Social Network Architecture

Social networks have fundamentally changed how billions of people connect, share, and interact online. Building a scalable social platform requires careful consideration of complex technical challenges like handling massive user data, enabling real-time interactions, managing content delivery, and ensuring high availability across global regions.

This article will look at the key architectural components and design decisions needed to build a social network that can support millions of users. We’ll examine core features like news feeds, friend relationships, content storage, and notification systems, along with scalability, performance, and reliability considerations that shape modern social platforms.

The Core Components

A typical social network architecture can be broken down into many key components:

1. Frontend:

2. Backend:

3. Infrastructure:

4. Third-party Integrations:

5. Security:

Architectural Diagram

This diagram provides an overview of the major components and their interactions in a social network system architecture.

graph LR
    subgraph Frontend
        A["User Interface (Web & Mobile App)"]
    end

    subgraph API_Gateway
        B[API Gateway]
    end

    subgraph Backend
        C[User Service]
        D[Feed Service]
        E[Post Service]
        F[Friendship Service]
        G[Messaging Service]
        H[Notification Service]
        I[Search Service]
        J[Media Service]
    end

    subgraph Infrastructure
        Q[Load Balancer]
        R[Kubernetes]
        S[Docker]
    end

    subgraph Databases
        K["Relational DB (SQL)"]
        L["NoSQL DB (MongoDB)"]
        M["Search DB (Elasticsearch)"]
        N["Cache (Redis)"]
        O["Data Warehouse (BigQuery)"]
        P["Media Storage (CDN/S3)"]
    end


    subgraph Third_Party_Integrations
        T["OAuth (Google/Facebook)"]
        U["Payment Gateway (Stripe)"]
        V["Analytics (Google Analytics)"]
    end

    A --> B
    B --> C
    B --> D
    B --> E
    B --> F
    B --> G
    B --> H
    B --> I
    B --> J
    C --> K
    D --> L
    E --> L
    F --> L
    G --> L
    H --> K
    I --> M
    J --> P
    J --> N
    P --> Q
    Q --> R
    R --> S
    C --> T
    E --> U
    H --> V
    D --> N
    F --> K
    G --> O
    A -.-> Q
    C -.-> Q
    D -.-> Q
    E -.-> Q
    F -.-> Q
    G -.-> Q
    H -.-> Q
    I -.-> Q
    J -.-> Q

Data Flow

The data flow architectures shows information moves between different system components. This section examines the critical paths data takes from user interactions to storage, processing, and delivery - including post creation, content distribution, and real-time updates. Understanding these flows is essential for building a responsive and reliable social platform that can handle millions of concurrent users while maintaining data consistency and low latency.

1. User Signup/Authentication

The user registers via the frontend (mobile/web), which makes an API call to the user service to store user details. The user’s session is created using JWT.

sequenceDiagram
    participant User as User (Frontend)
    participant UI as User Interface
    participant API as API Gateway
    participant Auth as Authentication Service
    participant DB as User Database

    User->>UI: Fills Signup/Login Form
    UI->>API: Sends Form Data (Username, Password, etc.)
    API->>Auth: Forward Form Data for Authentication
    Auth->>DB: Check/Store User Credentials
    DB-->>Auth: Returns User Exists/Success or Create New User
    Auth-->>API: Returns Success/Failure with Token (JWT)
    API-->>UI: Send Authentication Token
    UI-->>User: Display Success or Error Message
    User->>UI: Uses Token for Subsequent Requests
    UI->>API: Send Token with API Requests
    API->>Auth: Validates Token for Authentication
    Auth-->>API: Returns Valid/Invalid
    API-->>UI: Grants Access if Valid

2. Posting Content

The user uploads a post with text or media. The frontend sends the request to the post service, which stores the post in the database. The feed service updates the user’s feed and relevant friends’ feeds.

The below diagram captures the complete flow of data and services involved when a user posts content, including media uploads and feed updates.

sequenceDiagram
    participant User as User (Frontend)
    participant UI as User Interface
    participant API as API Gateway
    participant PostService as Post Service
    participant MediaService as Media Service
    participant FeedService as Feed Service
    participant PostDB as Post Database
    participant MediaCDN as Media Storage (CDN)
    participant FeedDB as Feed Database

    User->>UI: Create Post with Text/Media
    UI->>API: Send Post Request (Text/Media)
    API->>PostService: Forward Post Data
    PostService->>PostDB: Store Post Metadata (Text, Timestamp)
    PostService->>MediaService: Send Media Data for Upload
    MediaService->>MediaCDN: Upload Media to CDN
    MediaCDN-->>MediaService: Return Media URL
    MediaService-->>PostService: Return Media URL
    PostService-->>API: Post Created (Post ID, Media URL)
    API-->>UI: Return Success (Post ID, Media URL)
    PostService->>FeedService: Notify Feed Service (New Post)
    FeedService->>FeedDB: Update User's Feed
    FeedService->>FeedDB: Update Friends' Feeds
    FeedDB-->>FeedService: Feeds Updated
    FeedService-->>UI: Feed Updated for User and Friends

3. Real-time Messaging

The user sends a message via WebSocket, which the messaging service handles in real time.

