Design a scalable Instagram-like platform

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Quick Overview

Design a scalable Instagram-like platform evaluates requirements, scale assumptions, API/data design, architecture, trade-offs, failure modes, and rollout in a realistic interview setting. A strong answer states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

Design a scalable Instagram-like platform

Company: DoorDash

Role: Software Engineer

Category: System Design

Difficulty: hard

Interview Round: Technical Screen

Design an Instagram-like photo/video sharing platform. Requirements: users sign up, follow others, upload media, view a personalized home feed, like/comment, receive notifications, and search; stories and direct messages are optional. Provide APIs, data models, and high-level architecture. Explain media ingestion, storage, thumbnailing/transcoding, and CDN delivery. Describe feed generation and ranking (pull vs push, fan-out strategies), caching layers, timelines, and handling hot accounts. Discuss consistency vs availability trade-offs, sharding and partitioning, indexes, and read/write scaling. Address privacy, abuse/spam mitigation, observability, cost controls, and multi-region disaster recovery. Include back-of-the-envelope capacity estimates and an evolution plan from MVP to planet scale.

Overview: Design a scalable Instagram-like platform evaluates requirements, scale assumptions, API/data design, architecture, trade-offs, failure modes, and rollout in a realistic interview setting. A strong answer states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

Read the full DoorDash Software Engineer interview experience this question came from

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DoorDash
Jul 17, 2025
hardSoftware EngineerTechnical ScreenSystem Design
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Design a scalable Instagram-like platform

Design: Instagram-like Photo/Video Sharing Platform (Technical Screen)

Context

Design a photo/video sharing platform with core social features and a personalized feed. Optimize for large-scale read-heavy workloads and mobile clients. Optional features (stories, DMs) may be stubbed but need not be fully designed.

Requirements

  1. Core features
    • User sign-up/login, follow/unfollow
    • Upload photos/videos
    • Personalized home feed
    • Likes, comments
    • Notifications
    • Search (users, hashtags, captions)
    • Optional: stories, direct messages (outline only)
  2. Deliverables
    • Public APIs (CRUD and feed endpoints)
    • Data models and key indexes
    • High-level architecture and components
    • Media ingestion pipeline: upload, storage, thumbnailing/transcoding, CDN delivery
    • Feed generation and ranking: pull vs push, fan-out strategies, timelines, caching, handling hot accounts
    • Consistency vs availability trade-offs
    • Sharding/partitioning strategy and read/write scaling
    • Privacy and access control
    • Abuse/spam mitigation
    • Observability (metrics, logging, tracing)
    • Cost controls
    • Multi-region disaster recovery
    • Back-of-the-envelope capacity estimates
    • Evolution plan from MVP to planet scale

Clarifying Questions to Ask Guidance

  • Clarify users, core use cases, read/write patterns, scale, latency, availability, and data retention.
  • State explicit assumptions before making sizing or architecture decisions.
  • Prioritize the functional path first, then address reliability, security, observability, and rollout.

What a Strong Answer Covers Guidance

  • A scoped requirements summary with concrete non-goals and success metrics.
  • API, data model, architecture, consistency, capacity, and operations.
  • Reasoned trade-offs among simple and scalable designs, including bottlenecks and failure modes.
  • A validation, monitoring, migration, and launch plan appropriate for the risk level.

Follow-up Questions Guidance

  • What breaks first at 10x traffic or data volume?
  • How would you degrade gracefully during dependency failures?
  • What metrics and alerts would prove the design is healthy after launch?

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