Action Server timeout across systems

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I am having trouble with actionlib.SimpleActionClient wait_for_server timing out when the client and server are on different systems and I could use help understanding why. In this case, roscore and the action server is running on a Raspberry Pi and the client is running on an Ubuntu VM. Both are running Indigo. I have a simple example that runs fine when the client and server run on the same computer (the Raspberry Pi). However when I run roscore and the action server on the Raspberry Pi and I run these commands on the Ubuntu client side:

• rosnode list correctly lists the server node
• rostopic list correctly lists the topics
• rosnode ping ping_action_server shows repeated successful pings of about 20 msecs

However, when I run the following client code it fails to connect...

import sys
import rospy
import actionlib

from inmoov.msg import PingAction, PingGoal, PingResult

def onShutdown():
    rospy.loginfo("Shutting down")

try:  
    rospy.init_node('ping_client', log_level=rospy.DEBUG)
    rospy.on_shutdown(onShutdown)
    client = actionlib.SimpleActionClient('ping', PingAction)
    rospy.loginfo("Waiting for ping action server...")
    finished = client.wait_for_server(timeout = rospy.Duration(10.0))
    if(finished is False): 
        rospy.logerr("Ping action server timed out")
    else:
        rospy.loginfo("Ping action server found")

except:
    print("An exception was encountered")
    e = sys.exc_info()[0]
    print str(e)

The output is:

[DEBUG] [WallTime: 1473631183.986657] init_node, name[/ping_client], pid[7947]
[DEBUG] [WallTime: 1473631183.987061] binding to 0.0.0.0 0
[DEBUG] [WallTime: 1473631183.987256] bound to 0.0.0.0 35061
[DEBUG] [WallTime: 1473631183.987703] ... service URL is rosrpc://raspberrypi:35061
[DEBUG] [WallTime: 1473631183.987884] [/ping_client/get_loggers]: new Service instance
[DEBUG] [WallTime: 1473631184.003141] ... service URL is rosrpc://raspberrypi:35061
[DEBUG] [WallTime: 1473631184.003397] [/ping_client/set_logger_level]: new Service instance
[INFO] [WallTime: 1473631184.130352] Waiting for ping action server...
[DEBUG] [WallTime: 1473631184.131371] connecting to raspberrypi 52197
[DEBUG] [WallTime: 1473631184.131768] connecting to raspberrypi 52197
[DEBUG] [WallTime: 1473631184.152471] connecting to raspberrypi 52197
[ERROR] [WallTime: 1473631194.139802] Ping action server timed out
[INFO] [WallTime: 1473631194.140166] Shutting down
[DEBUG] [WallTime: 1473631194.192350] connecting to raspberrypi 52197
[DEBUG] [WallTime: 1473631194.193241] connecting to raspberrypi 52197

Any ideas would be appreciated. If it matters, I have a ROS publisher that runs on the Ubuntu VM and a ROS Subscriber on the Raspberry Pi that successfully receives the published messages. The Raspberry Pi has a static IP and the Ubuntu VM has an entry in /etc/hosts to map the static IP to the host name "raspberrypi".

Here are the Ubuntu environment settings:

mike@badmonkey:~$ printenv | grep ROS
ROS_ROOT=/opt/ros/indigo/share/ros
ROS_PACKAGE_PATH=/home/mike/catkin_ws/src:/opt/ros/indigo/share:/opt/ros/indigo/stacks
ROS_MASTER_URI=http://raspberrypi:11311
ROS_HOSTNAME=raspberrypi
ROSLISP_PACKAGE_DIRECTORIES=/home/mike/catkin_ws/devel/share/common-lisp
ROS_DISTRO=indigo
ROS_LANG_DISABLE=genlisp
ROS_ETC_DIR=/opt/ros/indigo/etc/ros