Pulling a snapshot of the raft topology is done via new rpc verb
(RAFT_PULL_TOPOLOGY_SNAPSHOT). If the recipient runs an older version of
scylla and does not understand the verb, sending it will result in an
error. We usually use cluster features to avoid such situations, but in
the case when a node joins the cluster, it doesn't have access to
features yet. Therefore, we need to enable pulling snapshots in two
situations:
- when the SUPPORTS_CONSISTENT_TOPOLOGY_CHANGES feature becomes enabled,
- in case when starting group 0 server when joining a cluster that uses
raft-based topology.
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