Why is it not possible to use site-to-site with an input port inside a process group?
I want to achieve this because we have tenants with their own process groups and they want to use the site-to-site inside the same cluster pattern to achieve the load balancing. A lot of processors must be run on the master node only and must distribute load across the whole cluster (ListFiles -> FetchFiles -> ProcessFiles -> ...).
I'm forced to create input port on the root Flow Canvas and it breaks my multi-tenancy autonomy...
The idea has always been that a port connects you to the thing above/outside of yourself, so when you are inside a process group it connects you to the parent process group, and when you are on the root canvas it connects you outside that root group to other instances.
This behavior existed well before NiFi's current multi-tenancy security model so it was not originally an issue, but you are correct that this creates a problem for letting tenants fully manage themselves.
This is something the Apache NiFi community may want to address in the future.