code: def getInstanceJstack(self, topology_info, instance_id):
      
      pid_response = yield getInstancePid(topology_info, instance_id)
      try:
        http_client = tornado.httpclient.AsyncHTTPClient()
        pid_json = json.loads(pid_response)
        pid = pid_json['stdout'].strip()
        if pid == '':
          raise Exception('Failed to get pid')
        endpoint = utils.make_shell_endpoint(topology_info, instance_id)
        url = "%s/jstack/%s" % (endpoint, pid)
        response = yield http_client.fetch(url)
        Log.debug("HTTP call for url: %s", url)
        raise tornado.gen.Return(response.body)
      except tornado.httpclient.HTTPError as e:
        raise Exception(str(e))
docs: Fetches Instance jstack from heron-shell.