configure-multi-robot

name: configure-multi-robot description: Configure, name, and isolate multiple robots in AirStack. Use whenever launching multi-robot, multiple robots, swarm, or fleet scenarios; setting ROBOT_NAME; debugging cross-robot topic collisions; choosing a ROS_DOMAIN_ID; or namespacing topics, TF frames, and DDS bridges across robots. license: Apache-2.0 metadata: author: AirLab CMU repository: AirStack

Skill: Configure Multi-Robot Setup

When to Use

Reach for this skill any time you:

• Spawn more than one robot in simulation (NUM_ROBOTS > 1)
• Deploy multiple physical aircraft (VOXL, Jetson, etc.)
• Debug topic collisions, missing topics on /robot_2/..., or "two robots talking on the same topic"
• Write a new launch file or YAML config that hardcodes a topic path
• Vary --num-robots in the system test suite (tests/)
• Add a node that subscribes to or publishes a robot-specific topic
• Set up the desktop_split / offboard profile where global planning runs on a separate machine

If you only ever touch one robot, you can usually skip this skill — but the moment a second drone enters the picture, every assumption about hardcoded /drone1/... topic names becomes a bug.

Prerequisites

• Familiarity with the AirStack docker-compose layout (.env, robot/docker/, simulation/{isaac-sim,ms-airsim}/)
• Basic understanding of ROS 2 namespaces and TF frame names
• You have already read docs/robot/docker/robot_identity.md, or are willing to as you go — that file is the canonical reference for the resolution mechanism

How ROBOT_NAME Flows Through the Stack

ROBOT_NAME is not a single static value. It is computed per container at shell start by robot/docker/.bashrc and propagated into every ROS launch substitution. The full chain:

.env  (ROBOT_NAME_MAP_CONFIG_FILE, NUM_ROBOTS)
  │
  ▼
docker-compose.yaml  (ROBOT_NAME_SOURCE=container_name | hostname,
                      deploy.replicas: ${NUM_ROBOTS:-1})
  │
  ▼
robot/docker/.bashrc  (runs on container shell start)
  │
  ├─ ROBOT_NAME_SOURCE=container_name  →  resolve `hostname` back to docker container name
  │                                      (e.g. `airstack-robot-desktop-1`)
  ├─ ROBOT_NAME_SOURCE=hostname        →  use OS hostname directly (`robot-1` on real HW)
  │
  ▼
robot/docker/robot_name_map/resolve_robot_name.py
  applies regex rules from $ROBOT_NAME_MAP_CONFIG_FILE
  │
  ▼
exports ROBOT_NAME=robot_<N>     (e.g. robot_1)
        ROS_DOMAIN_ID=<N>        (e.g. 1)
  │
  ▼
ros2 launch reads $(env ROBOT_NAME) → topic remappings, push_ros_namespace,
                                       MAVROS FCU URLs, DDS allowlists, etc.

The default mapping rule in robot/docker/robot_name_map/default_robot_name_map.yaml:

- pattern: '.*robot-.*(\d+)'
  robot: 'robot_{1}'
  domain_id: '{1}'
- pattern: '.*'           # catch-all
  robot: 'unknown-robot'
  domain_id: '0'

So airstack-robot-desktop-1 → ROBOT_NAME=robot_1, ROS_DOMAIN_ID=1. Replica 2 → robot_2, domain 2. Etc. The container name is the source of truth in simulation.

The top-level autonomy_bringup/launch/robot.launch.xml then pushes this name as the root namespace for every node it spawns:

<push_ros_namespace namespace="$(env ROBOT_NAME)" />

Every layer-bringup launch file underneath inherits that namespace, and every cross-robot remap uses /$(env ROBOT_NAME)/... to reach back out to the absolute path.

Configuring a Single Robot

The default config in .env already runs one robot. You almost never need to set ROBOT_NAME directly; instead let the resolver compute it:

# .env
NUM_ROBOTS="1"
ROBOT_NAME_MAP_CONFIG_FILE="default_robot_name_map.yaml"

airstack up
docker exec airstack-robot-desktop-1 bash -c 'echo $ROBOT_NAME $ROS_DOMAIN_ID'
# robot_1 1

If you need a non-default name (custom hostname scheme on a physical robot, or you want drone_alpha instead of robot_1), write a new mapping YAML in robot/docker/robot_name_map/ and point ROBOT_NAME_MAP_CONFIG_FILE at it. Do not hardcode ROBOT_NAME=... in compose unless you know what you are doing — it bypasses the resolver and you lose ROS_DOMAIN_ID co-assignment.

For a one-off override (e.g. ad hoc debugging):

docker exec -e ROBOT_NAME=robot_5 -e ROS_DOMAIN_ID=5 -it airstack-robot-desktop-1 bash

Launching Multiple Robots

AirStack launches multiple robots as replicas of the same container, not as multiple namespaces inside one container. Look at robot/docker/docker-compose.yaml:

robot-desktop:
  ...
  deploy:
    replicas: ${NUM_ROBOTS:-1}

So NUM_ROBOTS=3 airstack up produces three robot containers (airstack-robot-desktop-1, -2, -3), each with its own ROBOT_NAME and its own ROS_DOMAIN_ID. Each container runs the full autonomy stack independently. Cross-robot communication, when needed, goes through the DDS router (see onboard_all/config/dds_router.yaml) which bridges allowlisted topics from each per-robot domain into a shared GCS domain.

NUM_ROBOTS=3 airstack up
docker ps --format '{{.Names}}' | grep robot-desktop
# airstack-robot-desktop-1
# airstack-robot-desktop-2
# airstack-robot-desktop-3

The simulator side has to spawn matching vehicles — see Sim-Side Robot Spawning.

onboard_all vs onboard_local_offboard_global

autonomy_bringup ships two layouts, selected by the role arg / AUTONOMY_ROLE env var:

The split is significant for multi-robot: with onboard_local_offboard_global, one offboard container is launched per robot (also via replicas: ${NUM_ROBOTS}), all on ROS_DOMAIN_ID=0, and each bridges into its own per-robot onboard domain via the domain bridge config in onboard_local_offboard_global/config/dds_router.yaml. See docs/robot/autonomy_modes.md for the profile matrix.

Topic and TF Namespacing

Topics

Every cross-module topic must be prefixed with /$(env ROBOT_NAME)/.... The standard topics used across the stack (also catalogued in AGENTS.md under "Standard Topic Patterns"):

Pattern in launch XML — do this in every new module:

<remap from="odometry" to="/$(env ROBOT_NAME)/odometry_conversion/odometry" />
<remap from="global_plan" to="/$(env ROBOT_NAME)/global_plan" />

In node code, subscribe/publish using relative names (e.g. odometry) and let the launch file remap. Never write self.create_subscription(..., "/drone1/odometry", ...).

TF frames

TF frames in AirStack are also namespaced under the robot, but the namespacing happens because TF in ROS 2 honors the publishing node's namespace. The top-level launch pushes $(env ROBOT_NAME) as namespace, so a node publishing base_link ends up with the resolved frame robot_1/base_link.

Standard frame names you will see (per robot):

• {robot_name}/base_link — body-fixed frame
• {robot_name}/base_link_stabilized — yaw-only-rotated body frame
• {robot_name}/odom — odometry origin
• {robot_name}/look_ahead_point_stabilized — controller look-ahead

Two static frames are shared across robots:

• world — global root
• map — global map frame, anchored at world

The static world → map broadcaster is launched once per robot inside robot.launch.xml — multiple robots publish the identical transform, which TF accepts as redundant. Do not rename map per-robot; many global planners and the GCS assume map is the shared global frame.

If you write a node that hardcodes a TF frame string, prefer relative frame IDs (base_link, odom) over absolute ones — the namespace prefix gets added automatically. If you must use an absolute name, build it from the env var:

robot_name = os.environ["ROBOT_NAME"]
self.target_frame = f"{robot_name}/base_link"

Sim-Side Robot Spawning

Both simulators read NUM_ROBOTS from the environment and spawn matching vehicles named robot_1, robot_2, … so the names line up with what the resolver assigns to robot containers.

Microsoft AirSim (legacy)

simulation/ms-airsim/config/generate_settings.py reads NUM_ROBOTS and renders settings.json.j2 into AirSim's settings.json. The Jinja loop produces one Vehicles.robot_<i> block per robot, each with its own TcpPort (4561 + i), ControlPortLocal (24541 + i), and spawn offset (Y = (i-1) * spawn_spacing):

{% for i in range(1, num_robots + 1) %}
"robot_{{ i }}": {
  "VehicleType": "PX4Multirotor",
  "TcpPort": {{ 4560 + i }},
  ...
  "Y": {{ (i - 1) * spawn_spacing }}
}
{% endfor %}

The ms-airsim container's entrypoint.sh (in simulation/ms-airsim/docker/) loops for i in $(seq 1 "$NUM_ROBOTS") to start one PX4 SITL instance per vehicle. AirSim binds them via the per-robot TCP ports.

Isaac Sim (Pegasus)

simulation/isaac-sim/launch_scripts/example_multi_px4_pegasus_launch_script.py reads NUM_ROBOTS and calls spawn_drone(i) in a loop. Each drone is created with robot_name=f"robot_{index}", vehicle_id=index, domain_id=index, and an X offset for spacing:

NUM_ROBOTS = int(os.environ.get("NUM_ROBOTS", "1"))
...
for i in range(1, NUM_ROBOTS + 1):
    spawn_drone(i)

To use the multi-drone launcher, set in .env:

ISAAC_SIM_SCRIPT_NAME="example_multi_px4_pegasus_launch_script.py"

(The default example_one_px4_pegasus_launch_script.py only spawns one.)

Test harness

The airstack_env fixture in tests/conftest.py parametrizes tests over (sim, num_robots, iteration) and sets:

env_overrides = {
    "NUM_ROBOTS": str(num_robots),
    ...
}

Tests that act on robots iterate n=1..num_robots and address them as /robot_{n}/... directly (see _takeoff_one_robot in tests/test_takeoff_hover_land.py). The test sets ROS_DOMAIN_ID=n for each per-robot subprocess (domain_id=n in ros2_exec(...)), matching what the resolver assigned inside the container. If you write a new test that talks to a robot, follow this same domain_id=n + /robot_{n}/... pattern.

CLI passthrough:

airstack test -m takeoff_hover_land --sim msairsim --num-robots 1,3 -v

Common Pitfalls

1. Hardcoding the robot name in topics

<!-- WRONG: only works for the first robot, breaks for /robot_2/... -->
<remap from="odometry" to="/drone1/odometry" />
<remap from="odometry" to="/robot_1/odometry" />

<!-- RIGHT -->
<remap from="odometry" to="/$(env ROBOT_NAME)/odometry" />

# WRONG
self.create_subscription(Odometry, "/robot_1/odometry", cb, 10)

# RIGHT (let launch remap a relative name)
self.create_subscription(Odometry, "odometry", cb, 10)

2. Forgetting allow_substs="true" on YAML param files

If your config/*.yaml references $(env ROBOT_NAME) or other substitutions, you must opt in:

<param from="$(find-pkg-share my_pkg)/config/my_pkg.yaml" allow_substs="true" />

Without allow_substs="true", the substitution string is loaded literally and the node sees frame_id: "$(env ROBOT_NAME)/base_link" instead of frame_id: "robot_1/base_link".

3. Two robots sharing one ROS_DOMAIN_ID

If two robots share a domain, every topic collides — both /robot_1/odometry publishers will be visible to both subscribers, and DDS will sometimes deliver crossed data. The default robot_name_map derives the domain from the robot index, so this only happens if you:

• Hardcode ROS_DOMAIN_ID in compose to the same value for two replicas
• Use a hostname that doesn't match any rule and falls through to the catch-all (both robots get unknown-robot, domain 0)

Always verify after starting:

for c in $(docker ps --format '{{.Names}}' | grep robot-desktop); do
  echo "$c: $(docker exec $c bash -c 'echo $ROBOT_NAME $ROS_DOMAIN_ID')"
done

4. Running multiple airstack up instances without isolating domains

Two developers on the same LAN running airstack up will see each other's robots if ROS_DOMAIN_ID happens to match. The airstack_network bridge in compose isolates the container network but DDS multicast can still leak over the host's actual network depending on the discovery config. If you are sharing a LAN, set a distinct ROBOT_NAME_MAP_CONFIG_FILE that maps to a non-overlapping domain range (e.g. one developer uses domains 1-3, another 11-13).

5. Test harness defaulting to 1 robot

tests/conftest.py defaults to --num-robots 1,3. If you wrote a test that assumes exactly one or exactly three robots, restrict the parametrization in your own test or guard with pytest.skip(...). Don't rely on the harness picking your expected count.

6. Forgetting to pass NUM_ROBOTS to the simulator container

Both Isaac Sim and AirSim read NUM_ROBOTS themselves at startup. airstack up and the test harness propagate it for you, but if you start the simulator alone (e.g. docker compose up isaac-sim), the simulator will spawn 1 drone regardless of how many robot containers you started. Always set NUM_ROBOTS at the top-level invocation, not after the simulator is already running.

7. Hardcoded TF frame base_link from outside the namespace

A node running outside the robot namespace (e.g. a GCS node, or something launched from gcs/) cannot just look up base_link — it needs the full robot_1/base_link. Build the frame name from the robot you mean to reach:

target_frame = f"{robot_name}/base_link"

8. push_ros_namespace with an absolute remap

This is a common foot-gun:

<push_ros_namespace namespace="$(env ROBOT_NAME)" />
<node ...>
  <remap from="odometry" to="/odometry" />   <!-- absolute! escapes the namespace -->
</node>

Either keep the remap relative (to="odometry") so it joins the namespace, or write the full path explicitly (to="/$(env ROBOT_NAME)/odometry").

9. Hostname doesn't match any rule on real robots

On VOXL/Jetson with ROBOT_NAME_SOURCE=hostname, the device hostname must match a rule in the mapping YAML. If hostname returns airlab-jetson-42 and your config only matches robot-N, the resolver exits non-zero and ROBOT_NAME is unset — the autonomy stack will then launch with empty namespaces and break in confusing ways. Either rename the device or extend the mapping config.

Pre-Merge Checklist

Before merging a change that touches anything robot-namespaced:

• No /drone1/... or /robot_1/... literals in any code, config, or launch file you added or modified — search with grep -rn '/robot_[0-9]\|/drone[0-9]' <changed paths>
• Every cross-module topic uses $(env ROBOT_NAME) (in launch files) or a relative name remapped at launch time (in node code)
• Every YAML config file that references $(env ...) is loaded with allow_substs="true"
• TF frames in node code are either relative (base_link, odom) or built from os.environ["ROBOT_NAME"]
• If you added a new module to a layer bringup, you tested it with NUM_ROBOTS=2 and confirmed both robots' namespaces look identical under ros2 node list
• If you added a sim launch script, it reads NUM_ROBOTS and spawns vehicles named robot_1, robot_2, … with matching vehicle_id / domain_id
• If you added a system test that addresses a robot, it loops over range(1, num_robots + 1) and uses domain_id=n in ros2_exec(...)
• DDS router allowlists in onboard_all/config/dds_router.yaml (or the split equivalent) include any new cross-domain topic your module exposes — otherwise it will not appear on the GCS
• Verified end-to-end: NUM_ROBOTS=3 airstack up, then docker exec airstack-robot-desktop-2 bash -c 'ros2 topic list | grep robot_2' shows the same topics that airstack-robot-desktop-1 shows under robot_1

Verification Commands

Quick checks while debugging:

# Confirm each container resolved a distinct (ROBOT_NAME, ROS_DOMAIN_ID)
for c in $(docker ps --format '{{.Names}}' | grep robot-desktop); do
  docker exec "$c" bash -c 'echo "$(hostname) -> ROBOT_NAME=$ROBOT_NAME ROS_DOMAIN_ID=$ROS_DOMAIN_ID"'
done

# Each robot's nodes (run on the matching domain)
docker exec -e ROS_DOMAIN_ID=1 airstack-robot-desktop-1 bash -c \
  "source /opt/ros/jazzy/setup.bash && ros2 node list"
docker exec -e ROS_DOMAIN_ID=2 airstack-robot-desktop-2 bash -c \
  "source /opt/ros/jazzy/setup.bash && ros2 node list"

# Robots talking to each other? Use the GCS domain (0) and check the router-bridged topics
docker exec airstack-gcs-1 bash -c \
  "source /opt/ros/jazzy/setup.bash && ROS_DOMAIN_ID=0 ros2 topic list | grep -E 'robot_[0-9]+'"

# TF tree for one robot
docker exec -e ROS_DOMAIN_ID=1 airstack-robot-desktop-1 bash -c \
  "source /opt/ros/jazzy/setup.bash && ros2 run tf2_tools view_frames"

References

• docs/robot/docker/robot_identity.md — canonical reference for the resolution mechanism
• docs/robot/autonomy_modes.md — profile matrix (desktop, desktop_split, voxl, l4t, offboard)
• robot/docker/robot_name_map/ — mapping YAMLs and resolve_robot_name.py
• robot/ros_ws/src/autonomy_bringup/launch/robot.launch.xml — top-level push_ros_namespace
• robot/ros_ws/src/autonomy_bringup/onboard_all/config/dds_router.yaml — cross-domain allowlist pattern
• simulation/ms-airsim/config/generate_settings.py and settings.json.j2
• simulation/isaac-sim/launch_scripts/example_multi_px4_pegasus_launch_script.py
• tests/conftest.py — airstack_env fixture and --num-robots parametrization

Related Skills

• integrate-module-into-layer — every remap in your module must use $(env ROBOT_NAME)
• write-launch-file — patterns for env substitution and namespace pushing
• test-in-simulation — multi-robot test scenarios
• debug-module — diagnosing topic/namespace issues