← Roblox Interview Insights

Roblox·Software Engineer·Onsite - System Design / Architecture·Senior

Senior
Jun 2026

Summary

Roblox system design round focused on an audio detection system, and the metrics/evaluation portion was way more involved than I expected. Less about architecture and more about how you'd actually know if the thing was working.

Questions Asked (3)

Q1

How would you define and monitor success for an audio detection system, covering both product metrics like precision/recall and per-class error rates, and system metrics like latency, throughput, and cost per hour of audio?

Product Analytics & MetricsSystem DesignTechnical Trade-offs
Author's notes

This sprawled fast.

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AI HintsAI Generated

Suggested Approach

Start by defining success in terms of both product and system metrics, then explain how you would monitor them in production. Emphasize the trade-offs between precision/recall and latency/cost, and how you would balance them based on business goals.

Pro tip: Tie metrics to business impact—e.g., false positives may annoy users while false negatives may miss critical events—and propose a tiered alerting system to avoid alert fatigue.

1. Define Product Metrics

Identify key product metrics such as precision, recall, F1-score, and per-class error rates. Explain how these align with user experience and business objectives.

2. Define System Metrics

Outline system-level metrics including latency (p50, p95, p99), throughput (audio hours processed per second), and cost per hour of audio. Discuss how these impact scalability and operational efficiency.

3. Establish Monitoring Infrastructure

Describe how to collect and visualize metrics using tools like Prometheus, Grafana, or custom dashboards. Include logging and tracing for debugging.

4. Set Alerts and Thresholds

Define alerting rules based on deviations from expected metric ranges. Prioritize alerts by severity and business impact to avoid noise.

5. Iterate and Optimize

Explain how you would use monitoring data to identify bottlenecks, retrain models, and optimize system performance over time.

Key Points to Mention

  • Precision, recall, F1-score, and per-class error rates for product metrics
  • Latency percentiles (p50, p95, p99), throughput, and cost per hour of audio for system metrics
  • Trade-offs between model accuracy and system efficiency (e.g., larger models may improve precision but increase latency and cost)
  • Monitoring tools and practices (e.g., Prometheus, Grafana, logging, tracing)
  • Alerting strategies and threshold setting to balance sensitivity and specificity
  • Continuous improvement through A/B testing, model retraining, and infrastructure optimization

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q2

Walk me through how you'd set alert thresholds and design dashboards for this kind of ML-powered system, and what signals would actually tell you something is going wrong before users notice.

Product Analytics & MetricsSystem Design
Author's notes

Went okay.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the ML system's purpose and user impact, then structure your answer around a layered monitoring strategy: model health, system performance, and business outcomes. Emphasize leading indicators and proactive alerting, and describe how you'd design dashboards for different audiences (engineers, product, executives).

Pro tip: Tie every metric to a user-facing outcome and set thresholds based on historical baselines and acceptable error budgets, not arbitrary numbers. This shows you understand both engineering and product priorities.

1. Define objectives and user impact

Clarify what the ML system does, its key user journeys, and what 'going wrong' means for users. Identify the critical metrics that directly reflect user experience.

2. Identify leading and lagging signals

List signals across data quality, model performance, system health, and business KPIs. Prioritize leading indicators that can predict issues before users are affected.

3. Set thresholds and alerting policies

Establish thresholds using historical baselines, statistical process control, or error budgets. Define alert severity, routing, and escalation based on impact and urgency.

4. Design dashboards for different audiences

Create role-specific dashboards: real-time operational views for engineers, trend and cohort analyses for product managers, and high-level health summaries for leadership.

5. Iterate and close the loop

Regularly review alert effectiveness and dashboard usage, incorporate feedback, and adjust thresholds and metrics as the system evolves.

Key Points to Mention

  • Data drift and model drift detection (e.g., input feature distributions, prediction distributions)
  • System performance metrics: latency, throughput, error rates, resource utilization
  • Business metrics: user engagement, conversion, retention, and their correlation with model outputs
  • Alerting best practices: avoid alert fatigue, use multi-window thresholds, and include runbooks
  • Dashboard design principles: clarity, drill-down capability, and real-time vs. historical views
  • Feedback loops: A/B testing, canary deployments, and shadow mode for safe rollouts

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q3

How would you safely roll out a new model or updated detection threshold, including shadow evaluations and A/B testing strategies before full deployment?

A/B Testing & ExperimentationSystem DesignTechnical Trade-offs
Author's notes

Shadow mode was the first thing I said and that landed well.

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AI HintsAI Generated

Suggested Approach

Start by emphasizing a phased rollout that begins with offline validation and shadow evaluation to catch regressions without user impact. Then describe a controlled A/B test with clear success metrics, guardrail metrics, and statistical rigor before gradually ramping up to full deployment. Highlight the importance of monitoring, rollback plans, and iterative learning.

Pro tip: Frame your answer around risk mitigation and data-driven decision-making: show that you treat model rollouts like any other production change, with canary releases, automated rollbacks, and a clear definition of success. Mention that you'd align with product and data science teams early to define metrics and avoid p-hacking.

1. Offline Validation & Shadow Evaluation

Evaluate the new model or threshold on historical data and run it in shadow mode alongside the current system to compare outputs without affecting users. This catches obvious regressions and provides initial confidence.

2. Define Success & Guardrail Metrics

Work with stakeholders to establish primary success metrics (e.g., engagement, revenue) and guardrail metrics (e.g., latency, error rates, safety violations). Set minimum detectable effect and required sample size.

3. Design and Run A/B Test

Randomly assign a small percentage of users to the new model (treatment) and the rest to the current model (control). Ensure proper randomization, avoid interference, and monitor metrics in real-time with statistical tests.

4. Gradual Ramp & Monitoring

If the A/B test shows positive results without guardrail violations, gradually increase the treatment percentage (e.g., 1% → 5% → 20% → 50% → 100%). Continuously monitor for anomalies and be ready to roll back.

5. Post-Deployment Review & Iteration

After full rollout, conduct a post-mortem to document learnings, monitor long-term effects, and plan for future iterations. Ensure the system remains healthy and the model performs as expected.

Key Points to Mention

  • Shadow mode: running new model in parallel without user impact to compare predictions.
  • A/B testing best practices: randomization, control group, statistical significance, and avoiding peeking.
  • Guardrail metrics: latency, error rates, safety, and business metrics to prevent negative side effects.
  • Gradual rollout: canary releases and percentage-based ramps to limit blast radius.
  • Rollback strategy: automated alerts and ability to revert quickly if issues arise.
  • Cross-functional collaboration: aligning with data science, product, and infra teams on metrics and deployment plan.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.