← Databricks Interview Insights

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

SeniorPrefer not to say
May 2026

Summary

Databricks system design round focused entirely on a VM allocation service. One question, fairly scoped, but there's more depth hiding in it than you'd expect from the initial prompt.

Questions Asked (1)

Q1

Design a service that allocates VMs by attaching them to free IPv4 addresses from a shared pool. Cover the API surface, database schema for the IP pool and allocation records, and the request workflow for attaching and detaching a VM to an IP.

System DesignAPI & IntegrationsData Modeling
Author's notes

My first instinct was to jump straight into the schema and I had to pull myself back.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying requirements (scale, consistency, failure handling) and then present a high-level design covering API, data model, and workflow. Emphasize concurrency control and idempotency to ensure correct IP allocation and release.

Pro tip: Use database transactions with SELECT FOR UPDATE SKIP LOCKED to atomically claim a free IP, and make the attach/detach endpoints idempotent to handle retries safely.

1. Clarify Requirements and Scope

Ask about scale (number of IPs, VMs, requests per second), consistency needs, and failure scenarios. Define the core operations: attach, detach, and possibly list/query.

2. Design the API Surface

Define RESTful endpoints: POST /vms/{vm_id}/ip to attach, DELETE /vms/{vm_id}/ip to detach, and GET /ips to list available IPs. Include request/response schemas and status codes.

3. Design the Database Schema

Create tables: ip_pool (ip_address, status, vm_id, updated_at) and allocation_records (id, vm_id, ip_address, attached_at, detached_at). Use indexes on status and vm_id for efficient queries.

4. Define the Request Workflow

For attach: validate VM, begin transaction, select a free IP with locking, update IP status and vm_id, insert allocation record, commit. For detach: validate, begin transaction, update IP status to free, update allocation record, commit.

5. Address Concurrency, Failures, and Idempotency

Use transactions and row-level locks to prevent double allocation. Implement idempotency keys for attach/detach to handle retries. Discuss failure recovery and monitoring.

Key Points to Mention

  • Concurrency control: use SELECT FOR UPDATE SKIP LOCKED or optimistic locking to avoid race conditions.
  • Idempotency: ensure attach/detach operations are idempotent using request IDs or unique constraints.
  • Database schema: separate tables for IP pool and allocation history for audit and debugging.
  • API design: RESTful endpoints with clear status codes (200, 201, 409, 404) and error responses.
  • Failure handling: retries, timeouts, and compensating transactions for partial failures.
  • Scalability: consider sharding or partitioning the IP pool if the number of IPs is very large.

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