i like to know how do you manage the subject of configuration when you have multi project

application ( many clients ) an the application composed from distributed servers .

which each server has its own configuration .

in simple words . i have core product which have configuration A Then i have clients which using the core project but which specific configuration to the client .

the result is i have Dozens versions of the configuration which leads to total mess.

what is the common way or methodologies to handle such mess ?

Thanks