Merely "use the network to make calls between them instead of being local" will add 10 times the complexity -- you suddenly have a distributed system, latency, delays, parts that can be on or off, de-centralized configuration (which can also get out of sync), and so on.

meaning that you get to throw network and server errors into the mix of things that can go wrong, and you get the fun of tracing failures back 3 hops to a server that decides to take too long to run a process one day and times out a connection downstream.

it's horrible debugging stuff like this.