How to create a unique identifier in a cluster of web servers

Question

In the following scenario:

1 Database 4 Web Servers

How do web servers generate a unique identifier for the database to be unique? Yes, it is possible to use Auto-increment, but it is too easy to scan / guess / etc. Thus, auto-increment is currently not an option.

Answer 1

Use the UUID ( http://www.ietf.org/rfc/rfc4122.txt ). Collisions are unlikely and can be considered when they occur by regenerating a new UUID, or they can be prevented by combining a unique identifier for each server (for example, MAC address): -

StringBuilder sb = new StringBuilder(UUID.randomUUID());
InetAddress address = InetAddress.getLocalHost();
String uid = sb.append(NetworkInterface.getByInetAddress(address).getHardwareAddress());

Answer 2

You can use UUID:

import java.util.UUID;        

UUID uuid = UUID.randomUUID();
System.out.println(uuid.toString());

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