fastdds-discovery-server-demo

Using Fast DDS Discovery Server with multiple hosts connected over the Internet with Husarnet p2p VPN.

Intro

According to the docs: the Fast DDS Discovery Server protocol is a feature that offers a centralized dynamic discovery mechanism, as opposed to the distributed mechanism used in DDS by default.

This feature is especially important for ROS 2 devices that are not connected to the same WiFi router, and thus multicasting (used for a standard DDS discovery) is not efficient enough, not convenient or even is not possible.

This repo presents how to use FastDDS Discovery Server in a ROS 2 talker/listener demo. Each device can be in different network, and public IP is not required.

The Discovery Server is used only during a service discovery phase. The actual messages are forwarded with minimal latency between devices thanks to Husarnet peer-to-peer VPN.

Get your Husarnet Join Code

Before running examples get your Husarnet Join Code. You will use it to connect Docker containers to the same VPN network.

At first rename .env.template file to .env.

You will find your Join Code at https://app.husarnet.com
-> Click on the desired network
-> Add element button
-> Join code tab

…and change the HUSARNET_JOINCODE variable in the .env files.

Get the ros:galactic image with Fast DDS v2.4.0

Fast DDS is not a default RMW in ROS 2 Galactic. Also hostnames for DDS Discovery Server in Fast DDS .xml files are not supported in versions < v2.4.0 that are available in the package repository (installed with apt-get install ros-${ROS_DISTRO}-rmw-fastrtps-cpp).

This is why we need to build a new Docker Image based on ros:galactic with Fast DDS v2.4.0 built from source.

Docker registry (ARM64 and AMD64)

Building Fast DDS v2.4.0 from source takes a while (especially for ARM64) so you can use a prebuild image from this repo:

docker pull ghcr.io/dominikn/ros-galactic-fastdds:v2.4.0

Local build

The Docker image is built from this repo: https://github.com/DominikN/ros-galactic-fastdds.

Deployment

Prepare 3 devices (eg. laptop, Raspberry Pi etc.) with Docker and Docker-Compose installed. They could be in the same, or in different Ethernet/WiFi/LTE networks.

💡 Tip

You can also run those 3 Docker Compose deployments on one laptop if you don't want to test it over the Internet

In this demo we will deploy different docker.compose.yml files on different devices:

• DDS Discovery Server launched by docker-compose.discovery-server.yml
• Listener (from demo-nodes-cpp ROS 2 package) launched by docker-compose.listener.yml
• Talker (from demo-nodes-cpp ROS 2 package) launched by docker-compose.talker.yml

DDS Discovery Server

docker compose -f compose.discovery-server.yaml up

Listener

docker compose -f compose.listener.yaml up

Talker

docker compose -f compose.talker.yaml up

Result

Eg. log from a listener deployment:

Status: Downloaded newer image for ghcr.io/dominikn/ros-galactic-fastdds:v2.4.0
Creating fastdds-discovery-server-demo_husarnet-listener_1 ... done
Creating fastdds-discovery-server-demo_listener_1          ... done
Attaching to fastdds-discovery-server-demo_husarnet-listener_1, fastdds-discovery-server-demo_listener_1
husarnet-listener_1  | [step 1/3] Waiting for Husarnet daemon to start
husarnet-listener_1  | ...
husarnet-listener_1  | done
husarnet-listener_1  | 
husarnet-listener_1  | [step 2/3] Waiting for Base Server connection
husarnet-listener_1  | ...
listener_1           | Waiting for "dds-discovery-server" host to be available in /etc/hosts
husarnet-listener_1  | ...
husarnet-listener_1  | ...
husarnet-listener_1  | done
husarnet-listener_1  | 
husarnet-listener_1  | [step 3/3] Joining to Husarnet network
husarnet-listener_1  | [85082] joining...
husarnet-listener_1  | [87083] joining...
husarnet-listener_1  | [89083] done.
husarnet-listener_1  | Husarnet IP address: fc94:2c41:e14f:842b:c456:8ab6:915d:2866
listener_1           | "dds-discovery-server" present in /etc/hosts:
listener_1           | fc94:acec:4daf:30b6:f28b:1f9a:f683:0638 dds-discovery-server # managed by Husarnet
listener_1           | Ready to launch ROS 2 nodes
listener_1           | [INFO] [1639528088.384928610] [listener]: I heard: [Hello World: 2]
listener_1           | [INFO] [1639528089.385449769] [listener]: I heard: [Hello World: 3]
listener_1           | [INFO] [1639528090.384367537] [listener]: I heard: [Hello World: 4]