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System Design: Instagram-like Application

Problem Statement

Design a large-scale photo and video sharing platform similar to Instagram, where users can upload photos and videos, follow other users, like and comment on posts, view stories, and interact with content in real time. The system should support a massive user base and provide high availability, low latency, and scalability.

Requirements

Functional Requirements:

  1. User Registration and Authentication: Users should be able to sign up, log in, and manage their profiles.
  2. Photo and Video Upload: Users can upload and share photos or videos with their followers.
  3. Feed: Display a feed of posts from users that the current user follows, ordered by relevance or time.
  4. Likes and Comments: Users can like and comment on posts.
  5. Stories: Users can post short-lived content (photos or videos) that disappears after 24 hours.
  6. Notifications: Notify users about likes, comments, follows, and other interactions.
  7. Search and Explore: Users can search for content, hashtags, and profiles. An explore section shows trending content.
  8. Direct Messaging (DM): Users can send private messages to each other.
  9. Follow/Unfollow: Users can follow or unfollow other users.
  10. Reels (Optional): Support for short videos similar to TikTok.

Non-Functional Requirements:

  1. Scalability: The system should support millions of users and handle billions of posts.
  2. High Availability: The platform should have minimal downtime and be available 24/7.
  3. Low Latency: Posts, likes, and comments should appear with minimal delay.
  4. Data Privacy and Security: Ensure secure handling of user data and privacy controls.
  5. Consistency: The system should ensure eventual consistency in displaying posts, likes, and comments.

Components of the System

The Instagram-like system can be broken down into the following key components:

  1. User Service: Manages user registration, authentication, and profile management.
  2. Post Service: Handles photo and video uploads, storage, and retrieval.
  3. Feed Service: Generates personalized feeds based on the users a person follows.
  4. Story Service: Manages user stories that are visible for 24 hours.
  5. Comment and Like Service: Allows users to like and comment on posts.
  6. Search and Explore Service: Handles search queries for users, hashtags, and posts.
  7. Notification Service: Notifies users about interactions (likes, comments, follows).
  8. Direct Messaging Service: Manages private messages between users.
  9. Media Storage: Stores user-uploaded media such as photos, videos, and stories in blob storage.

High-Level Design

  1. User Interface (UI): Users can upload photos and videos, browse their feed, view stories, search for content, and interact with posts.
  2. API Layer: Provides APIs for user registration (POST /register), uploading posts (POST /upload), retrieving the feed (GET /feed), and more.
  3. Service Layer:
    • User Service: Handles user registration, login, and profile management.
    • Post Service: Manages photo/video uploads, processing, and retrieving posts.
    • Feed Service: Generates the user's feed by fetching posts from followed users.
    • Story Service: Manages ephemeral stories that disappear after 24 hours.
    • Like and Comment Service: Handles liking and commenting on posts.
    • Search Service: Manages search queries for users, hashtags, and posts.
    • Notification Service: Sends notifications for user interactions.
  4. Storage Layer:
    • Database: Stores user profiles, posts, comments, likes, and follow relationships.
    • Blob Storage: Stores large media files such as photos, videos, and stories.
    • Cache: Stores frequently accessed data like popular posts, recent posts, and user profiles.

Detailed Design

1. User Registration and Authentication

Users should be able to register using email or phone number and third-party OAuth (e.g., Google, Facebook). Users can log in, manage their profiles, and set privacy controls.

Database Schema for Users:

Field Type Description
user_id String (PK) Unique identifier for the user.
username String Unique username chosen by the user.
email String User’s email address.
phone_number String User’s phone number.
profile_pic Blob User’s profile picture.
bio String User’s bio or description.
followers Integer Number of followers the user has.
following Integer Number of users the user is following.
privacy Boolean Whether the user profile is private.

Key Operations:

  • Registration/Login: Users can register and log in via email/phone or third-party services.
  • Profile Management: Users can update their bio, profile picture, and privacy settings.

2. Post Management (Photo/Video Upload)

Users can upload photos and videos to share with their followers. Media is uploaded to blob storage and metadata (caption, hashtags) is stored in the database.

Post Upload Flow:

  1. User uploads a photo or video along with a caption.
  2. The media is uploaded to blob storage (e.g., AWS S3), and a URL is returned.
  3. Metadata (caption, hashtags, user ID, timestamp) is stored in the database.
  4. Followers of the user will see the post in their feed.

Database Schema for Posts:

Field Type Description
post_id String (PK) Unique identifier for the post.
user_id String (FK) ID of the user who created the post.
media_url String URL of the photo/video in blob storage.
caption Text Text caption for the post.
hashtags Array[String] List of hashtags associated with the post.
timestamp Timestamp Time when the post was uploaded.
likes Integer Number of likes on the post.
comments Integer Number of comments on the post.

3. Feed Generation

The feed service fetches posts from users the current user follows and displays them in chronological or relevance order.

