Design an Audit Log System

Requirements

• •Ingest audit events from services (who, did what, to which resource, when, from where)
• •Guarantee no audit events are lost in transit even if the storage backend is temporarily unavailable
• •Provide tamper-evident storage: any modification to historical records must be detectable
• •Support querying logs by actor, resource type, action, and time range with < 1 second latency
• •Support compliance export: bulk export of all events for a given tenant or time range

Non-Functional Requirements

• •Audit event ingestion latency < 100ms
• •Zero event loss guarantee (durable queue before write)
• •Query latency < 1 second for 30-day time ranges
• •7-year retention with tiered storage (hot 90 days, warm 1 year, cold archive)

Constraints

• •Logs must be immutable after writing — no update or delete operations
• •Compliance requirement: SOC 2 and GDPR; logs must be retained for 7 years
• •Audit events come from dozens of internal microservices

Evaluation Criteria