func (s *server) Replica(shard int) error {
role, ok := s.roles[shard]
require.False(s.t, ok, "Replica %d assigned when we're already %s for it.", shard, role)
s.roles[shard] = "replica"
return nil
}
func (s *server) Master(shard int) error {
role, ok := s.roles[shard]
require.False(s.t, ok, "Master %d assigned when we're already %s for it.", shard, role)
s.roles[shard] = "master"
return nil
}