Feed Generation Process:

  1. When a user opens the app, the system retrieves a list of users they follow.
  2. The system fetches recent posts from these users and orders them by time or relevance.
  3. The feed is displayed to the user with posts, captions, and media.

Feed Table (Cache):

Field Type Description
user_id String (PK) ID of the user viewing the feed.
feed Array[String] List of post IDs for the user’s feed.
last_updated Timestamp Time when the feed was last updated.

4. Likes and Comments

Users can like or comment on posts. The system updates the number of likes and stores comments for each post.

Like and Comment Flow:

  1. When a user likes a post, the likes count is incremented, and the post owner is notified.
  2. Users can add comments to posts, which are stored with the post ID and displayed below the post.

Like/Comment Schema:

Field Type Description
like_id String (PK) Unique identifier for the like.
post_id String (FK) ID of the post being liked.
user_id String (FK) ID of the user who liked the post.
timestamp Timestamp Time when the post was liked.
comment_id String (PK) Unique identifier for the comment.
comment_text Text Text of the comment.

5. Stories

Stories are short-lived photos or videos that disappear after 24 hours. Users can post stories, and followers can view them until they expire.

Story Flow:

  1. User uploads a photo or video to their story.
  2. The story is stored in blob storage, and metadata (user ID, timestamp) is stored in the database.
  3. After 24 hours, the story is automatically deleted.

Story Schema:

Field Type Description
story_id String (PK) Unique identifier for the story.
user_id String (FK) ID of the user posting the story.
media_url String URL of the photo/video in blob storage.
timestamp Timestamp Time when the story was posted.
expiration_time Timestamp Time when the story will expire.

6. Search and Explore

Users can search for posts, profiles, and hashtags. The explore section shows trending content based on popularity and user preferences.

Search Flow:

  1. User enters a search query (e.g., a hashtag or username).
  2. The system searches the index for matching posts, users, or hashtags.
  3. Results are ranked by relevance or recency and displayed to the user.

Search Schema:

Field Type Description
search_id String (PK) Unique identifier for the search query.
query String Search query entered by the user.
results Array[String] List of matching post or user IDs.

7. Notifications

The system sends notifications to users when someone likes their post, comments, or follows them.

Notification Flow:

  1. When a user interacts with another user’s post, a notification is generated.
  2. The notification is displayed in the app and optionally sent as a push notification.

Notification Schema:

Field Type Description
notification_id String (PK) Unique identifier for the notification.
user_id String (FK) ID of the user receiving the notification.
type String Type of notification (like, comment, follow).
message String Notification message.
timestamp Timestamp Time when the notification was generated.

Key Challenges

1. Scalability

  • The system must handle millions of users and billions of posts.
    • Solution: Use sharding to partition user data and media across multiple databases and storage services.

2. Real-Time Feed Updates

  • Users expect real-time updates to their feed when someone they follow posts new content.
    • Solution: Use asynchronous messaging systems (e.g., Kafka) to update feeds in real time.

3. High Availability and Low Latency

  • The system must deliver content with minimal delay and remain available 24/7.
    • Solution: Use CDNs for fast content delivery and horizontal scaling for services.

4. Efficient Media Storage and Delivery

  • Storing and delivering millions of photos and videos with minimal latency.
    • Solution: Use blob storage (e.g., AWS S3) and content delivery networks (CDNs) to cache and deliver media.

Advanced Features (Optional)

1. Reels

  • Support for short video content similar to TikTok.
  • Use video compression techniques to optimize file size for mobile streaming.

2. Filters and Effects

  • Allow users to apply filters and effects to their photos and videos before uploading.

3. Content Moderation

  • Use AI-powered tools to detect inappropriate content or spam and flag it for review.

4. Multi-Profile Management

  • Allow users to switch between personal and business accounts from the same app.

Data Flow

1. Uploading a Post

  • The user uploads a photo or video.
  • The media is stored in blob storage, and metadata (caption, user ID, timestamp) is stored in the database.
  • The system updates the feeds of followers with the new post.

2. Viewing the Feed

  • The user opens the app, and the feed service retrieves recent posts from users they follow.
  • The feed is displayed in the app, with posts ordered by time or relevance.

3. Liking and Commenting on a Post

  • The user likes or comments on a post.
  • The system updates the like count and stores the comment in the database.
  • The post owner is notified about the interaction.

Scaling the System

1. Database Sharding

  • Shard user data and post data across multiple databases to distribute load.

2. Content Delivery Network (CDN)

  • Use a CDN to cache and deliver media files (photos, videos, stories) to users around the world with low latency.

3. Caching

  • Use caching for frequently accessed data like popular posts, user profiles, and recent posts.

4. Asynchronous Updates

  • Use message queues (e.g., Kafka) to handle real-time updates to feeds, notifications, and interactions.

Conclusion

Designing an Instagram-like application requires handling real-time interactions, efficient media storage, and personalized content delivery at scale. By leveraging scalable services, CDNs, caching, and sharding techniques, the system can efficiently serve millions of users and billions of posts with low latency and high availability.

Further Reading