Connecting ROS 2 Nodes with the ROS_DISCOVERY_SERVER env

info

• Level: 🌴 easy
• Compatible ROS distributions: ROS 2 Jazzy, ROS 2 Iron
• Compatible RMW implementations: rmw_fastrtps_cpp

Fast DDS provides an alternative discovery mechanism based on Discovery Server. In addition to its performance benefits, it offers an easy way to connect ROS 2 nodes running on different Husarnet-connected hosts.

This approach is superior to using the ROS_STATIC_PEERS environment variable because it allows new hosts to join the ROS 2 network dynamically without requiring the nodes on all peers to be restarted with an updated ROS_STATIC_PEERS. In its minimal configuration, ROS_DISCOVERY_SERVER requires only one peer to act as a Discovery Server; however, you can add multiple such peers as a backup option.

The ROS_SUPER_CLIENT environment variable, as used in the example, can launch a DDS entity as a Super Client with more discovery information (without setting the ROS_SUPER_CLIENT environment variable to TRUE, you will not see all ROS 2 topics with ros2 topic list).

Examples

Below is a demonstration using a talker-listener ROS 2 demo. Assume that ds-host, talker-host and listener-host are Husarnet hostnames of the three devices in the same Husarnet group:

Host Setup

"Discovery Server" host

This FastDDS CLI command runs the Discovery Server on an arbitrarily chosen host within the Husarnet group. You can execute it on any host, such as your laptop, a random Husarnet-connected server, or directly on the robot with the following command in the terminal:

joe@ds-host

fastdds discovery -i 0 -l husarnet-local -p 11811

This command starts the Discovery Server with id=0, listening for connections on the IPv6 address provided by Husarnet (husarnet-local is an alternative hostname to ds-host in this example) on port 11811.

tip

The host running the Discovery Server can simultaneously run ROS 2 nodes:

joe@ds-host

export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
export ROS_SUPER_CLIENT=TRUE
export ROS_DISCOVERY_SERVER=ds-host:11811

ros2 run demo_nodes_cpp listener

"talker" host

Execute the following commands in the terminal:

bob@talker-host

export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
export ROS_SUPER_CLIENT=TRUE
export ROS_DISCOVERY_SERVER=ds-host:11811

ros2 run demo_nodes_cpp talker

"listener" host

Execute the following commands in the terminal:

kate@listener-host

export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
export ROS_SUPER_CLIENT=TRUE
export ROS_DISCOVERY_SERVER=ds-host:11811

ros2 run demo_nodes_cpp listener

Docker Setup

"Discovery Server" host

Create the following file:

compose.yaml

services:
  ds:
    image: ros:jazzy-ros-core
    network_mode: host
    command: fastdds discovery -i 0 -l husarnet-local -p 11811

Then, execute the following command:

joe@ds-host

docker compose up

"talker" host

Create the following two files in the same directory:

Dockerfile

FROM ros:jazzy-ros-core

RUN apt update && apt install -y \
        ros-${ROS_DISTRO}-demo-nodes-cpp && \
    rm -rf /var/lib/apt/lists/*

compose.yaml

name: ${CHATTER_ROLE:-talker}

services:
  chatter:
    build: .
    network_mode: host
    environment:
      - RMW_IMPLEMENTATION=rmw_fastrtps_cpp
      - ROS_DISCOVERY_SERVER=ds-host:11811
    command: ros2 run demo_nodes_cpp ${CHATTER_ROLE:-talker}

Then, execute the following command:

bob@talker-host

CHATTER_ROLE=talker docker compose up --build --force-recreate

"listener" host

Create the following two files in the same directory:

Dockerfile

FROM ros:jazzy-ros-core

RUN apt update && apt install -y \
        ros-${ROS_DISTRO}-demo-nodes-cpp && \
    rm -rf /var/lib/apt/lists/*

compose.yaml

name: ${CHATTER_ROLE:-talker}

services:
  chatter:
    build: .
    network_mode: host
    environment:
      - RMW_IMPLEMENTATION=rmw_fastrtps_cpp
      - ROS_DISCOVERY_SERVER=ds-host:11811
    command: ros2 run demo_nodes_cpp ${CHATTER_ROLE:-talker}

Then, execute the following command:

kate@listener-host

CHATTER_ROLE=listener docker compose up --build --force-recreate

tip

You can also run the Docker-based demo on the same host, by running Husarnet within the container:

👉 See the full ros-discovery-server example here.