how etcd raft persist raft topology and membership change

[Jia]

Hello,

I am trying to understand how membership change works in etcd-raft and have some questions here. 

Correct me if I am wrong, it seems etcd-raft does not explicitly persist the raft topology, but instead treat each membership change as a raft log entry. I am looking at the node implementation of etcd-raft. Apparently, when starting a new node, it manually injects a configChangeEntry; and when restarting a node, it relies on replaying WAL logs from the very beginning to obtain peer information. 

However, what happens if we have a persisted appliedIndex, in which case raft won't re-apply all the logs from index 1? How does it know its peer information in order to join the group?

Thanks a lot. 

Jia

[anthony...@coreos.com]

Cluster membership information is stored to etcd's storage backend. The persisting is done in https://github.com/coreos/etcd/tree/master/etcdserver/membership (in particular, store.go)

[Jia]

Thanks! Good to know. The raftExample does not handle that, so we'll need to persist the configState accordingly.