Design a resource change tracking database

Q: Design a resource change tracking database

This is a System Design interview question from Microsoft for Software Engineer roles. View the full question and solution on PracHub.

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Question

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Scenario

You are building part of an Azure-like cloud control plane. Resources (VMs, networks, storage accounts, etc.) are stored as JSON documents and are updated frequently.

Task

Design a Resource Change Database / system that:

Captures every change to a resource (create/update/delete).
Emits a notification/event after a change occurs.
Downstream consumers can use the notification to query the “diff” (what changed between the old and new versions) and store that diff for later auditing/search.

Requirements

Correctness: Diffs must correspond to the actual committed change.
Ordering: For a given resource, changes should be processed in order.
Idempotency: Duplicate notifications should not create duplicate diff records.
Query: Support querying change history by resource ID and time range; optionally filter by fields changed.
Scale: Assume high write volume (control-plane scale) and many resource types.

Clarifications you may decide

How diffs are represented (JSON Patch, field-level records, full before/after snapshots).
Retention policy (e.g., keep 90 days of diffs).
Multi-region requirements and latency SLOs.

Design a resource change tracking database

Scenario

Task

Requirements

Clarifications you may decide

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