zookeeper on ec2

[David Graf]

Hello

I wanna set up a zookeeper ensemble on amazon's ec2 service. In my  
system, zookeeper is used to run a locking service and to generate  
unique id's. Currently, for testing purposes, I am only running one  
instance. Now, I need to set up an ensemble to protect my system  
against crashes.
The ec2 services has some differences to a normal server farm. E.g.  
the data saved on the file system of an ec2 instance is lost if the  
instance crashes. In the documentation of zookeeper, I have read that  
zookeeper saves snapshots of the in-memory data in the file system. Is  
that needed for recovery? Logically, it would be much easier for me if  
this is not the case.
Additionally, ec2 brings the advantage that serves can be switch on  
and off dynamically dependent on the load, traffic, etc. Can this  
advantage be utilized for a zookeeper ensemble? Is it possible to add  
a zookeeper server dynamically to an ensemble? E.g. dependent on the  
in-memory load?

David