe to them from the app side

Describe alternatives you've considered

polling, i.e. long delays and often idle requests

Additional context

• SN starts refusing to save some objects after MaxObjectSize increase neofs-node#2910
• Rework network configuration parameters #372

[carpawell]

What it such a notification is missed?

[cthulhu-rider]

wont get any worse than when there are no notifications at all

[carpawell]

I meant it may get better but the current node code expects to miss any number of notifications at any time, so we cannot rely on it until some changes are done on the nodes side.

[cthulhu-rider]

practice shows network config changes extremely rarely. With notifications, nodes could use bigger cache time and catch changes by notifications mostly. Yeah, running node can miss a notification, and it will know about the change later. But normally notifications should not be missed. And this seems a better option than more frequent requests when config stays the same for months

so, worst scenario is not worse while the best one is better. And ur right, this will definitely require catch implementation. The costs seem negligible