anchor.diff:  -type(sync_target() :: ?SYNC_TARGET_BOTH |
                          ?SYNC_TARGET_RING_CUR  |
                          ?SYNC_TARGET_RING_PREV |
  -                       ?SYNC_TARGET_MEMBER).
  +                       ?SYNC_TARGET_MEMBER |
  +                       undefined
  +                       ).
   
   %% Consensus Roles
   -define(CNS_ROLE_LEADER,     'L').
  
positive.code: -type(consensus_role() :: ?CNS_ROLE_LEADER |
                            ?CNS_ROLE_FOLLOWER_1 |
                            ?CNS_ROLE_FOLLOWER_2 |
                            ?CNS_ROLE_OBSERBER).
  
  %% Server Type
  -define(SERVER_MANAGER, 'manager').
  
negative.code: %%--------------------------------------------------------------------
  %%
  -record(redundant_node, {
            node                   :: atom(),    %% node name
            available       = true :: boolean(), %% alive/dead
            can_read_repair = true :: boolean(), %% able to execute read-repair in case of 'Get Operation'
            role                   :: consensus_role() %% consensus's role
           }).
  
  