Real-World Reliability Engineering Lessons

Introduction

Reliability engineering lessons are earned through incidents, failed rollouts, and repeated feedback from customers. The most durable lessons focus on guardrails and repeatable practices rather than heroic debugging.

Lesson 1: SLOs Must Drive Priorities

Treat SLOs as a product requirement. If the error budget is exhausted, feature velocity should slow until reliability is restored.

Lesson 2: Limit Blast Radius by Default

Use canary releases, feature flags, and progressive rollouts. The smaller the blast radius, the easier it is to recover without customer impact.

Lesson 3: Automate Recovery Paths

Automated rollback and circuit breakers reduce mean time to mitigation. The following example implements a minimal circuit breaker in Node.js for unstable dependencies.

export class CircuitBreaker {
  constructor(failureThreshold, resetAfterMs) {
    this.failureThreshold = failureThreshold;
    this.resetAfterMs = resetAfterMs;
    this.failures = 0;
    this.openedAt = null;
  }

  async execute(operation) {
    if (this.openedAt && Date.now() - this.openedAt < this.resetAfterMs) {
      throw new Error("circuit.open");
    }

    try {
      const result = await operation();
      this.failures = 0;
      this.openedAt = null;
      return result;
    } catch (error) {
      this.failures += 1;
      if (this.failures >= this.failureThreshold) {
        this.openedAt = Date.now();
      }
      throw error;
    }
  }
}

Lesson 4: Postmortems Must Create Work

Every major incident should result in tracked, prioritized action items. The action items should be reviewed for completion, not just written down.

Conclusion

Reliability engineering is a practice of disciplined guardrails, objective signals, and continuous learning. The lessons above translate directly into lower incident rates and faster recovery.