← Apple Interview Insights

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

SeniorPrefer not to say
May 2026

Summary

Apple system design round, one massive question that basically asked you to redesign a fintech product from scratch. The scope was brutal and I'm not sure I covered even half of it well.

Questions Asked (1)

Q1

You're running a monolithic digital wallet and P2P payments app. Walk through how you'd migrate it to microservices, covering service boundaries, data ownership, API design, cross-service transaction patterns, consistency, compliance, observability, and rollout strategy. Include a phased plan, key risks, and how you'd measure success.

System DesignTechnical Trade-offsAPI & Integrations
Author's notes

This question is basically five questions duct-taped together.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying the scope and constraints, then propose a phased migration using the Strangler Fig pattern to incrementally extract services while maintaining a working monolith. Structure your answer around the key areas: service boundaries, data ownership, API design, cross-service transactions, consistency, compliance, observability, and rollout, and tie each to concrete trade-offs and success metrics.

Pro tip: Emphasize that in payments, correctness and compliance trump speed—show you'd prioritize idempotency, auditability, and regulatory requirements over microservices dogma, and that you'd measure success by business KPIs (e.g., transaction success rate, latency) not just technical metrics.

1. Clarify Requirements and Constraints

Ask about scale, latency, compliance (PCI-DSS, PSD2, GDPR), existing pain points, and team structure to tailor your approach. This shows you avoid over-engineering and focus on real needs.

2. Define Service Boundaries and Data Ownership

Identify bounded contexts (e.g., user, wallet, payments, notifications) using domain-driven design, and assign each service exclusive ownership of its data to avoid shared databases. Discuss how to handle cross-service queries via APIs or materialized views.

3. Design APIs and Cross-Service Transactions

Propose REST/gRPC APIs with versioning, idempotency, and authentication. For transactions, use sagas with compensating actions or orchestration, and discuss consistency models (eventual vs. strong) and how to handle failures.

4. Address Compliance, Observability, and Rollout

Explain how to maintain PCI-DSS compliance (e.g., tokenization, audit logs), implement distributed tracing, logging, and metrics, and plan a phased rollout (strangler fig, canary releases) with rollback strategies.

5. Measure Success and Mitigate Risks

Define success metrics (e.g., transaction success rate, latency, error rates, deployment frequency) and identify key risks (data consistency, latency, operational complexity) with mitigation plans.

Key Points to Mention

  • Strangler Fig pattern for incremental migration, starting with low-risk services like notifications.
  • Domain-driven design to define bounded contexts and avoid distributed monolith.
  • Saga pattern (orchestration vs. choreography) for cross-service transactions with compensating actions.
  • Idempotency and exactly-once processing to handle retries and ensure correctness in payments.
  • Compliance considerations: PCI-DSS, data residency, audit trails, and encryption.
  • Observability: distributed tracing (e.g., OpenTelemetry), centralized logging, and metrics with SLOs.

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