Circuit breaker pattern in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the Circuit Breaker States

Which of the following correctly describes the three main states of a circuit breaker in system design?

A Closed: Requests flow normally; Open: Requests are blocked; Half-Open: Some requests allowed to test recovery

B Closed: Requests are blocked; Open: Requests flow normally; Half-Open: All requests are retried

C Closed: System is down; Open: System is up; Half-Open: System is restarting

D Closed: Requests are queued; Open: Requests are dropped; Half-Open: Requests are duplicated

💡 Hint

Think about how a circuit breaker protects a system from failures by controlling request flow.

The circuit breaker has three states: Closed means requests pass through normally. Open means requests are blocked to prevent further failures. Half-Open allows limited requests to check if the system has recovered.

❓ Architecture

intermediate

Placing a Circuit Breaker in a Microservices Architecture

Where is the best place to implement a circuit breaker in a microservices architecture to protect a service from downstream failures?

A On the database server

B Inside the downstream service itself

C On the client side before calling the downstream service

D On the network firewall

💡 Hint

Consider where you want to stop requests before they reach a failing service.

The circuit breaker is typically placed on the client side to stop requests from reaching a failing downstream service, preventing cascading failures.

❓ scaling

advanced

Scaling Circuit Breaker for High Traffic Systems

In a high traffic distributed system, what is a key challenge when scaling circuit breakers across multiple instances, and how can it be addressed?

A Challenge: Too many retries; Solution: Disable retries globally

B Challenge: Increased latency; Solution: Remove circuit breakers entirely

C Challenge: Overloading the database; Solution: Cache all requests

D Challenge: Inconsistent state across instances; Solution: Use centralized state storage or distributed consensus

💡 Hint

Think about how multiple instances share information about failures.

When multiple instances have their own circuit breakers, their states may differ causing inconsistent behavior. Using centralized storage or distributed consensus helps keep states synchronized.

❓ tradeoff

advanced

Tradeoffs of Circuit Breaker Timeout Settings

What is a tradeoff when setting a very short timeout duration for the circuit breaker before it transitions from Open to Half-Open?

A May cause premature retries leading to repeated failures

B Increases system downtime by blocking requests too long

C Reduces system responsiveness by allowing too many requests

D Causes the circuit breaker to never open

💡 Hint

Consider what happens if the system tries to recover too quickly.

A short timeout means the circuit breaker tests the service too soon, possibly before it has recovered, causing repeated failures and instability.

❓ estimation

expert

Estimating Capacity for Circuit Breaker State Storage

You have 1000 microservice instances each with 10 downstream services protected by circuit breakers. Each circuit breaker state requires 1KB of memory. Estimate the total memory needed to store all circuit breaker states if centralized storage is used.

A Approximately 1 MB

B Approximately 10 MB

C Approximately 100 MB

D Approximately 1 GB

💡 Hint

Multiply instances by services and memory per state.

Total states = 1000 instances * 10 services = 10,000 states.
Memory = 10,000 * 1KB = 10,000 KB = ~10 MB.