DDS-Router doesn't work once setting ROS_LOCALHOST_ONLY in Humble

[Barry-Xu-2018]

I found DDS-Router doesn't work once setting ROS_LOCALHOST_ONLY in Humble.

Test environment:
On terminal 1, run talker:

# source /opt/ros/humble/setup.bash
# export ROS_LOCALHOST_ONLY=1
# ROS_DOMAIN_ID=0 ros2 run demo_nodes_cpp talker

On terminal 2, run listener:

# source /opt/ros/humble/setup.bash
# export ROS_LOCALHOST_ONLY=1
# ROS_DOMAIN_ID=1 ros2 run demo_nodes_cpp listener

On terminal 3, run dds-router:

# cat ros2_router/route_local.yaml
##################################
# CONFIGURATION VERSION
version: v4.0


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

  - name: ROS_2_Domain_0
    kind: local
    domain: 0

  - name: ROS_2_Domain_1
    kind: local
    domain: 1

# ddsrouter --config-path /root/ros2_router/route_local.yaml 

If I unset ROS_LOCALHOST_ONLY in terminal 1 and terminal 2, listener can receive messages from talker.

In ros2, if ROS_LOCALHOST_ONLY is enable, it will do
https://github.com/ros2/rmw_fastrtps/blob/37f7ef88fbec216d47883763f185bd39fc50b5a1/rmw_fastrtps_shared_cpp/src/participant.cpp#L165-L177

  if (localhost_only) {
    // In order to use the interface white list, we need to disable the default transport config
    domainParticipantQos.transport().use_builtin_transports = false;


    // Add a UDPv4 transport with only localhost enabled
    auto udp_transport = std::make_shared<eprosima::fastdds::rtps::UDPv4TransportDescriptor>();
    udp_transport->interfaceWhiteList.emplace_back("127.0.0.1");
    domainParticipantQos.transport().user_transports.push_back(udp_transport);


    // Add SHM transport if available
    auto shm_transport = std::make_shared<eprosima::fastdds::rtps::SharedMemTransportDescriptor>();
    domainParticipantQos.transport().user_transports.push_back(shm_transport);
  }

About transport, does the DDS-Router have any special configuration for this case ?

[juanlofer-eprosima]

Hi @Barry-Xu-2018 , which version of DDS-Router are you using? And against which Fast-DDS version did you build? Are the three processes run in the same Docker container?

[Barry-Xu-2018]

@juanlofer-eprosima

DDS-Router is v2.1.0 and Fast-DDS is v2.13.1.

Are the three processes run in the same Docker container?

Yes.

[juanlofer-eprosima]

Hi @Barry-Xu-2018 , this is a known problem affecting older Fast-DDS versions (including v2.6 present in Humble). The explanation and fix was introduced here. If willing to enforce localhost communication in this case you would need to also add a whitelist to your local router participants, as shown here, i.e.:

# CONFIGURATION VERSION
version: v4.0


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

  - name: ROS_2_Domain_0
    kind: local
    domain: 0
    whitelist-interfaces:
      - "127.0.0.1"

  - name: ROS_2_Domain_1
    kind: local
    domain: 1
    whitelist-interfaces:
      - "127.0.0.1"

[Barry-Xu-2018]

Hi @juanlofer-eprosima,

Thank you for your guidance.