The processing units of ROS2 are “nodes”. These “nodes” are connected by topics, services and actions. The resulting connections construct a computational graph. Each “node” is not necessarily a single operating system process (aka “executable” and “components”) or on different machines (keyword “ROS_DOMAIN_ID”).
Also checkout the article here (ROS1 vs ROS2).
In the given network of “nodes” may have
- one master “node” (usually ROS1), with “global parameter” or a self defined master (often ROS2 approach) have to take over the processing flow control ,
- distribute the control through the “nodes” itself via e.g., “launch files”.
Also checkout the article here.