Introduction

The News Feed system design interview is a common question at Meta (Facebook) and other large tech companies. This interview tests your ability to design a scalable, real-time, and personalized feed system.

1. Understanding the Problem Statement

What is a News Feed?

• A personalized stream of posts from friends, pages, and groups.
• Includes text, images, videos, and ads.
• Ordered by relevance using ranking algorithms.

Functional Requirements

• Users should see personalized content.
• Posts should be ranked based on relevance.
• The system should support high read and write traffic.
• Real-time updates should be pushed to users.

Non-Functional Requirements

• Low latency (fast loading of feed).
• High availability and scalability.
• Support billions of users.

2. High-Level Architecture

The News Feed system consists of:

• Write Path: Handling posts from users.
• Read Path: Fetching and ranking personalized content.
• Storage: Handling large-scale data efficiently.

Architecture Diagram

[User] → [API Gateway] → [Load Balancer] → [Write Service] → [Storage]
                                  ↓
                            [Feed Generation Service]
                                  ↓
                              [Ranking System]
                                  ↓
                             [Feed Cache]
                                  ↓
                               [User]

3. Database & Storage

Post Storage

• Use NoSQL (Cassandra, DynamoDB) for high write throughput.
• Store posts with metadata (user ID, timestamp, likes, comments).

User Graph Storage

• Use Graph Database (Neo4j, Amazon Neptune) to store connections between users.

Feed Storage & Caching

• Use Redis to cache generated feeds for fast retrieval.
• Store ranked lists for quick access.

4. Feed Generation Strategies

Pull Model (On-Demand Generation)

• Generate feed when a user requests it.
• Pros: Fresh data.
• Cons: High latency.

Push Model (Precomputed Feeds)

• Compute feeds in advance and store them in cache.
• Pros: Low latency.
• Cons: High storage cost.

Hybrid Model (Combination of Push & Pull)

• Precompute for active users, fetch on-demand for inactive users.

5. Ranking & Personalization

Ranking determines which posts appear at the top. Factors include:

• Engagement Score (likes, shares, comments)
• Recency (newer posts get higher ranking)
• User Affinity (closer friends get priority)
• Content Type (images, videos may be prioritized)
• Ad Relevance (personalized ad targeting)

Machine Learning for Ranking

• Train models using past interactions to predict engagement.
• Use collaborative filtering for recommendations.

6. Handling Scale & Real-Time Updates

Scalability Strategies

• Sharding & Partitioning: Distribute data across multiple servers.
• Load Balancers: Route requests to prevent overloading.

Real-Time Updates

• WebSockets: Push updates instantly.
• Kafka/Event Streaming: Handle millions of feed updates.

7. Handling Failures & Monitoring

• Replicate Data across multiple regions.
• Circuit Breakers prevent system overload.
• Monitoring with Prometheus & Grafana.

8. Interview Approach

Step 1: Clarify Requirements

• Ask about real-time updates, ranking complexity, scale.

Step 2: Define High-Level Architecture

• Sketch the major components (API Gateway, Storage, Ranking).

Step 3: Discuss Data Storage

• Choose databases for posts, user graph, and caching.

Step 4: Explain Feed Generation

• Compare Pull, Push, and Hybrid models.

Step 5: Discuss Ranking & Scaling

• Show how ML and real-time systems improve ranking.

Step 6: Handle Edge Cases

• What happens if a server goes down?
• How do you deal with spam or fake news?

Conclusion

Designing Facebook’s News Feed requires balancing scalability, ranking, and real-time performance. By following a structured approach, you can confidently tackle this system design interview. 🚀

For more resources:

• https://engineering.fb.com/
• https://github.com/donnemartin/system-design-primer