microservice.py

from __future__ import print_function
import time
import random
from functools import wraps

def microservice(f):
    @wraps(f)
    def wrapper(*args, **kwargs):
        # Network connections require RAM,
        x = list(range(1000))

        # and CPU overhead.
        for _ in x:
            _ = 42 * x

        # Networks are slow. Sometimes *really* slow.
        time.sleep(random.expovariate(10))
        if random.randint(1, 100) == 1:
            time.sleep(900)

        # Networks are unpredictible.
        choices = []

        # Sometimes everything works.
        def run():
            return f(*args, **kwargs)
        choices.append(run)

        # Sometimes, they work even though it looks like they didn't.
        def run():
            f(*args, **kwargs)
            while True:
                time.sleep(300)
        choices.append(run)

        # Sometimes, the service at the other end has changed and it no longer
        # does what you expect..
        def run():
            return g(*args, **kwargs)
        choices.append(run)

        # For some protocols, your message can be delivered more than once.
        def run():
            f(*args, **kwargs)
            f(*args, **kwargs)
            f(*args, **kwargs)
            return f(*args, **kwargs)
        choices.append(run)

        # You can run out of TCP ports, file descriptiors, or exhaust any
        # number of other resources.
        def run():
            raise OSError
        choices.append(run)

        # Network failures can mean failures never get reported to you,
        def run():
            try:
                return f(*args, **kwargs)
            except:
                return None
        choices.append(run)

        # but when the failures do make it back, they are usually pretty opaque.
        def run():
            try:
                return f(*args, **kwargs)
            except:
                return Exception(500)
        choices.append(run)

        # But you never know which of these things will happen!
        return random.choice(choices)()

    return wrapper

# But if you have a good reason, a service can still be a net win.

@microservice
def message():
    return "hello microservice world!"

# Have fun!

if __name__ == '__main__':
    print(message())