code: def router_add(self, params):
          
          if self.uses_rs_configdb:
              # Replica set configdb.
              rs_id = self._configsvrs[0]
              config_members = ReplicaSets().members(rs_id)
              configdb = '%s/%s' % (
                  rs_id, ','.join(m['host'] for m in config_members))
          else:
              configdb = ','.join(Servers().hostname(item)
                                  for item in self._configsvrs)
          server_id = params.pop('server_id', None)
          version = params.pop('version', self._version)
          params.update({'configdb': configdb})
  
          if self.enable_ipv6:
              common.enable_ipv6_single(params)
          # Remove flags that turn auth on.
          params = self._strip_auth(params)
  
          self._routers.append(Servers().create(
              'mongos', params, sslParams=self.sslParams, autostart=True,
              version=version, server_id=server_id))
          return {'id': self._routers[-1], 'hostname': Servers().hostname(self._routers[-1])}
docs: add new router (mongos) into existing configuration