compose-pkg-duckietown

Duckietown package for the \compose\ platform implementing Duckieboard, a Remote Dashboard for the Duckietown project.

Duckieboard provides high level fleet management and monitoring capabilities for Duckietown.

Duckietown <-> World

The easiest way to monitor and control a Duckiebot remotely using Duckieboard, thus via the web browser, is to setup a network bridge between the outside world and Duckietown.

Bridging each Duckiebot to the outside world has the main advantage of allowing data to flow directly from the on-board Raspberry Pi to the user's browser. The Duckiebots are bridged using IP Forwarding via a dedicated machine (i.e., network bridge) connected to both Duckietown and internet. Deploying the network bridge on the machine hosting the Duckieboard would allow the use of Duckieboard to easily configure the routing table (iptables) of the network bridge. For the remainder of this document we will refer to the bridge machine as Bridge.

The applications bridged are:

• SSH [RPi port: TCP(22), Bridge port: TCP(41XXX)]
• ROS Bridge [RPi port: TCP(9090), Bridge port: TCP(42XXX)]

where XXX above is a unique ID associated to each Duckiebot.

IP Forwarding

These instructions are based on tests run on Duckiebots and Bridge both running Ubuntu 16.04.

Enabling IP Forwarding (duckieboard)

IP Forwarding is a kernel function that can be enabled on the Bridge server by running

sysctl net.ipv4.ip_forward=1

for a temporary effect or uncomment the line

net.ipv4.ip_forward = 1

in /etc/sysctl.conf for a permanent effect.

Enable IP Masquerade

IP Masquerade allows machines within a private local network (i.e., duckietown) to seamlessly communicate with the outside world via a mid-point machine (i.e., our Bridge machine).

IP Masquerade can be enabled by running the following command on the Bridge machine

iptables -t nat -A POSTROUTING -j MASQUERADE

Bridging an Application

The TCP port AAAA on the Bridge (IP: CCC.CCC.CCC.CCC) can be forwarded (bridged) to the the port BBBB on the Raspberry Pi (IP:DDD.DDD.DDD.DDD) by running the following command on the Bridge.

iptables -t nat -A PREROUTING -p tcp -d CCC.CCC.CCC.CCC --dport AAAA -j DNAT --to-destination DDD.DDD.DDD.DDD:BBBB

Monitoring bridged Applications

The list of all bridged applications can be obtained by running the command

sudo iptables -t nat -L PREROUTING --line-numbers

An example of output is the following

Chain PREROUTING (policy ACCEPT)
num  target     prot opt source               destination
1    DNAT       tcp  --  anywhere             128.135.8.123        tcp dpt:40003 to:192.168.2.53:22

The output of this command will assign to each rule a unique ID (column num) that we can use to delete rules. A rule with ID <N> can be removed by running the command

sudo iptables -t nat -D PREROUTING <N>

Process Manager on Duckieboard

The library supervisor introduces the possibility to use Duckieboard as a process monitor and manager for Duckiebots. supervisor provides an XMLRPC interface. This opens two possibilities, (i) bridging the XMLRPC server to the outside world, (ii) implementing a ROS interface for supervisor that maps XMLRPC resources to ROS Services. In the first case, the Duckieboard will communicate with the supervisor back-end directly via XMLRPC. In the second case, the ROS interface to supervisor will be accessible via ROS Bridge.

I believe that the best option is the latter, that is implementing a ROS interface for supervisor that maps XMLRPC resources to ROS Services (UPDATE: Implemented and available at https://github.com/afdaniele/supervisor_ros ). This option also gives us the possibility to correct some issues with supervisor monitoring the roslaunch process. In fact, roslaunch employs its own process manager to monitor all the nodes it runs. This process manager would normally mask the presence of running nodes to the overhead supervisor process manager.

SSH Console via Duckieboard

The library GateOne (not tested yet) provides an open-source web-based Terminal Emulator and SSH client. It constitutes a good candidate for implementing an SSH terminal on Duckieboard.

(Secure) ROS Bridge

ROS Bridge is an open-source library that allows us to tunnel ROS data through a TCP/UDP/WS connection. We can use it to connect ROS to Duckieboard by tunneling ROS via a WebSocket (WS) connection. roslibjs is a ROS client written in JavaScript that can communicate with ROS Bridge. By default, WSs do not provide security/authentication protocols. Nonetheless, ROS Bridge implements a simple MAC-based OAuth1.0 authentication procedure that uses the rosauth library. The authentication in ROS Bridge is disabled by default, it can be enabled here. For further information about how to construct an authentication token in JS that is compatible with rosauth look at the implementation of rosauth here.