Repository: jupyterhub/jupyterhub

Issue:
Possible stack overflow in our exponential backoff algorithm
I did a load test that intentionally failed, and in the hub logs I found a lot of:


```
[E 2017-10-24 01:31:09.942 JupyterHub web:1590] Uncaught exception GET /hub/user/j-b-1-c282/ (10.128.0.3)
    HTTPServerRequest(protocol='http', host='35.194.17.65', method='GET', uri='/hub/user/j-b-1-c282/', version='HTTP/1.1', remote_ip='10.128.0.3', headers={'Cookie': 'jupyter-hub-token="2|1:0|10:1508808392|17:jupyter-hub-token|44:NjY1ZjY3OWEzYzc0NDIyOGFhZDk1ZGUwZGU0ZjU3NTE=|3efc170e7b59a3623911057ac706c0180e83a4f46ad34657d51f921c5d50a5d7"', 'X-Forwarded-Port': '80', 'Host': '35.194.17.65', 'X-Forwarded-For': '10.128.0.3', 'X-Forwarded-Proto': 'http', 'Connection': 'close', 'X-Forwarded-Host': '35.194.17.65'})
    Traceback (most recent call last):
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 710, in get
        raise spawner._spawn_future.exception()
      File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1511, in _execute
        result = yield result
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 717, in get
        yield gen.with_timeout(timedelta(seconds=self.slow_spawn_timeout), spawner._spawn_future)
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/handlers/base.py", line 444, in finish_user_spawn
        yield spawn_future
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/user.py", line 476, in spawn
        raise e
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/user.py", line 450, in spawn
        resp = yield server.wait_up(http=True, timeout=spawner.http_timeout)
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/utils.py", line 180, in wait_for_http_server
        timeout=timeout
      File "/usr/local/lib/python3.5/dist-packages/jupyterhub/utils.py", line 135, in exponential_backoff
        raise TimeoutError(fail_message)
    TimeoutError: Server at http://10.16.3.85:8888/user/j-b-1-c282/ didn't respond in 30 seconds
```

While it's not a stackoverflow in this case, it very well could be if the timeout changes.



Discussion:

Resolving patch:
diff --git a/jupyterhub/handlers/base.py b/jupyterhub/handlers/base.py
--- a/jupyterhub/handlers/base.py
+++ b/jupyterhub/handlers/base.py
@@ -3,6 +3,7 @@
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
 
+import copy
 import re
 from datetime import timedelta
 from http.client import responses
@@ -705,9 +706,11 @@ def get(self, name, user_path):
                 # Condition: spawner not active and _spawn_future exists and contains an Exception
                 # Implicit spawn on /user/:name is not allowed if the user's last spawn failed.
                 # We should point the user to Home if the most recent spawn failed.
+                exc = spawner._spawn_future.exception()
                 self.log.error("Preventing implicit spawn for %s because last spawn failed: %s",
-                    spawner._log_name, spawner._spawn_future.exception())
-                raise spawner._spawn_future.exception()
+                    spawner._log_name, exc)
+                # raise a copy because each time an Exception object is re-raised, its traceback grows
+                raise copy.copy(exc).with_traceback(exc.__traceback__)
 
             # check for pending spawn
             if spawner.pending and spawner._spawn_future:


Test patch: