How to Launch Multiple Nodes in One Command

Ark Launcher files are YAML-based configuration files used to launch and orchestrate multiple nodes in the Ark robotics framework. Think of them as simple startup scripts that define which nodes to run, how they connect, and what configurations to apply — all in one place.

They are similar to launch files in ROS but are cleaner, Pythonic, and much easier to modify and extend.

What Do Ark Launcher Files Do?

Define a set of nodes (e.g. robot control, camera stream, simulator, etc.)
Specify which Python module and class to load for each node
Load node-specific YAML configuration files

Example: Minimal Ark Launcher File

Here's a simple Ark launcher file that starts two nodes: a talker and a listener.

talker:
  target: /nfs/rlteam/sarthakdas/arkframework/examples/basics/talker_listener/talker.py
  display: terminal

listener:
  target: /nfs/rlteam/sarthakdas/arkframework/examples/basics/talker_listener/listener.py
  display: logfile

What This Does:

talker: Runs the specified Python script and shows its output in a new terminal.
listener: Runs another script and writes its output to a log file instead of the terminal.

Key Fields Explained:

target: Full path to the Python file that defines the node. Ark will run this script as a process.
display:
- terminal: Shows output live in a separate terminal window.
- logfile: Redirects output to a log file inside the logs/ directory (timestamped per run).

How to Run This Launcher

Save the above YAML to a file, e.g. launch/talker_listener.yaml, and run:

ark launch launch/talker_listener.yaml

Ark will:

Start the talker.py script in a new terminal.
Start the listener.py script silently in the background, logging to a file.
Handle lifecycle, logs, and cleanup automatically.

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