IEC consists of different node types. Only the process node type can be scaled horizontally, that is, there can be several instances of the process node. The different instances do not need to be located on the same host. The CPU load and the thread load can be placed on different machines for better performance..
There is no straightforward formula for when it is more beneficial to instantiate a new node versus increasing the number of processing threads. Internal tests have indicated that when the number of worker threads reach 60, it is preferable to start considering instantiating a new node. The number varies greatly given the underlying hardware and message types.