Merge pull request #176 from lsst-sqre/master

Add check for None as a container status.

kubespawner/spawner.py

@@ -1094,8 +1094,14 @@ def poll(self):
         """
         Check if the pod is still running.
 
-        Returns None if it is, and 1 if it isn't. These are the return values
-        JupyterHub expects.
+        Uses the same interface as subprocess.Popen.poll(): if the pod is
+        still running, returns None.  If the pod has exited, return the
+        exit code if we can determine it, or 1 if it has exited but we
+        don't know how.  These are the return values JupyterHub expects.
+
+        Note that a clean exit will have an exit code of zero, so it is
+        necessary to check that the returned value is None, rather than
+        just Falsy, to determine that the pod is still running.
         """
         # have to wait for first load of data before we have a valid answer
         if not self.pod_reflector.first_load_future.done():
@@ -1104,7 +1110,11 @@ def poll(self):
         if data is not None:
             if data.status.phase == 'Pending':
                 return None
-            for c in data.status.container_statuses:
+            ctr_stat = data.status.container_statuses
+            if ctr_stat is None:  # No status, no container (we hope)
+                # This seems to happen when a pod is idle-culled.
+                return 1
+            for c in ctr_stat:
                 # return exit code if notebook container has terminated
                 if c.name == 'notebook':
                     if c.state.terminated: