Architecture Intermediate

Circuit Breaker Pattern — Protection Against Cascading Failures¶

Circuit BreakerResiliencePatterns 3 min read

Implementing the Circuit Breaker pattern for resilient microservices. States, configuration, and practical examples.

The Cascading Failure Problem¶

When service B stops responding, service A waits for a timeout. Requests pile up and failure spreads through the entire system. Circuit Breaker fails fast instead of waiting.

Three States¶

• Closed — normal operation, counts error rate
• Open — requests are immediately rejected
• Half-Open — allows test requests through

class CircuitBreaker {
    constructor(opts = {}) {
        this.threshold = opts.failureThreshold || 5;
        this.resetTimeout = opts.resetTimeout || 30000;
        this.state = 'CLOSED';
        this.failures = 0;
        this.lastFailure = null;
    }
    async call(fn) {
        if (this.state === 'OPEN') {
            if (Date.now() - this.lastFailure > this.resetTimeout)
                this.state = 'HALF_OPEN';
            else throw new Error('Circuit OPEN');
        }
        try {
            const result = await fn();
            this.failures = 0; this.state = 'CLOSED';
            return result;
        } catch (e) {
            this.failures++;
            this.lastFailure = Date.now();
            if (this.failures >= this.threshold) this.state = 'OPEN';
            throw e;
        }
    }
}

Libraries¶

• Node.js: opossum
• Java: Resilience4j
• Python: pybreaker
• .NET: Polly

Summary¶

Circuit Breaker is a must-have in distributed architecture. Always combine with fallback logic and monitoring.

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