The patch adds the `SUPPORTS_RAFT_CLUSTER_MANAGEMENT`
and `USES_RAFT_CLUSTER_MANAGEMENT` gossiper features.
These features provide a way to organize the automatic
switch to raft-based cluster management.
The scheme is as follows:
1. Every new node declares support for raft-based cluster ops.
2. At the moment, no nodes in the cluster can actually use
raft for cluster management, until the `SUPPORTS*` feature is enabled
(i.e. understood by every node in the cluster).
3. After the first `SUPPORTS*` feature is enabled, the nodes
can declare support for the second, `USES*` feature, which
means that the node can actually switch to use raft-based cluster
ops.
The scheme ensures that even if some nodes are down while
transitioning to new bootstrap mechanism, they can easily
switch to the new procedure, not risking to disrupt the
cluster.
The features are not actually wired to anything yet,
providing a framework for the integration with `raft_group0`
code, which is subject for a follow-up series.
Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com>
Message-Id: <20211220081318.274315-1-pa.solodovnikov@scylladb.com>
904de0a094