first_package에서 launch 디렉토리를 생성합니다.

launch 디렉토리 안에서 first.launch.py 파일을 생성합니다.

first.launch.py

from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
    return LaunchDescription(
        [
            Node(namespace= "turtlesim", package='turtlesim',
             xecutable='turtlesim_node', output='screen'),
            Node(namespace= "pub_cmd_vel", package='first_package',
            executable='my_publisher', output='screen'),
        ]
    )

setup.py

from setuptools import setup
import os # 추가
import glob # 추가

package_name = 'first_package'

setup(
    name=package_name,
    version='0.0.0',
    packages=[package_name],
    data_files=[
        ('share/ament_index/resource_index/packages',
            ['resource/' + package_name]),
        ('share/' + package_name, ['package.xml']),
				#추가
        ('share/' + package_name + '/launch', glob.glob(os.path.join('launch','*.launch.py')))
    ],

Build 및 실행

colcon build --packages-select first_package

ros2 launch first_package first.launch.py