Since there is no database is available, you could always check with the other web servers before using a UID. There could be two ways of implementing this:
- either each server keeps track of every UID used (synchronization errors could occur), or
- each server keeps a list of its own UID's (would longer to generate a UID, and if one server goes offline there could be problems)

Thank you for your reply.How will they communicate with each other ?