Consider:
- n1, n2 in the cluster
- n2 shutdown
- n2 sends gossip shutdown message to n1
- n1 delays processing of the handler of shutdown message
- n2 restarts
- n1 learns new gossip state of n2
- n1 resumes to handle the shutdown message
- n1 will mark n2 as shutdown status incorrectly until n2 restarts again
To prevent this, we can send the gossip generation number along with the
shutdown message. If the generation number does not match the local
generation number for the remote node, the shutdown message will be
ignored.
Since we use the rpc::optional to send the generation number, it works
with mixed cluster.
Fixes#8597Closes#9381
1657e7be14