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

Senior
Jun 2026

Summary

System design round at Headway for a software engineer role. The question was a classic 'slow server under load' scenario but they wanted you to go pretty deep across a lot of dimensions, not just say 'add more servers' and call it a day.

Questions Asked (1)

Q1

Your server is getting slow because of a sudden spike in incoming requests. How do you diagnose and fix it?

System DesignTechnical Trade-offsRoot Cause Analysis
Author's notes

I started with horizontal scaling and load balancers which was fine, but I jumped there too fast without talking about profiling first.

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AI HintsAI Generated

Suggested Approach

Start by acknowledging the symptom and outlining a systematic diagnostic process: check monitoring dashboards, logs, and system metrics to identify the bottleneck. Then propose immediate mitigations (e.g., scaling, rate limiting) and long-term fixes (e.g., caching, query optimization), emphasizing trade-offs and root cause analysis.

Pro tip: Mention the importance of having a runbook and post-mortem culture—showing you think beyond the immediate fix to prevent recurrence and improve team resilience.

1. Assess and Monitor

Check monitoring tools (e.g., Prometheus, Datadog) for CPU, memory, I/O, and network metrics; review logs for errors or slow queries to pinpoint the bottleneck.

2. Identify Root Cause

Determine if the spike is due to increased traffic, inefficient code, database contention, or external dependencies; use profiling and tracing to narrow down.

3. Apply Immediate Mitigations

Implement quick fixes like horizontal scaling, rate limiting, caching, or load shedding to restore service and buy time for deeper analysis.

4. Implement Long-Term Solutions

Address the root cause with optimizations (e.g., query tuning, code refactoring, adding caching layers) and consider architectural changes for scalability.

5. Validate and Prevent

Verify fixes with load testing, update monitoring/alerting, and conduct a post-mortem to document lessons learned and prevent future incidents.

Key Points to Mention

  • Monitoring and observability tools (metrics, logs, traces)
  • Horizontal vs vertical scaling trade-offs
  • Caching strategies (e.g., Redis, CDN)
  • Database optimization (indexing, query tuning, connection pooling)
  • Rate limiting and load shedding
  • Post-mortem and continuous improvement

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