1. A method for generating a unique identifier of a distributed computing system consisting of a plurality of virtual machines including a first virtual machine, a second virtual machine and an identifier allocation server, the method comprising: receiving, by the first virtual machine, a first index range allocated by the identifier allocation server; receiving, by the second virtual machine, a second index range allocated by the identifier allocation server, the second index range being different from the first index range; generating, by the first virtual machine, a first unique identifier using an index in the first index range without intervention of the identifier allocation server; and generating, by the second virtual machine, a second unique identifier using an index in the second index range without intervention of the identifier allocation server, wherein the first unique identifier and the second unique identifier are identifiers satisfying uniqueness for the whole distributed computing system.