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Add ROS 2 CLI module to Fast DDS Discovery Server Tutorial (#16)
* Refs #17064: Add ROS 2 CLI module to Fast DDS Discovery Server Tutorial Signed-off-by: Mikel Rico <[email protected]> * Refs #17064: ROS2 repo suggestions: A publisher is a communication interface, not a node. Signed-off-by: Mikel Rico <[email protected]> * Refs #17064: ROS2 repo suggestions: Nits Signed-off-by: Mikel Rico <[email protected]> * Refs #17064: ROS2 repo suggestions: Network graph Signed-off-by: Mikel Rico <[email protected]> * Refs #17064: Applied suggestions Signed-off-by: Mikel Rico <[email protected]> * Refs #17064: Nitpicks Signed-off-by: Mikel Rico <[email protected]> --------- Signed-off-by: Mikel Rico <[email protected]>
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‎source/Tutorials/Advanced/Discovery-Server/Discovery-Server.rst

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@@ -51,7 +51,7 @@ The following figure shows the decrease in discovery messages:
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This architecture reduces the number of messages sent between the server and clients dramatically.
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In the following graph, the reduction in network traffic over the discovery phase for the `RMF Clinic demonstration <https://github.com/osrf/rmf_demos>`__ is shown:
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In the following graph, the reduction in network traffic over the discovery phase for the `RMF Clinic demonstration <https://github.com/open-rmf/rmf_demos#Clinic-World>`__ is shown:
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.. image:: figures/discovery_server_v2_performance.svg
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ROS 2 Introspection
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-------------------
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ROS 2 Command Line Interface (CLI) implements several introspection tools to analyze the behaviour of a ROS 2 network.
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These tools (i.e. ``ros2 bag record``, ``ros2 topic list``, etc.) are very helpful to understand a ROS 2 working network.
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Most of these tools use DDS simple discovery to exchange topic information with every existing participant (using simple discovery, every participant in the network is connected with each other).
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However, the new Discovery Server v2 implements a network traffic reduction scheme that limits the discovery data between participants that do not share a topic.
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This means that not every node will receive every topic's discovery data unless it has a reader for that topic.
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As most ROS 2 CLIs need a node in the network (some of them rely on a running ROS 2 daemon, and some create their own nodes), using the Discovery Server v2 these nodes will not have all the network information, and thus their functionalities are limited.
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The Discovery Server v2 functionality allows every Participant running as a **SUPER_CLIENT**, a kind of **Client** that connects to a **SERVER**, from which it receives all the available discovery information (instead of just what it needs).
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In this sense, ROS 2 introspection tools can be configured as **Super Client**, thus being able to discover every entity that is using the Discovery Server protocol within the network.
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.. note::
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In this section we use the term *Participant* as a DDS entity. Each DDS *Participant* corresponds with a ROS 2 *Context*, a ROS 2 abstraction over DDS.
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`Nodes <ROS2Nodes>` are ROS 2 entities that rely on DDS communication interfaces: ``DataWriter`` and ``DataReader``.
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Each *Participant* can hold multiple ROS 2 Nodes.
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For further details about these concepts, please visit the `Node to Participant mapping design document <http://design.ros2.org/articles/Node_to_Participant_mapping.html>`__
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Daemon's related tools
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^^^^^^^^^^^^^^^^^^^^^^
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The ROS 2 Daemon is used in several ROS 2 CLI introspection tools.
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It creates its own Participant to add a ROS 2 Node to the network graph, in order to receive all the data sent.
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In order for the ROS 2 CLI to work when using Discovery Server mechanism, the ROS 2 Daemon needs to be
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configured as **Super Client**.
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Therefore, this section is devoted to explain how to use ROS 2 CLI with ROS 2 Daemon running as a **Super Client**.
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This will allow the Daemon to discover the entire Node graph, and to receive every topic and endpoint information.
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To do so, a Fast DDS XML configuration file is used to configure the ROS 2 Daemon and CLI tools.
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.. warning::
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Although it is possible to run the ROS 2 Daemon as a **Server**, this is not recommended since the daemon will stop
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after two hours of inactivity, taking the **Server** down with it.
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Below you can find a XML configuration profile, which for this tutorial should be saved in the working directory as ```super_client_configuration_file.xml``` file.
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This file will configure every new participant using it, as a **Super Client**.
