code: def find_existing(self):
          
          instances = self.consul.find_servers(self.tags)
          maxnames = len(instances)
          while instances:
              i = instances.pop(0)
              server_id = i[A.server.ID]
              if self.namespace.add_if_unique(server_id):
                  log.info('Found existing server, %s' % server_id)
                  self.server_attrs = i
                  break
              if len(self.namespace.names) >= maxnames:
                  break
              instances.append(i)
docs: Searches for existing server instances with matching tags.  To match,
          the existing instances must also be "running".