HeartMonitor.period should be an Integer

millisecond times should generally be integers, because any time they
are specified with fractional precision it is probable that the user
believes the units are seconds, and an error should be raised.

IPython/parallel/controller/heartmonitor.py

@@ -23,7 +23,7 b' from zmq.devices import ThreadDevice'
 from zmq.eventloop import ioloop, zmqstream
 
 from IPython.config.configurable import LoggingConfigurable
-from IPython.utils.traitlets import Set, Instance, CFloat
+from IPython.utils.traitlets import Set, Instance, CFloat, Integer
 
 from IPython.parallel.util import asbytes
 
@@ -64,7 +64,7 b' class HeartMonitor(LoggingConfigurable):'
     pongstream: an XREP stream
     period: the period of the heartbeat in milliseconds"""
 
-    period=CFloat(1000, config=True,
+    period = Integer(1000, config=True,
         help='The frequency at which the Hub pings the engines for heartbeats '
         '(in ms)',
     )