This is a Node.js application that generates a unique numeric ID. It uses the time in microseconds, the unique instance ID of this server and a counter to cater for sub-millisecond accesses. These are joined to form a value that is passed back in json format.
It is similar in concept to Twitter's Snowflake project. Just a lot less code and more limitations. It only handles 16 application instances (starting at 0) and only copes with 256 iterations within a single millisecond with rollover protection.
It can generate just over 6000 IDs/second on my 13" Macbook Pro.
The unique instance ID is hard-coded. It is trivial to pass through an ID as a startup argument and then initialize the id variable to this value:
var id = process.argv[2];
However, a better approach would be to allow the application to call a service to obtain its unique instance ID. This service would track the IP address of the calling application and would allocate an ID to the service. This could be implemented in many ways. This assumes you have a single instance of this application running on an IP address.
Another limitation is Javascript's handling of large numbers. The reason the instance ID is restricted to the number 15 and the sequence counter to the number 255 is that shifting the timestamp too many bits left causes an overflow. It is possible that the timestamp may become too large and cause this overflow to occur even with the currently imposed limits. This will happen around the year 2079. If you adjust the starting epoch you could get around 69 years of reliable use.
One more limitation is that the date and times on each server running an instance of this application must be synchronized and accurate for the ordering of generated ID values to work well.