Circuit Breaker - SDLC

 

It’s a software designs best practice to avoid cascading failures when an application cannot process the request or fails for some reason.

Let’s say service A calls Service B. When service B has issues, can calling service like A will get 5xx errors and this can have cascading effects on the service which invoked A.

To avoid this issue, it’s good to have a circuit break pattern.

When a service fails continuously for 3 times  then we have open the “Circuit Breaker”, 

• Service B will no longer accept requests from service A.

• Service B handles the request by queueing them to process later once service B is recovered.

• It can fail over the request to some other service.

• It can half open after certain amount of time to see if the service recovered.

Simple Python Program Implementing Circuit Breaker:

The program uses random.random function to generate numbers between 0.0 to 1.0.

If the generated number is lesser than 0.5 for 3 times, its calls another function as part of circuit breaker (queue_service).

In this service, we are adding a sleep logic for 10 sec and try processing the request.

import random
import time
from datetime import datetime
def working_service():
    if random.random() < 0.5:
        print(f"Request Completed - {datetime.now()}")
    else:
        raise Exception("Request Could Not Be Completed.")

def queue_service():
    print(f"Circuit Breaker Triggered. Request Queued And It Will Be Processed Later - {datetime.now()}")
    # Recovery time
    time.sleep(10)

fail_count = 0
for i in range(10):
    try:
        working_service()
    except Exception as e:
        fail_count = fail_count + 1
        if fail_count >=3:
            queue_service()
            fail_count = 0
        else:
            print(f"Request Failed. Circuit Breaker Not Triggered - {datetime.now()}")