gistfile1.txt

var ec2east = new AWS.EC2({region: 'us-east-1'});
var ec2west = new AWS.EC2({region: 'us-west-2'});

for (some stuff) {
  if (instance is master) {
    ec2east.runInstances(...);
  } else if (instance is a backup) {
    // run in secondary AZ
    ec2west.runInstances(...);
  }
}