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

Senior
Apr 2026

Summary

Part two of the eBay software engineer loop was a mix of leadership and system design, with the interviewer pushing hard on past project details. Less about theory, more about whether you actually made the calls you're claiming you made.

Questions Asked (3)

Q1

Walk me through a past project you led or contributed to significantly, and explain the technical decisions behind the design.

System DesignTechnical Trade-offs
Author's notes

This is the kind of question that sounds easy until you're mid-answer and realize you can't remember why you made half the choices you made two years ago.

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AI HintsAI Generated

Suggested Approach

Select a project where you made significant technical decisions, ideally one with scale or complexity relevant to eBay's e-commerce platform. Structure your answer using a clear narrative: context, problem, options considered, decision rationale, implementation, and results. Focus on trade-offs and how you balanced competing concerns like performance, scalability, and maintainability.

Pro tip: Quantify the impact of your decisions (e.g., latency reduction, cost savings, scalability improvements) and explicitly discuss what you would do differently in hindsight to show growth and self-awareness.

1. Set the Context

Briefly describe the project, your role, and the business or technical goals. Keep it concise to leave time for technical depth.

2. Define the Problem and Constraints

Explain the specific challenge you faced, including constraints like scalability, latency, budget, or legacy systems. This sets up the need for trade-offs.

3. Discuss Technical Options and Trade-offs

Present the alternatives you considered, compare them on dimensions like performance, complexity, cost, and maintainability, and justify why you chose your approach.

4. Explain Implementation and Challenges

Describe how you executed the design, any obstacles you overcame, and how you validated the solution (e.g., testing, monitoring).

5. Highlight Results and Learnings

Quantify the outcomes (e.g., improved latency, reduced costs) and reflect on what you learned or would change next time.

Key Points to Mention

  • Scalability and performance considerations (e.g., handling high traffic, data partitioning)
  • Trade-offs between consistency, availability, and partition tolerance (CAP theorem) if relevant
  • Choice of technologies (e.g., databases, caching, message queues) and why they fit the use case
  • Impact on business metrics (e.g., conversion rate, revenue, operational cost)
  • Collaboration with cross-functional teams (e.g., product, SRE, data science)
  • Lessons learned and how you applied them to future projects

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

Q2

What trade-offs did you consider in your design, and what did you end up deprioritizing and why?

Technical Trade-offsSystem Design
Author's notes

Tripped up here a bit.

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AI HintsAI Generated

Suggested Approach

Choose a specific project where you made deliberate trade-offs, and structure your answer around the decision-making process: what options you considered, the criteria you used (e.g., scalability, latency, cost, time-to-market), and why you deprioritized certain aspects. Be transparent about the consequences of your choices and how you mitigated risks, showing that you understand engineering is about balancing constraints.

Pro tip: Quantify the impact of your trade-offs (e.g., 'we accepted 100ms extra latency to reduce infrastructure cost by 30%') and mention how you validated the decision with data or user feedback. This demonstrates that your choices were intentional and outcome-driven, not arbitrary.

1. Set the context

Briefly describe the project, your role, and the key constraints (e.g., tight deadline, limited resources, high traffic). This helps the interviewer understand the environment in which you made trade-offs.

2. List the options and criteria

Explain the alternative designs or approaches you considered and the criteria you used to evaluate them (e.g., performance, scalability, maintainability, cost, development effort).

3. Explain the trade-offs

Detail the pros and cons of each option, focusing on what you would gain and lose with each. Highlight the most critical trade-off that drove your decision.

4. State what you deprioritized and why

Clearly say which aspect(s) you chose to deprioritize (e.g., feature completeness, optimal performance, perfect consistency) and justify why it was acceptable given the context and goals.

5. Discuss outcomes and lessons

Share the results of your decision, any metrics that validated it, and what you learned. Mention how you might revisit the trade-off in the future if constraints change.

Key Points to Mention

  • Specific trade-off dimensions: e.g., consistency vs. availability, latency vs. throughput, build vs. buy, monolith vs. microservices.
  • Business or user impact of the deprioritized aspect: e.g., 'we accepted eventual consistency because real-time updates weren't critical for the MVP.'
  • Quantitative data or metrics that informed the decision and measured the outcome.
  • Stakeholder alignment: how you communicated the trade-offs to product managers, designers, or leadership.
  • Risk mitigation: what you did to reduce the impact of the deprioritized aspect (e.g., feature flags, monitoring, fallback mechanisms).
  • Future considerations: under what conditions you would revisit the decision (e.g., scaling to 10x users, new requirements).

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

Q3

What problems did you run into during the project, and how did you resolve them?

Root Cause AnalysisAdaptability & Ambiguity
Author's notes

Went fine.

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AI HintsAI Generated

Suggested Approach

Choose a specific project and describe 1-2 concrete technical or process problems you encountered, focusing on your root cause analysis and the actions you took to resolve them. Emphasize the measurable outcome and what you learned, showing adaptability and a structured problem-solving mindset.

Pro tip: Pick a problem where you initially made a wrong assumption or hit a dead end, then explain how you pivoted—this demonstrates intellectual honesty and adaptability, which interviewers value more than a flawless story.

1. Set the context

Briefly describe the project, your role, and the goal so the interviewer understands the stakes and your responsibilities.

2. Define the problem

Clearly state the specific problem you encountered, including its impact on the project (e.g., delays, bugs, performance issues).

3. Explain your root cause analysis

Walk through how you investigated the problem—what data you gathered, tools you used, and how you identified the underlying cause.

4. Describe your resolution

Detail the steps you took to fix the problem, including any trade-offs, collaboration, or iterations involved.

5. Share the outcome and learning

Quantify the result (e.g., reduced latency by X%, saved Y hours) and reflect on what you learned or how you prevented similar issues in the future.

Key Points to Mention

  • Root cause analysis techniques (e.g., 5 Whys, fishbone diagram, debugging tools)
  • Collaboration with cross-functional teams (e.g., product, QA, DevOps) to resolve the issue
  • Adaptability when initial solutions failed or requirements changed
  • Quantifiable impact of the resolution (e.g., performance improvement, cost savings)
  • Lessons learned and preventive measures for future projects
  • Clear communication of technical details to both technical and non-technical stakeholders

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