gistfile1.py

def launch_slaves(self, instance_template):
    instances = self.cluster.check_running(NAMENODE, 1)
    if not instances:
      return
    master = instances[0]
    for role in (NAMENODE, JOBTRACKER): 
      singleton_host_env = "%s_HOST=%s" % \
              (self._sanitize_role_name(role), master.public_ip)
      instance_template.add_env_strings(singleton_host_env)
      print singleton_host_env
    self._launch_instances(instance_template)              
    self._attach_storage(instance_template.roles)
    self._print_master_url()