Practice: Design TikTok

Short-video platform inspired by TikTok: async transcoding into adaptive-bitrate renditions, CDN playback with prefetch, a two-stage For You recommender (retrieval, then ranking) and near-real-time learning from engagement, as described in ByteDance's Monolith paper (2022). A teaching design, not ByteDance's internal architecture.

Build this system yourself on the canvas below. Add components, connect them, and run traffic simulations to see where your design holds up and where it breaks.

Functional requirements

  • Creators can upload short videos with captions, hashtags, music, and thumbnails.
  • Users can watch videos with low-latency playback and scroll through a personalized For You feed.
  • Users can like, comment, share, follow creators, and save/favorite videos.
  • The platform should support creator profile pages and creator video lists.
  • The system should support near-real-time feed personalization and cold-start recommendations.
  • The platform should support content moderation, policy enforcement, and copyright/takedown workflows.
  • The system should support creator analytics and trending/viral content detection.
  • The platform should support ad insertion and live-commerce or promotional content hooks.

Non-functional requirements

  • Video playback should start quickly on mobile networks with ABR and global edge delivery.
  • Upload requests should return quickly while heavy processing runs asynchronously.
  • The recommendation path should stay low-latency even when offline feature pipelines lag.
  • The platform should survive viral spikes and hot objects without overwhelming origin systems.
  • Moderation, copyright, and policy systems should be isolated so they don’t block the core watch path unnecessarily.
  • The system should remain available during regional failures with clear RPO/RTO and safe rollout controls.
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Round 1 of 4 · Architecture Design · 60:00 remaining
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    Components

    User
    CDN
    Load Balancer
    Server
    Cache
    Database
    Blob Storage
    Search Index
    Queue
    Worker
    Rate Limiter
    Service
    API Gateway
    Reverse Proxy
    WebSocket Server
    Third-party API

    Inspector

    Notes
    Use clear names so your design intent is easy to understand.
    Good
    Name by business meaning
    "Order API", "Restaurant Service"
    Avoid
    Generic names = zero signal
    "Server 1", "API", "Queue"
    A short description for each component makes feedback much better.
    100%
    Start by identifying:
    • Users & entry points
    • APIs & services
    • Databases & storage
    • Traffic flow & scale

    Round 1 of 4 Architecture Design

    Run a simulation to see results.

    Time Remaining
    60:00
    System Design Interview

    What are the core functional requirements?
    What are the key non-functional constraints?

    Questions

    Start Evaluation to unlock questions.

    EVALUATE MODE

    Test yourself like it's the real thing.

    A structured 4-module evaluation that mirrors how top companies assess system design candidates.

    Architecture Design
    Draw your system on the canvas. Define components, connections, and data flow.
    FR & NFR Requirements
    Answer functional and non-functional requirement questions about your design.
    MCQ Round
    Multiple choice questions testing your depth on the chosen system.
    Tradeoff Analysis
    Justify your design decisions and defend your architectural tradeoffs.
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    • 30 min
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    • 60 min
    Round 2 of 4
    MCQ Round
    Answer multiple-choice questions based on your design.

    Exit Interview?

    You're in the middle of an interview session. Leaving now will end your current attempt.

    Your progress will be saved.

    Open a saved design

    Select a design to load into the canvas.

    My Evaluations

    Your past evaluation sessions

    Here’s a simple request flow that follows the expected layer order.

    External User
    →
    Edge CDN → API Gateway → Load Balancer
    →
    Compute App Servers / Services
    →
    DataAccess Cache
    →
    Storage Database / Search Index
    →
    Async Queue → Worker

    Tip: keep arrows moving forward through layers (Edge → Compute → Storage). Avoid sending storage back to compute.

    Evaluation Instructions

    Read the rules carefully before starting. The test auto-submits on refresh.

    Before you start

    • Build your architecture on the canvas. The timer starts when you click Start Evaluation.
    • Don't forget to answer Functional Requirement and Non Functional Requirements.
    • When satisfied with your design, click Next to lock it and view the questions.
    • Please answer final step questions to complete the evaluation.

    Dos

    • Do read each question carefully before answering.
    • Do include required components to maximize component coverage.
    • Do save a copy of your design if you want to keep it before submission.

    Don'ts

    • Don't refresh or close the tab during an active evaluation — this will auto-submit your answers.
    • Don't switch app modes or open another tab while the evaluation is running.
    • Don't attempt to edit the design after clicking Next; the workspace will be locked.

    All the best!!

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    SYSTEM BRIEF

    System Constraints

    What the system must do — every item is a user-facing behaviour your architecture must support.

      ↑ Engineering Constraints

      These are the failure modes you must design against — latency SLAs, durability targets, traffic ceilings.

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