Problem and Scope
Design a system like Netflix that allows users to browse, stream, and interact with video content. Focus on the core platform including video delivery and user interactions.
Start by confirming the core user journey, exclusions, success criteria, and the constraints that materially affect the architecture.
Requirements to Clarify
A strong answer should establish scope before choosing components.
Functional requirements:
- Users should be able to browse and select video content
- Users should be able to stream videos with minimal buffering
- System should track user viewing history and preferences
- System should collect user activity data for recommendations
- Users should be able to resume watching from where they left off
Non-functional requirements:
- The system should have low latency for video streaming globally
- The system should be highly available
- The system should handle a large catalog of videos
- The system should support millions of concurrent users
- The system should efficiently store and deliver large video files
Scale and Capacity
Use the workload to justify storage, partitioning, caching, and reliability decisions. Clarify or challenge these assumptions rather than treating them as unquestionable facts:
- Approximately 200 million users worldwide
- About 10,000 titles in the content library
- Average video length of 1 hour
- Videos available in multiple resolutions (SD, HD, 4K)
- High read-to-write ratio (many more views than content additions)
Architecture Discussion
Walk through the important read and write paths, identify ownership boundaries, and explain how the design behaves when dependencies fail. Cover these areas explicitly:
- Content storage and delivery system
- User metadata storage
- Video metadata storage
- Global content delivery network
- API services for user interactions
- Data processing systems for analytics and recommendations
- Caching mechanisms at multiple levels
- Efficiently storing and delivering large video files globally
- Handling diverse connection speeds and device capabilities
- Managing metadata for both videos and user activities
- Collecting and processing user activity data for recommendations
- Ensuring high availability and low latency worldwide
Follow-up Questions
Expect the interviewer to test the consequences of your choices. Practise answering these questions with a concrete decision, its benefit, and its cost:
- How would your design handle global distribution of content?
- Focus: Assess the candidate's answer to "How would your design handle global distribution of content" for explicit assumptions, a workable mechanism, failure behavior, and consequential trade-offs.
- What approach would you take to store and manage the video files?
- Focus: Assess the candidate's answer to "What approach would you take to store and manage the video files" for explicit assumptions, a workable mechanism, failure behavior, and consequential trade-offs.
- How would you design the system to collect and process user activity data?
- Focus: Assess the candidate's answer to "How would you design the system to collect and process user activity data" for explicit assumptions, a workable mechanism, failure behavior, and consequential trade-offs.
- What trade-offs did you consider when choosing your storage solutions?
- Focus: Assess the candidate's answer to "What trade-offs did you consider when choosing your storage solutions" for explicit assumptions, a workable mechanism, failure behavior, and consequential trade-offs.
- How would your system scale to handle more users or content?
- Focus: Assess the candidate's answer to "How would your system scale to handle more users or content" for explicit assumptions, a workable mechanism, failure behavior, and consequential trade-offs.
Evaluation Rubric
MockMe evaluates the answer across the following dimensions. A complete answer should connect claims to requirements and explain consequential trade-offs.
- Requirements and scope (15%): Clarifies and prioritizes the required behavior for Users should be able to browse and select video content; Users should be able to stream videos with minimal buffering; System should track user viewing history and preferences. Establishes the constraints that materially affect Design Netflix, including The system should have low latency for video streaming globally; The system should be highly available. Strong evidence includes Separates the critical path from secondary features and resolves ambiguous requirements before choosing components.
- Architecture and interfaces (20%): Presents coherent ownership boundaries and end-to-end flows covering Content storage and delivery system; User metadata storage; Video metadata storage; Global content delivery network. Strong evidence includes Defines interfaces and traces important success, retry, and failure paths across the proposed components.
- Data and scaling (25%): Uses workload assumptions such as Approximately 200 million users worldwide; About 10,000 titles in the content library to justify capacity and partitioning decisions. Explains the data, state, or model strategy for Content storage and delivery system; User metadata storage; Video metadata storage. Strong evidence includes Quantifies a dominant workload, identifies the first bottleneck, and explains how the design evolves as that workload grows.
- Reliability, correctness, and safety (20%): Explains concrete failure behavior, recovery, and operational safeguards for Ensuring high availability and low latency worldwide; The system should be highly available. Strong evidence includes States the required correctness or consistency boundary and covers retries, partial failure, observability, and safe degradation.
- Communication and trade-offs (20%): Drives a structured discussion and compares consequential alternatives for Managing metadata for both videos and user activities; Collecting and processing user activity data for recommendations; Ensuring high availability and low latency worldwide. Strong evidence includes Makes assumptions explicit, answers the question asked, and explains both the benefit and cost of major decisions.