System Design

Circuit Breaker Pattern

System DesignResilienceMicroservices

Prevent cascading failures in distributed systems with circuit states.

Circuit Breaker States

🟢

Closed State

The default state. Requests flow freely to the external service. The circuit breaker monitors responses for errors or timeouts.

Pass-throughMonitoring

🔴

Open State

When the failure rate exceeds a threshold, the circuit trips. All requests immediately fail-fast or return a fallback, preventing cascading failures.

Fail-FastFallback

🟡

Half-Open State

After a timeout, the breaker tests the external service by allowing a limited number of requests. If they succeed, it closes; if they fail, it re-opens.

RecoveryTesting

State Transitions

How a Circuit Breaker moves between states

flowchart TD
    C[🟢 CLOSED
Normal Operation] -->|Failures > Threshold| O[🔴 OPEN
Fail Fast]
    O -->|Wait Duration Expires| H[🟡 HALF-OPEN
Test Recovery]
    H -->|Test Success| C
    H -->|Test Failure| O

    classDef closed fill:#0f3a2b,stroke:#69f0ae,stroke-width:2px,color:#fff
    classDef open fill:#4a151b,stroke:#ff5252,stroke-width:2px,color:#fff
    classDef halfopen fill:#4d2d0c,stroke:#ff9100,stroke-width:2px,color:#fff
    class C closed
    class O open
    class H halfopen

Interactive Operation Flow

Explore the pattern with step-by-step animations

Waiting...

Normal Operation (CLOSED State)

💻

Client

⚡

CLOSED

Circuit Breaker

🌍

External Service

1. Client sends request to API

2. Circuit is CLOSED, request passes through

3. Request reaches External Service

4. Service processes successfully (200 OK)

5. Response returned to Client

Client

Circuit Breaker

Target Service

Key Concepts

Tuning criteria to fit your application's needs

Failure Threshold

The percentage or absolute number of failures required to trip the circuit (e.g., 50% failure rate over a sliding window of 100 requests).

Tip: Use sliding windows (count-based or time-based) to track failures accurately.

Wait Duration (Timeout)

The time the circuit stays OPEN before entering HALF-OPEN state to test recovery.

Tip: Implement exponential backoff for the wait duration to avoid overwhelming slow-recovering services.

Fallbacks

A graceful degradation strategy when the circuit is OPEN. instead of throwing an error, return cached data or a default value.

Tip: E-commerce product recommendations can return generic 'bestsellers' if the custom recommendation service is down.

Resilience Patterns Comparison

How different patterns handle failures in distributed systems

Pattern	Complexity	Cascading Prevention	Recovery Speed	Common Implementations
Timeouts				API Gateway, Service Mesh, Code
Retries w/ Backoff				Code, Service Mesh
Circuit Breaker				Resilience4j, Istio
Rate Limiting				API Gateway, Redis

Resources

Title	Type	Link
Circuit Breaker Pattern — Microsoft Docs	web	Open
Martin Fowler - Circuit Breaker	web	Open
Resilience4j - Circuit Breaker	web	Open
System Design: Circuit Breaker	youtube	Open

Guide Contributors

ObydulSenior Software Engineer

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Init guide environment...

Circuit Breaker States

🟢

Closed State

The default state. Requests flow freely to the external service. The circuit breaker monitors responses for errors or timeouts.

Pass-throughMonitoring

🔴

Open State

When the failure rate exceeds a threshold, the circuit trips. All requests immediately fail-fast or return a fallback, preventing cascading failures.

Fail-FastFallback

🟡

Half-Open State

After a timeout, the breaker tests the external service by allowing a limited number of requests. If they succeed, it closes; if they fail, it re-opens.

RecoveryTesting

State Transitions

How a Circuit Breaker moves between states

flowchart TD
    C[🟢 CLOSED
Normal Operation] -->|Failures > Threshold| O[🔴 OPEN
Fail Fast]
    O -->|Wait Duration Expires| H[🟡 HALF-OPEN
Test Recovery]
    H -->|Test Success| C
    H -->|Test Failure| O

    classDef closed fill:#0f3a2b,stroke:#69f0ae,stroke-width:2px,color:#fff
    classDef open fill:#4a151b,stroke:#ff5252,stroke-width:2px,color:#fff
    classDef halfopen fill:#4d2d0c,stroke:#ff9100,stroke-width:2px,color:#fff
    class C closed
    class O open
    class H halfopen

Interactive Operation Flow

Explore the pattern with step-by-step animations

Waiting...

Normal Operation (CLOSED State)

💻

Client

⚡

CLOSED

Circuit Breaker

🌍

External Service

1. Client sends request to API

2. Circuit is CLOSED, request passes through

3. Request reaches External Service

4. Service processes successfully (200 OK)

5. Response returned to Client

Client

Circuit Breaker

Target Service

Key Concepts

Tuning criteria to fit your application's needs

Failure Threshold

The percentage or absolute number of failures required to trip the circuit (e.g., 50% failure rate over a sliding window of 100 requests).

Tip: Use sliding windows (count-based or time-based) to track failures accurately.

Wait Duration (Timeout)

The time the circuit stays OPEN before entering HALF-OPEN state to test recovery.

Tip: Implement exponential backoff for the wait duration to avoid overwhelming slow-recovering services.

Fallbacks

A graceful degradation strategy when the circuit is OPEN. instead of throwing an error, return cached data or a default value.

Tip: E-commerce product recommendations can return generic 'bestsellers' if the custom recommendation service is down.

Resilience Patterns Comparison

How different patterns handle failures in distributed systems

Pattern	Complexity	Cascading Prevention	Recovery Speed	Common Implementations
Timeouts				API Gateway, Service Mesh, Code
Retries w/ Backoff				Code, Service Mesh
Circuit Breaker				Resilience4j, Istio
Rate Limiting				API Gateway, Redis

Resources

Title	Type	Link
Circuit Breaker Pattern — Microsoft Docs	web	Open
Martin Fowler - Circuit Breaker	web	Open
Resilience4j - Circuit Breaker	web	Open
System Design: Circuit Breaker	youtube	Open

Guide Contributors

ObydulSenior Software Engineer