Intermittent DefaultCredentialsError on GCE

Original issue: https://github.com/GoogleCloudPlatform/google-cloud-python/issues/4358

After successful use of credentials, _ = google.auth.default(), an application crashes when credentials cannot be detected:

...
  File "/usr/local/lib/python2.7/dist-packages/google/cloud/client.py", line 212, in __init__
    Client.__init__(self, credentials=credentials, _http=_http)
  File "/usr/local/lib/python2.7/dist-packages/google/cloud/client.py", line 125, in __init__
    credentials, _ = google.auth.default()
  File "/usr/local/lib/python2.7/dist-packages/google/auth/_default.py", line 286, in default
    raise exceptions.DefaultCredentialsError(_HELP_MESSAGE)
DefaultCredentialsError: Could not automatically determine credentials. Please set GOOGLE_APPLICATION_CREDENTIALS or
explicitly create credential and re-run the application. For more
information, please see
https://developers.google.com/accounts/docs/application-default-credentials.

/cc @dmho418

[dhendry]

I would love to see a fix for this issue

[ghost]

I’m still seeing this error fairly regularly running on GAE flex for Python 3.6 with google-auth==1.6.3. Here’s the full stack trace:

  ...
  File "/env/lib/python3.6/site-packages/google/auth/transport/requests.py", line 205, in request
    self._auth_request, method, url, request_headers)
  File "/env/lib/python3.6/site-packages/google/auth/credentials.py", line 122, in before_request
    self.refresh(request)
  File "/env/lib/python3.6/site-packages/google/auth/compute_engine/credentials.py", line 102, in refresh
    six.raise_from(new_exc, caught_exc)
  File "<string>", line 3, in raise_from
google.auth.exceptions.RefreshError: HTTPConnectionPool(host='metadata.google.internal', port=80): Max retries exceeded with url: /computeMetadata/v1/instance/service-accounts/[e-mail]/?recursive=true (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7f9964d74080>: Failed to establish a new connection: [Errno 111] Connection refused',))