Explain the principles of remote procedure calls (RPC) and their role in distributed systems.

Remote Procedure Calls (RPC) allow a program to invoke a function or method that executes on another computer in the network as if it were a local call.

Working principle:

• The client calls a remote procedure, passing the necessary parameters.
• The request is serialized and sent over the network to the server.
• The server deserializes the request, executes the procedure, and serializes the result.
• The client receives the response and continues its work.

In distributed systems, RPC simplifies interaction between components, hiding network details and enabling the construction of modular, scalable applications.

Example in Python using the xmlrpc library:

from xmlrpc.server import SimpleXMLRPCServer

def add(x, y):
    return x + y

server = SimpleXMLRPCServer(('localhost', 9000))
server.register_function(add, 'add')
server.serve_forever()

The client can call the add function remotely as if it were a regular method.