System Design Mock Interview: Design Instagram

Summary

This video script offers a comprehensive guide on building a scaled-down version of Instagram, focusing on system design for a system that supports 10 million users. It covers understanding requirements, brainstorming features, and considering scalability. The speaker discusses database choices, data modeling, API design, and the architecture of application services, including caching strategies and load balancing. The script also touches on generating user feeds and the importance of efficient data storage and retrieval.

Takeaways

• 📚 The video discusses a system design interview question similar to those asked by tech giants like Facebook, Google, and Amazon, focusing on building a scaled-down version of Instagram.
• 🤔 The presenter emphasizes the importance of understanding the problem and requirements before diving into the design, including brainstorming features and considering the application's scale.
• 📱 The basic requirements outlined include the ability to upload images from mobile clients, allowing users to follow others, generating a news feed, and designing for scalability to support 10 million users.
• 🔢 A hypothetical scenario is presented where 10 million monthly active users upload two 5-megabyte photos each, leading to significant data and storage considerations.
• 🗄️ The video suggests a relational database for storing user, photo, and follower data due to the inherent relational nature of the information, with a preference for SQL databases like MySQL or PostgreSQL.
• 🏢 The data model includes tables for users, photos, and followers, with considerations for primary and foreign keys to establish relationships between the data.
• 🖼️ For handling the large photo files, a distributed file system like Amazon S3 is recommended for storage and replication, with references stored in the database.
• 🔄 The system design includes application service layers for handling CRUD operations, differentiated into read and write services to optimize performance and scalability.
• 🔄 The use of caching, such as Redis, is suggested to improve efficiency, particularly for read-heavy operations, with a write-through cache policy to maintain data consistency.
• 🌐 A load balancer is crucial for distributing client requests across multiple servers to ensure no single server becomes a bottleneck, supporting the system's scalability.
• 🚀 The concept of a feed generation service is introduced to preprocess and cache user feeds, reducing the computational load during user requests and ensuring fresh content delivery.

Q & A

What is the primary goal of the video?

The primary goal of the video is to demonstrate how to approach and answer a system design interview question, specifically by designing a simplified version of Instagram.

What is the first step recommended when beginning a system design interview?

The first step recommended is to take a moment to understand the question and the problem, then go through the requirements and features needed for the system.

What are the four main requirements outlined for the Instagram-like system?

The four main requirements are: the ability to upload images from a mobile client, allowing users to follow other users, generating and displaying a news feed of images, and designing the system to scale up to support 10 million users.

How is the monthly data storage requirement calculated for the system?

The monthly data storage requirement is calculated by assuming 10 million users, each uploading two photos per month, with each photo being around 5 megabytes. This results in 100 million megabytes (or 100 terabytes) per month, and 1.2 petabytes per year.

What types of data need to be stored in the system?

The types of data that need to be stored include users, photos, and the relationships between users (following model).

Why is a relational database suggested for this system?

A relational database is suggested because the data has clear relationships, such as users to photos and users following other users, which benefits from relational queries.

What are the key fields included in the user table of the database?

The key fields in the user table include an ID (primary key), name, email address, location, and potentially other attributes like timezone.

How is the photo data stored and referenced in the database?

Photo data includes an ID (primary key), a foreign key referencing the user, a caption or description, location metadata, and a path or URL referencing the file stored in a distributed object storage system like S3.

How are user relationships modeled in the database?

User relationships are modeled in a separate followers table, which includes two columns: user1 (the follower) and user2 (the followee), both of which are foreign keys referencing the user table.

What are the roles of the read and write services in the application?

The read service is responsible for fetching and returning data to users, utilizing caching for efficiency, while the write service handles data uploads and updates, ensuring that new content is stored in both the database and cache.

What is the purpose of the load balancer in the system?

The load balancer's purpose is to distribute incoming requests evenly across multiple application servers to prevent any single server from becoming overloaded, ensuring the system can handle high volumes of traffic efficiently.

How is the news feed of images generated and served to users?

The news feed is generated by a separate feed generation service that precomputes the feed content based on new images and user relationships, stores it in the cache, and serves it quickly to users when requested.