API exposed to raft leader when follower node goes down in braft implementation

Nobody has claimed this yet.

I am using Raft (braft library) for high availability. I have 3 applications (Nodes) forming raft cluster. I have to manage application (Node) states (ONLINE, OFFLINE).
If leader goes down and another node becomes leader there are api's exposed to application which becomes leader(on_leader_start()). Similarly does braft provides any api or method
exposed to leader application when follower goes down (Unplanned shutdown) or joins the raft cluster?

For example: I have the following scenarios.

scenario 1.

App1(leader, state: ONLINE), App2(follower, state: ONLINE), App3(follower, state: ONLINE)
App2 goes down (Unplanned shutdown)
I have to manage Node states App1(state: ONLINE), App2(state: OFFLINE), App3(state: ONLINE)
How will braft notify App1(leader) that App2 is down.

scenario 2.

App1(leader, state: ONLINE), App2(follower, state: OFFLINE), App3(follower, state: ONLINE)
App2 rejoins the raft cluster.
I have to manage Node states App1(state: ONLINE), App2(state: ONLINE), App3(state: ONLINE)
How will braft notify App1(leader) that App2 has joined the cluster.

Start with the braft leader callback on_leader_start() and the documented APIs for follower membership or liveness changes. Determine whether braft exposes notifications when a follower shuts down or rejoins, and define how those events should be delivered to the leader application.

Written by the indexing model from the issue text.