Optionally specify the availability zone within the region. This can be important if you are using an Amazon EC2 instance in conjunction with an EBS volume. In this case both the EBS volume and EC2 instance must be in the same availability zone. See the AWS documentation for more about what availability zones are. (For the moment you must look up the available zones for the region yourself and type in the zone name, in the future, we plan to have this be a list you can select from).