3. ROS2 Discovery Server Example

In the following snippet we see a yaml file to configure a DDS Router to create a Simple Participant in domain 0 and a Local Discovery Server with ROS 2 configuration.

##################################
# CONFIGURATION VERSION
version: v5.0                                      # 0

##################################
# ALLOWED TOPICS
# Allowing ROS2 HelloWorld demo_nodes topic

allowlist:
  - name: rt/chatter                               # 1
    type: std_msgs::msg::dds_::String_             # 1

##################################
# PARTICIPANTS
participants:

##################################
# SIMPLE PARTICIPANT
# This participant will subscribe to topics in allowlist in domain 0 and listen every message published there

  - name: SimpleROS2                               # 2
    kind: local                                    # 3
    domain: 0                                      # 4

##################################
# ROS DISCOVERY SERVER
# This participant will subscribe to topics in allowlist using Discovery Server protocol as Server

  - name: ServerROS2                               # 5
    kind: local-discovery-server                   # 6
    discovery-server-guid:
      ros-discovery-server: true                   # 7
      id: 1                                        # 8
    listening-addresses:                           # 9
      - domain: localhost                          # 10
        port: 11888                                # 11

3.1. Configuration

3.1.1. Allowed Topics

In this section are the Topics that the DDS Router will route from one Participant to the other. Topic HelloWorldTopic with datatype HelloWorld, and ROS 2 topic rt/chatter with datatype std_msgs::msg::dds_::String_ will be forwarded from one domain to the other, allowing different DDS domains to interact to each other.

allowlist:
  - name: rt/chatter                               # 1
    type: std_msgs::msg::dds_::String_             # 1

3.1.2. Simple Participant

This Participant is configured by a name, a kind and the Domain Id, in this case 0.

  - name: SimpleROS2                               # 2
    kind: local                                    # 3
    domain: 0                                      # 4

3.1.3. Discovery Server Participant

This Participant is configured by a name, a kind and a listening addresses where Discovery Server will expect metatraffic data from clients.

  - name: ServerROS2                               # 5
    kind: local-discovery-server                   # 6
    discovery-server-guid:
      ros-discovery-server: true                   # 7
      id: 1                                        # 8
    listening-addresses:                           # 9
      - domain: localhost                          # 10
        port: 11888                                # 11

3.2. Execute example

For a detailed explanation on how to execute the DDS Router, refer to this section. Execute a ROS 2 demo_nodes_cpp talker in domain 0:

ROS_DOMAIN_ID=0 ros2 run demo_nodes_cpp talker

Execute a ROS 2 demo_nodes_cpp listener using Discovery Server as Discovery Protocol:

ROS_DISCOVERY_SERVER=";127.0.0.1:11888" ros2 run demo_nodes_cpp listener

Execute DDS Router with this configuration file (available in <path/to/ddsrouter_tool>/share/resources/configurations/examples/ros_discovery_server.yaml). Once the DDS Router is running, messages from talker in domain 0 will be forwarded by the Router to the listener using Discovery Server, that will print them in stdout.