In ROS 2 Iron Irwini, we hope to improve how discovery is managed by ROS 2. In brief:

• Broadcast discovery "distance" will be controllable by the user, in terms of off, localhost-only, and subnet-only.
• Discovery static peers will be easily specified by the user, allowing specific hosts to be discovered even when broadcast discovery is off.

For the full details, please see this Discourse post.

Below are the individual PRs that make up this feature.

• [rcl] Improve handling of dynamic discovery  rcl#1023
• [rmw] Improve handling of dynamic discovery rmw#338
• [rmw_fastrtps] Improve handling of dynamic discovery rmw_fastrtps#653
• [rmw_cyclonedds] Improve handling of dynamic discovery rmw_cyclonedds#429
• [rmw_connextdds] New RMW discovery options rmw_connextdds#108
• Change automatic environment variables to new ones. ros/ros_environment#37
• Sloretz/test discovery system_tests#512

Current status - stuff that needs to be done

• Pre-RMW freeze
  • Fast-DDS ignore_participant implementation merged: [17873] DomainParticipant::ignore_participant implementation eProsima/Fast-DDS#3412
    • Not needed with @sloretz's changes to how things work in rmw_fastrtps_cpp
  • Add comments to rcl test: [rcl] Improve handling of dynamic discovery  rcl#1023 (comment)
    • [rcl] Improve handling of dynamic discovery  rcl#1023 (comment)
  • Decide where IP addresses should be validated (What does it mean for an IP to be validated?) [rcl] Improve handling of dynamic discovery  rcl#1023 (comment)
    • Not going to validate in rcl, leave to middleware, documented
  • Decide if we should keep or delete RMW_AUTOMATIC_DISCOVERY_RANGE_DEFAULT [rmw] Improve handling of dynamic discovery rmw#338 (comment)
    • @sloretz addressed this
  • Make sure all changes build on windows (checking rmw_fastrtps here: [rmw_fastrtps] Improve handling of dynamic discovery rmw_fastrtps#653 (comment))
  • Maybe make error message more informative: [rmw_cyclonedds] Improve handling of dynamic discovery rmw_cyclonedds#429 (comment)
  • Address William's feedback on rmw_connextdds PR [rmw_connextdds] New RMW discovery options rmw_connextdds#108 (review)
  • Resolve why ConnextDDS implementation not behaving as expected: [rmw_connextdds] New RMW discovery options rmw_connextdds#108 (comment)
    • @asorbini made a patch that should address this we think (thanks!)
• Post-RMW freeze
  • ROS 2 documentation about discovery options
  • ROS Iron release notes for discovery change
  • test_discovery - Add README for how to run root tests
  • test_discovery - add rosdep keys for pytest, mininet, etc.