Circuit Breaker Pattern - Cloud Patterns

Definition

The Circuit Breaker Pattern prevents an application from repeatedly trying to execute an operation that's likely to fail. It monitors for failures and, when a threshold is reached, trips the circuit breaker to prevent further attempts. After a timeout, it allows test requests to check if the underlying issue is resolved.

When to Use It

Protecting against cascading failures in distributed systems
Calling remote services that might be unavailable
You want to fail fast instead of waiting for timeouts
Implementing graceful degradation
Providing fallback mechanisms
Systems requiring high availability

Pros & Cons

✓ Pros

Prevents cascading failures
Fail fast instead of long timeouts
Improves system stability
Automatic recovery detection
Better resource utilization
Enables graceful degradation

✗ Cons

Adds complexity to the system
Requires careful threshold tuning
May block valid requests temporarily
Monitoring overhead
State management required
Testing edge cases is complex

Architecture Diagram

Circuit Breaker States and Flow
================================

                    ┌──────────────┐
              ┌─────┤    CLOSED    ├─────┐
              │     │  (Normal)    │     │
              │     └──────┬───────┘     │
              │            │             │
    Success   │            │ Failure     │ Reset
    Count     │            │ Threshold   │ Timer
    Reset     │            ▼ Exceeded    │
              │     ┌──────────────┐     │
              │     │     OPEN     │     │
              │     │  (Blocking)  │     │
              │     └──────┬───────┘     │
              │            │             │
              │            │ Timeout     │
              │            ▼             │
              │     ┌──────────────┐     │
              └────►│ HALF-OPEN    │─────┘
                    │  (Testing)   │
                    └──────────────┘

Request Flow:
─────────────

┌──────────┐         ┌──────────────────┐         ┌──────────┐
│          │         │ Circuit Breaker  │         │ External │
│  Client  │────────►│                  │────────►│ Service  │
│          │ Request │  State: CLOSED   │ Forward │          │
└──────────┘         └──────────────────┘         └──────────┘
                              │
                              │ Track Failures
                              ▼
                     ┌─────────────────┐
                     │  Failure Count  │
                     │  Exceeds Limit? │
                     └────────┬────────┘
                              │ Yes
                              ▼
                     ┌─────────────────┐
                     │  State: OPEN    │
                     │  Return Error   │
                     │  (Fail Fast)    │
                     └────────┬────────┘
                              │ Wait Timeout
                              ▼
                     ┌─────────────────┐
                     │ State: HALF-OPEN│
                     │ Allow Test Req  │
                     └────────┬────────┘
                              │
                     ┌────────┴────────┐
                     │                 │
              Success│                 │Failure
                     ▼                 ▼
              ┌──────────┐      ┌──────────┐
              │  CLOSED  │      │   OPEN   │
              └──────────┘      └──────────┘

Configuration:
• Failure Threshold: 5 failures
• Timeout: 30 seconds
• Success Threshold: 2 successes