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.. code-block:: xml
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<?xml version="1.0" encoding="UTF-8" ?>
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<dds>
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<profiles xmlns="http://www.eprosima.com/XMLSchemas/fastRTPS_Profiles">
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<participant profile_name="super_client_profile" is_default_profile="true">
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<rtps>
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<builtin>
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<discovery_config>
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<discoveryProtocol>SUPER_CLIENT</discoveryProtocol>
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<discoveryServersList>
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<RemoteServer prefix="44.53.00.5f.45.50.52.4f.53.49.4d.41">
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<metatrafficUnicastLocatorList>
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<locator>
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<udpv4>
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<address>127.0.0.1</address>
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<port>11811</port>
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</udpv4>
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</locator>
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</metatrafficUnicastLocatorList>
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</RemoteServer>
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</discoveryServersList>
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</discovery_config>
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</builtin>
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</rtps>
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</participant>
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</profiles>
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</dds>
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.. note::
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Under the *RemoteServer* tag, the *prefix* attribute value should be updated according to the server ID passed on the CLI (see `Fast DDS CLI <https://fast-dds.docs.eprosima.com/en/latest/fastddscli/cli/cli.html#discovery>`__).
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The value specified in the shown XML snippet corresponds to an ID of value 0.
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First of all, instantiate a Discovery Server using `Fast DDS CLI <https://fast-dds.docs.eprosima.com/en/latest/fastddscli/cli/cli.html#discovery>`__ specifying an ID of value 0.
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.. code-block:: console
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fastdds discovery -i 0 -l 127.0.0.1 -p 11811
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Run a talker and a listener that will discover each other through the Server (notice that ``ROS_DISCOVERY_SERVER`` configuration is the same as the one in ``super_client_configuration_file.xml``).
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.. code-block:: console
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export ROS_DISCOVERY_SERVER="127.0.0.1:11811"
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ros2 run demo_nodes_cpp listener --ros-args --remap __node:=listener
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.. code-block:: console
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export ROS_DISCOVERY_SERVER="127.0.0.1:11811"
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ros2 run demo_nodes_cpp talker --ros-args --remap __node:=talker
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Then, instantiate a ROS 2 Daemon using the **Super Client** configuration (remember to source ROS 2 installation in every new terminal).
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.. code-block:: console
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export FASTRTPS_DEFAULT_PROFILES_FILE=super_client_configuration_file.xml
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ros2 daemon stop
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ros2 daemon start
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ros2 topic list
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ros2 node info /talker
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ros2 topic info /chatter
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ros2 topic echo /chatter
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We can also see the Node's Graph using the ROS 2 tool ``rqt_graph`` as follows (you may need to press the refresh button):
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.. code-block:: console
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export FASTRTPS_DEFAULT_PROFILES_FILE=super_client_configuration_file.xml
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rqt_graph
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No Daemon tools
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^^^^^^^^^^^^^^^
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Some ROS 2 CLI tools do not use the ROS 2 Daemon.
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In order for these tools to connect with a Discovery Server and receive all the topics information they need to be instantiated as a **Super Client** that connects to the **Server**.
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Following the previous configuration, build a simple system with a talker and a listener.
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First, run a **Server**:
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.. code-block:: console
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fastdds discovery -i 0 -l 127.0.0.1 -p 11811
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Then, run the talker and listener in separate terminals:
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.. code-block:: console
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export ROS_DISCOVERY_SERVER="127.0.0.1:11811"
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ros2 run demo_nodes_cpp listener --ros-args --remap __node:=listener
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.. code-block:: console
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export ROS_DISCOVERY_SERVER="127.0.0.1:11811"
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ros2 run demo_nodes_cpp talker --ros-args --remap __node:=talker
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Continue using the ROS 2 CLI with ``--no-daemon`` option with the new configuration.
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New nodes will connect with the existing Server and will know every topic.
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Exporting ``ROS_DISCOVERY_SERVER`` is not needed as the ROS 2 tools will be configured through the ``FASTRTPS_DEFAULT_PROFILES_FILE``.
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.. code-block:: console
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export FASTRTPS_DEFAULT_PROFILES_FILE=super_client_configuration_file.xml
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ros2 topic list --no-daemon
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ros2 node info /talker --no-daemon --spin-time 2
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Compare Fast DDS Discovery Server with Simple Discovery Protocol
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----------------------------------------------------------------
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In order to compare executing nodes using the Simple Discovery Protocol (the default DDS mechanism for distributed discovery) or the discovery server, two scripts that execute a talker and many listeners and analyze the network traffic during this time are provided.
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In order to compare executing nodes using the *Simple Discovery* Protocol (the default DDS mechanism for distributed discovery) or the *Discovery Server*, two scripts that execute a talker and many listeners and analyze the network traffic during this time are provided.
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For this experiment, ``tshark`` is required to be installed on your system.
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The configuration file is mandatory in order to avoid using intraprocess mode.
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