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

Senior
May 2026

Summary

eBay software engineer interview that was basically one long question dressed up as several. They wanted the full picture on a service you actually owned, not just a vague story about something you touched.

Questions Asked (5)

Q1

Walk me through a service you owned end-to-end: what was the business goal, what was your specific role, and how was it architected?

System DesignTechnical Trade-offs
Author's notes

I had a good example ready but fumbled the architecture part a bit.

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AI HintsAI Generated

Suggested Approach

Choose a service you genuinely owned end-to-end, and structure your answer around the business goal, your specific contributions, and the architecture. Use a narrative arc that connects technical decisions to business outcomes, and be ready to dive deep into trade-offs and your role.

Pro tip: Quantify the business impact (e.g., latency reduction, cost savings, revenue increase) and explicitly state what you would do differently today to show growth and self-awareness.

1. Set the Context

Briefly describe the service, its purpose, and the business goal it aimed to achieve. Mention the scale and any key constraints.

2. Define Your Role

Clearly state your specific responsibilities and ownership. Highlight what you personally designed, built, or led, and how you collaborated with others.

3. Explain the Architecture

Walk through the high-level architecture, including major components, data flow, and technologies used. Focus on how the design supported the business goal.

4. Discuss Trade-offs and Decisions

Describe key technical decisions, alternatives considered, and trade-offs made (e.g., consistency vs. availability, build vs. buy). Explain why your choices were optimal.

5. Share Outcomes and Learnings

Summarize the results, including metrics and business impact. Reflect on what you learned and what you would improve if you did it again.

Key Points to Mention

  • Business goal and how it was measured (e.g., revenue, user engagement, cost reduction)
  • Your specific role and ownership boundaries (e.g., led design, implemented core component)
  • High-level architecture diagram in words: components, interactions, and data flow
  • Key technical trade-offs and why you made them (e.g., SQL vs. NoSQL, monolith vs. microservices)
  • Scalability, reliability, and performance considerations (e.g., caching, sharding, load balancing)
  • Quantifiable outcomes and lessons learned (e.g., reduced latency by X%, handled Y requests per second)

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

Q2

What was the hardest trade-off you made while building or running that service?

Technical Trade-offsAdaptability & Ambiguity
Author's notes

This is where I think I actually did okay.

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AI HintsAI Generated

Suggested Approach

Choose a trade-off that had real stakes and a clear decision point, then walk through the constraints, options, and reasoning behind your choice. Emphasize the outcome, what you learned, and how you'd approach similar trade-offs differently now.

Pro tip: Show that you understand the business context behind the trade-off—engineers who can connect technical decisions to customer or revenue impact stand out. Also, be honest about the downsides of your choice and how you mitigated them; it demonstrates maturity and self-awareness.

1. Set the context

Briefly describe the service, its scale, and the specific challenge that forced a trade-off. Keep it concise so the interviewer understands the stakes.

2. Lay out the options

Explain the competing priorities (e.g., speed vs. reliability, cost vs. performance) and the viable alternatives you considered. Show that you evaluated multiple paths.

3. Explain your decision and rationale

State which trade-off you made and why, referencing data, user impact, or business goals. Highlight any constraints like deadlines or team capacity.

4. Describe the outcome and mitigation

Share the results—both positive and negative—and how you addressed any downsides. Quantify impact if possible (e.g., latency reduced by X%, cost increased by Y%).

5. Reflect and generalize

Summarize what you learned and how it changed your approach to similar decisions. Connect it to broader engineering principles or eBay's context.

Key Points to Mention

  • The specific technical constraints (e.g., latency, scalability, budget) that drove the trade-off
  • The alternatives you considered and why you rejected them
  • How you involved stakeholders or used data to make the decision
  • The short-term and long-term consequences of your choice
  • Any technical debt or follow-up work that resulted, and how you managed it
  • What you would do differently next time, showing growth and adaptability

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

Q3

Tell me about a significant incident on that service: what happened, what did you do, and what was the outcome?

Root Cause AnalysisAdaptability & Ambiguity
Author's notes

Blanked for a second because my best incident story is from a different service than the one I'd been talking about.

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AI HintsAI Generated

Suggested Approach

Use the STAR method to structure your answer, focusing on a specific incident where you took ownership. Highlight your technical troubleshooting, root cause analysis, and the impact of your actions on the service and the team.

Pro tip: Emphasize the lessons learned and any preventive measures you implemented to avoid similar incidents, showing a proactive mindset and maturity.

