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

SeniorPrefer not to say

Jul 2026

Summary

System design round at Microsoft for a SWE role. One question, pretty meaty, focused on secrets management infrastructure. Left feeling like I had more to say but ran out of time.

Questions Asked (1)

Design a secure secrets management service that stores and retrieves secrets, certificates, and keys for applications and users, similar to Azure Key Vault.

System DesignTechnical Trade-offsAPI & Integrations

Author's notes

I jumped straight into the API layer which was probably the wrong move.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements (scale, compliance, multi-tenancy, latency) and then present a high-level architecture covering storage, encryption, access control, and auditing. Dive into key components like HSM-backed key management, envelope encryption, and API design, while discussing trade-offs around consistency, availability, and security.

Pro tip: Emphasize the importance of separating the control plane (management) from the data plane (secret retrieval) to achieve scalability and security isolation, and mention how you would handle key rotation without downtime.

1. Clarify Requirements and Scope

Ask questions to understand scale (requests per second, number of secrets), compliance needs (FIPS, GDPR), multi-tenancy, and latency requirements. Define the types of secrets (passwords, certificates, keys) and user roles.

2. High-Level Architecture

Outline the main components: API gateway, authentication/authorization service, secret storage (encrypted), key management service (HSM-backed), audit logging, and replication for availability. Explain how they interact.

3. Security and Encryption Design

Describe the encryption strategy: envelope encryption with a master key in HSM, per-secret data encryption keys, and automatic key rotation. Cover access control (RBAC, policies) and auditing of all access.

4. API and Integration

Design RESTful APIs for CRUD operations on secrets, with versioning and soft-delete. Discuss SDKs, integration with Azure AD for auth, and how applications retrieve secrets securely (e.g., managed identities).

5. Trade-offs and Scalability

Discuss trade-offs: consistency vs. availability (e.g., using quorum reads/writes), caching vs. security, and cost of HSM. Explain how to scale horizontally and handle failures (replication, backups).

Key Points to Mention

Envelope encryption with HSM-backed master keys and automatic rotation
Separation of control plane and data plane for scalability and security
Fine-grained access control using RBAC and Azure AD integration
Comprehensive audit logging and monitoring for compliance
API design with versioning, soft-delete, and idempotency
Multi-tenancy and isolation strategies (e.g., per-tenant encryption keys)

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