Example of how server and load balancer work. Balancing algorithm uses Round Robin algorithm.

loadbalancer_example.py

from typing import Sequence

class Request:
    def __init__(self, id):
        self.id = str(id)

    def __str__(self):
        return '[Request: %s]' % self.id

class Response:
    def __init__(self, id):
        self.id = id

    def __str__(self):
        return '[Response: %s]' % self.id


class Server:
    def __str__(self):
        return '[Server: %s]' % self.name

    def process(self, request: Request) -> Response:
        raise NotImplementedError('process need to implement')

class ImageServer(Server):
    def __init__(self, name: str):
        self.name = name

    def process(self, request: Request) -> Response:
        return Response('image' + request.id)


class MsgServer(Server):
    def __init__(self, name: str):
        self.name = name

    def process(self, request: Request) -> Response:
        return Response('msg' + request.id)


class LoadBalancer:
    def __init__(self, servers: Sequence[Server]=[]):
        self.server_manager = []
        self.request_counts = 0

    def register(self, server: Server) -> None:
        self.server_manager.append(server)

    def unregister(self, server: Server) -> None:
        for i, mserver in enumerate(self.server_manager):
            if mserver is server:
                break
        self.server_manager.pop(i)

    def log(self, request: Request, response: Response):
        print(request, ' : ', response)

    def dispatch(self, request: Request) -> Response:
        '''
        round robin algorithm
        '''
        self.request_counts += 1
        n = len(self.server_manager)
        server = self.server_manager[self.request_counts % n]
        response = server.process(request)
        self.log(request, response)
        return response



if __name__ == '__main__':
    servers = [ImageServer('a'), MsgServer('b')]
    lb = LoadBalancer()
    for s in servers:
        lb.register(s)

    for request in map(Request, range(10)):
        lb.dispatch(request)

"""
[Request: 0]  :  [Response: msg0]
[Request: 1]  :  [Response: image1]
[Request: 2]  :  [Response: msg2]
[Request: 3]  :  [Response: image3]
[Request: 4]  :  [Response: msg4]
[Request: 5]  :  [Response: image5]
[Request: 6]  :  [Response: msg6]
[Request: 7]  :  [Response: image7]
[Request: 8]  :  [Response: msg8]
[Request: 9]  :  [Response: image9]
"""