Non-voters and automatic promotion

src/ra.erl

@@ -477,13 +477,14 @@ start_server(System, ClusterName, {_, _} = ServerId, Machine, ServerIds) ->
     start_server(System, ClusterName, #{id => ServerId}, Machine, ServerIds);
 start_server(System, ClusterName, #{id := {_, _}} = Conf0, Machine, ServerIds)
   when is_atom(System) ->
-    UId = new_uid(ra_lib:to_binary(ClusterName)),
+    UId = maps:get(uid, Conf0,
+                   new_uid(ra_lib:to_binary(ClusterName))),
     Conf = #{cluster_name => ClusterName,
              uid => UId,
              initial_members => ServerIds,
              log_init_args => #{uid => UId},
              machine => Machine},
-    start_server(System, maps:merge(Conf, Conf0)).
+    start_server(System, maps:merge(Conf0, Conf)).
 
 %% @doc Starts a ra server in the default system
 %% @param Conf a ra_server_config() configuration map.
@@ -1134,15 +1135,15 @@ key_metrics({Name, N} = ServerId) when N == node() ->
     case whereis(Name) of
         undefined ->
             Counters#{state => noproc,
-                      non_voter => noproc};
+                      membership => unknown};
         _ ->
             case ets:lookup(ra_state, Name) of
                 [] ->
                     Counters#{state => unknown,
-                              non_voter => unknown};
-                [{_, State, NonVoter}] ->
+                              membership => unknown};
+                [{_, State, Membership}] ->
                     Counters#{state => State,
-                              non_voter => NonVoter}
+                              membership => Membership}
             end
     end;
 key_metrics({_, N} = ServerId) ->

src/ra.hrl

@@ -43,18 +43,19 @@
 %% Subset of  ra_server:ra_server_config().
 %% Both `ra:add_member` and `ra:start_server` must be called with the same values.
 -type ra_new_server() :: #{id := ra_server_id(),
-
-                           %% If set, server will start as non-voter until later promoted by the
-                           %% leader.
-                           non_voter => boolean(),
+                           % Defaults to `voter` is absent.
+                           membership => ra_membership(),
+                           % Required for `promotable` in the above.
                            uid => ra_uid()}.
 
 -type ra_peer_status() :: normal |
                           {sending_snapshot, pid()} |
                           suspended |
                           disconnected.
 
--type ra_voter_status() :: #{non_voter => boolean(),
+-type ra_membership() :: voter | promotable | non_voter | unknown.
+
+-type ra_voter_status() :: #{membership => ra_membership(),
                              uid => ra_uid(),
                              target => ra_index()}.
 
@@ -64,15 +65,19 @@
                            % the commit index last sent
                            % used for evaluating pipeline status
                            commit_index_sent := non_neg_integer(),
-                           %% whether the peer is part of the consensus
-                           voter_status := ra_voter_status(),
+                           %% Whether the peer is part of the consensus.
+                           %% Defaults to "yes" if absent.
+                           voter_status => ra_voter_status(),
                            %% indicates that a snapshot is being sent
                            %% to the peer
                            status := ra_peer_status()}.
 
 -type ra_cluster() :: #{ra_server_id() => ra_peer_state()}.
 
--type ra_cluster_servers() :: [ra_server_id()].
+%% Dehydrated cluster:
+-type ra_cluster_servers() :: [ra_server_id()].  % Deprecated
+-type ra_peer_snapshot() :: #{voter_status => ra_voter_status()}.
+-type ra_cluster_snapshot() :: #{ra_server_id() => ra_peer_snapshot()}.
 
 %% represent a unique entry in the ra log
 -type log_entry() :: {ra_index(), ra_term(), term()}.
@@ -154,8 +159,7 @@
 
 -type snapshot_meta() :: #{index := ra_index(),
                            term := ra_term(),
-                           cluster := ra_cluster_servers(),
-                           cluster_state => ra_cluster(),  %% TODO replace `cluster`
+                           cluster := ra_cluster_snapshot(),
                            machine_version := ra_machine:version()}.
 
 -record(install_snapshot_rpc,

src/ra_directory.erl

@@ -188,7 +188,7 @@ overview(System) when is_atom(System) ->
                                pid => Pid,
                                parent => Parent,
                                state => S,
-                               non_voter => V,
+                               membership => V,
                                cluster_name => ClusterName,
                                snapshot_state => maps:get(UId, Snaps,
                                                           undefined)}}

src/ra_log.erl

@@ -637,14 +637,15 @@ update_release_cursor0(Idx, Cluster, MacVersion, MacState,
                        #?MODULE{cfg = #cfg{snapshot_interval = SnapInter},
                                 reader = Reader,
                                 snapshot_state = SnapState} = State0) ->
-    ClusterServerIds = maps:keys(Cluster),
+    ClusterServerIds = maps:map(fun (_, V) ->
+                                        maps:with([voter_status], V)
+                                end, Cluster),
     SnapLimit = case ra_snapshot:current(SnapState) of
                     undefined -> SnapInter;
                     {I, _} -> I + SnapInter
                 end,
     Meta = #{index => Idx,
              cluster => ClusterServerIds,
-             cluster_state => Cluster,
              machine_version => MacVersion},
     % The release cursor index is the last entry _not_ contributing
     % to the current state. I.e. the last entry that can be discarded.