Circuit breaker pattern in HLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of the Circuit Breaker pattern in system design?

The Circuit Breaker pattern helps prevent a system from repeatedly trying to perform an operation that is likely to fail, protecting the system from cascading failures and allowing it to recover gracefully.

beginner

Name the three main states of a Circuit Breaker.

The three main states are: <br>1. Closed - requests flow normally.<br>2. Open - requests are blocked to prevent failure.<br>3. Half-Open - a limited number of requests are allowed to test if the system has recovered.

intermediate

How does the Circuit Breaker decide to switch from Closed to Open state?

It switches to Open state when the failure rate of requests exceeds a configured threshold within a certain time window, indicating the downstream service is likely down or overloaded.

intermediate

What happens during the Half-Open state in the Circuit Breaker pattern?

During Half-Open, the system allows a limited number of test requests to pass through. If these succeed, the breaker resets to Closed. If they fail, it returns to Open to prevent further failures.

advanced

Why is the Circuit Breaker pattern important for scalability and reliability?

It prevents system overload by stopping repeated calls to failing services, reducing resource waste and allowing the system to recover faster, which improves overall reliability and scalability.

What state does a Circuit Breaker enter when it detects too many failures?

A Disabled

B Closed

C Half-Open

D Open

The Circuit Breaker enters the Open state to stop requests from going through when failures exceed the threshold.

In which state does the Circuit Breaker allow a limited number of requests to test recovery?

A Half-Open

B Open

C Idle

D Closed

Half-Open state allows some requests to check if the downstream service has recovered.

What triggers the Circuit Breaker to move from Open to Half-Open?

A Manual reset by admin

B Failure threshold is reached

C A timeout period expires

D System restart

After a timeout, the Circuit Breaker tries to test the service by moving to Half-Open.

Which of the following is NOT a benefit of using the Circuit Breaker pattern?

A Improve system responsiveness

B Automatically fix bugs in code

C Prevent cascading failures

D Reduce resource waste

Circuit Breaker does not fix bugs; it manages failures to improve system stability.

What happens if test requests fail during the Half-Open state?

A Circuit Breaker moves back to Open

B Circuit Breaker disables itself

C Circuit Breaker moves to Closed

D Circuit Breaker ignores failures

If test requests fail, the breaker returns to Open to prevent further failures.

Explain the Circuit Breaker pattern and its states using a real-life example.

Think about how a fuse protects electrical devices from damage.

Describe how the Circuit Breaker pattern improves system reliability and scalability.

Consider what happens if a service keeps failing and how Circuit Breaker helps.