API connection “retry logic with a cooldown period” simulator ( Python exercise )

This is a very simple API call “circuit-breaker” style simulator I’ve written in Python. But since it’s a stateless code snippet, you should call it most likely a “retry logic with a cooldown period” simulator. But there are valid use case scenarios when stateless is the desired state type. For example when a validation of a dataset against a service can either pass or fail and throw an exception and cause the execution flow to halt. This is typical for data-flow styled apps. In such case the circuit-open state is not acceptable. Anyway the goal is to make sure, that whenever we have a connection (or timeout) error during the API call ,we retry after 10 seconds, after 20 seconds, after 30 seconds and then quit trying. The ConnectionError exception is simulated using a non-routable address 10.255.255.1.

However in the microservices world, if you want to implement the full-scale state-full circuit-breaker, please have a look at this article.

import datetime
import time
import logging
import requests

iterator = 1
attempt = 1

# while cycle to simulate connection error using non-routable IP address
while iterator < 40:
    try:
        # if iterator inside the range to simulate success
        if 1 < iterator < 8:
            r = requests.get('https://data.police.uk/api/crimes-at-location?date=2017-02&location_id=884227')
        # else iterator outside the range to simulate the error event
        else:
            r = requests.get('http://10.255.255.1')
        if r.status_code != requests.codes.ok:
            logging.error('Wrong request status code received, %s', r.status_code)
        r = r.json()
        print(r)
        attempt = 1
    except (requests.exceptions.ConnectionError, requests.exceptions.Timeout,
            requests.exceptions.ConnectTimeout, requests.exceptions.ReadTimeout) as conn_err:
        print(f'bingo, ConnectionError, now lets wait {attempt * 10} seconds before retrying', (datetime.datetime.now()))
        time.sleep(attempt * 10)
        attempt = attempt + 1
        if attempt > 3:
            logging.error('Circuit-breaker forced exit')
            raise conn_err
    iterator = iterator + 1

Also try avoiding Python time.sleep() method in AWS Lambdas as this would not be cost efficient, AWS Step Functions would be much more appropriate.

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