How to set sub-process execute on the same engine as it's parent model

1. You can read about the engines in the Appian product in here:

https://docs.appian.com/suite/help/22.3/Enterprise_Architecture_Overview.html#appian-engines

2. You can compare ways to start a process, including engine usage, here:
https://docs.appian.com/suite/help/22.3/Ways_to_Start_a_Process_From_a_Process.html#comparing-ways-to-start-a-process-from-a-process

The more you design to divide load over different engines, the more scalable your solution is (as in, if you add engine instances more load could be handled).

Hope it helps out!

AFAIK this is the default behavior and, in fact, not avoidable unless you take special steps to try to avoid it (i.e. using the Start Process node instead of subprocess).

Is there any particular reason you need this behavior?  In most circumstances this is supposed to be transparent to users and even designers, except when doing planning and/or testing for heavy environmental loads.

Agree with the others, I've never seen a use case where a sub process needs to be run on the same engine - the benefit is at the server level when processes are spread over different engines for performance, server health, and there are no development or design limitations based on which engines the processes are running on.