1. Set the Context

Briefly describe the service, its importance, and the incident's impact (e.g., downtime, degraded performance).

2. Explain the Incident

Detail what happened, including symptoms, when it was detected, and how it was reported.

3. Describe Your Actions

Outline the steps you took to diagnose and mitigate the issue, including tools used and collaboration with others.

4. Highlight the Root Cause

Explain how you identified the underlying cause, using techniques like log analysis, debugging, or code review.

5. Share the Outcome and Learnings

Discuss the resolution, any metrics (e.g., time to recovery), and what you changed to prevent recurrence.

Key Points to Mention

  • Specific monitoring or alerting tools used (e.g., Prometheus, Grafana, Splunk)
  • Collaboration with cross-functional teams (e.g., SRE, product managers)
  • Quantifiable impact (e.g., reduced downtime by X%, improved latency)
  • Root cause analysis techniques (e.g., 5 Whys, fishbone diagram)
  • Preventive measures implemented (e.g., automated tests, runbooks, alerts)
  • Personal accountability and ownership of the incident

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

Q4

How did you measure the impact of that service?

Product Analytics & Metrics
Author's notes

Shorter exchange than I expected.

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AI HintsAI Generated

Suggested Approach

Start by defining the specific service and its intended impact, then explain how you selected metrics that aligned with business goals. Describe the measurement methods, data sources, and how you analyzed the results to quantify impact, including any challenges and how you addressed them.

Pro tip: Tie your metrics to eBay's key business drivers like conversion rate, buyer retention, or seller engagement, and mention how you validated that changes were due to your service rather than external factors.

1. Define the service and its goal

Briefly describe the service and the specific problem it aimed to solve, clarifying the intended impact on users or the business.

2. Select relevant metrics

Explain which metrics you chose (e.g., latency, error rate, conversion, engagement) and why they were the right indicators of success.

3. Describe measurement methods

Detail how you collected data (e.g., logging, A/B testing, dashboards) and any tools or techniques used to ensure accuracy.

4. Analyze and interpret results

Discuss how you analyzed the data to quantify impact, including before/after comparisons or statistical significance, and how you isolated the service's effect.

5. Summarize impact and learnings

Conclude with the quantified impact (e.g., 'reduced latency by 30%') and any insights or follow-up actions taken.

Key Points to Mention

  • Alignment of metrics with business goals (e.g., revenue, conversion, retention)
  • Use of A/B testing or control groups to establish causality
  • Data collection tools and instrumentation (e.g., logging, monitoring, analytics platforms)
  • Quantitative results with specific numbers and percentages
  • Handling of confounding factors or limitations in measurement
  • Iterative improvement based on metrics (e.g., feedback loops)

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

Q5

Looking back, what would you do differently?

Technical Trade-offsAdaptability & Ambiguity
Author's notes

Genuinely hard to answer in an interview because you don't want to sound like you made a disaster of the whole thing.

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AI HintsAI Generated

Suggested Approach

Choose a real product or GTM decision that didn't go as planned, and focus on what you learned and how you've changed your approach since. Be honest about your role in the outcome, but keep the tone forward-looking and growth-oriented.

Pro tip: Avoid picking a failure that was entirely outside your control; instead, choose one where you had agency and can clearly articulate the counterfactual. Show that you've turned the lesson into a repeatable process or principle you now apply.

1. Set the context

Briefly describe the product, goal, and your specific responsibility so the interviewer understands the stakes and your role.

2. State the decision and outcome

Explain what you did and what happened, including the negative result, without being defensive or blaming others.

3. Identify what you'd do differently

Clearly articulate the alternative approach you would take now, and why it would likely lead to a better outcome.

4. Extract the lesson

Summarize the broader principle or insight you gained, showing self-awareness and a growth mindset.

5. Show the change in action

Give a brief example of how you've applied this lesson in a later situation, proving you've actually changed your behavior.

Key Points to Mention

  • A specific GTM or product decision where you had ownership and the outcome was suboptimal.
  • The data or signals you missed or misinterpreted at the time.
  • The alternative approach you would take now, such as more customer discovery, a phased rollout, or better cross-functional alignment.
  • The personal lesson learned, e.g., the importance of validating assumptions early or involving engineering sooner.
  • How you've operationalized that lesson into a repeatable process or habit.
  • A brief, positive outcome from applying the lesson later, demonstrating growth.

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