The below sequence demonstrates how real-time messaging works, leveraging WebSocket connections for instant, two-way communication between users. The message queue is optional and can be used to handle high traffic and ensure reliable delivery.

sequenceDiagram
    participant User as User (Frontend)
    participant WebSocket as WebSocket Connection
    participant MessagingService as Messaging Service
    participant MessageQueue as Message Queue (Optional)
    participant Receiver as Receiver (Frontend)
    participant DB as Message Database

    User->>WebSocket: Send Message (Text/Media)
    WebSocket->>MessagingService: Forward Message via WebSocket
    MessagingService->>DB: Store Message in Database
    alt With Message Queue
        MessagingService->>MessageQueue: Add Message to Queue
        MessageQueue->>Receiver: Deliver Message via WebSocket
    else Without Message Queue
        MessagingService->>Receiver: Deliver Message via WebSocket
    end
    DB-->>MessagingService: Acknowledge Message Stored
    MessagingService-->>User: Acknowledge Message Sent
    Receiver-->>User: Message Delivered Notification

Notification

When a user receives a message or interaction on their post, the notification service pushes a notification to the frontend.

The below sequence demonstrates how notifications work in real time for interactions on posts or messages. The notification service is responsible for handling all interactions and delivering notifications to users efficiently.

sequenceDiagram
    participant UserA as User A (Sender)
    participant UI as User A's Frontend (Web/Mobile)
    participant PostService as Post/Message Service
    participant NotificationService as Notification Service
    participant DB as Notification Database
    participant UserB as User B (Receiver)
    participant ReceiverUI as User B's Frontend (Web/Mobile)

    UserA->>UI: Send Message / Interact with Post
    UI->>PostService: Send Interaction (Message/Post Comment/Like)
    PostService->>NotificationService: Notify about Interaction
    NotificationService->>DB: Store Notification in Notification DB
    NotificationService-->>PostService: Notification Stored
    NotificationService->>ReceiverUI: Push Notification to User B
    ReceiverUI-->>UserB: Display Notification in Real Time

Here are additional key data flows within the system:

1. User Profile Management

sequenceDiagram
    participant User as User (Frontend)
    participant APIGateway as API Gateway
    participant UserService as User Service
    participant SQLDB as SQL Database (Profile Info)
    participant CDN as CDN (Media Storage)
    participant FeedService as Feed Service
    participant FriendProfile as Friend's Profile

    User->>User: Submit Profile Changes (e.g., Name, Picture)
    User->>APIGateway: Send Profile Change Request
    APIGateway->>UserService: Forward Request to User Service
    UserService->>SQLDB: Update Profile Info in SQL DB
    alt Media Upload (Profile Picture)
        UserService->>CDN: Upload New Profile Picture to CDN
    end
    SQLDB-->>UserService: Confirm Profile Info Updated
    UserService-->>APIGateway: Respond with Success
    APIGateway-->>User: Confirm Profile Update Success
    par Feed Update
        UserService->>FeedService: Notify Feed Service of Profile Update
    and Friend Profile Update
        UserService->>FriendProfile: Notify Friends of Updated Profile Info
    end

2. Content Moderation

sequenceDiagram
    participant User as User (Frontend)
    participant APIGateway as API Gateway
    participant ModService as Moderation Service
    participant DB as Moderation Database
    participant Content as Content Database (Posts/Comments)
    participant PostUser as Post Owner (User Who Posted Content)
    participant Reporter as Reporting User (User Who Flagged)

    User->>User: Flag Post or Comment
    User->>APIGateway: Send Flag Request
    APIGateway->>ModService: Forward Request to Moderation Service
    ModService->>Content: Fetch Flagged Post/Comment for Review
    ModService->>ModService: Evaluate Content (AI or Manual Review)
    alt Content Flagged as Inappropriate
        ModService->>DB: Flag Content in Moderation Database
        ModService->>Content: Hide or Remove Flagged Content
        ModService->>PostUser: Send Notification to Content Owner
        ModService->>Reporter: Send Notification to Reporting User
    else Content is Safe
        ModService->>Reporter: Send Notification to Reporting User (No Violation)
    end

3. Search and Discovery

sequenceDiagram
    participant User as User (Frontend)
    participant APIGateway as API Gateway
    participant SearchService as Search Service
    participant SearchDB as Search Database (e.g., Elasticsearch)
    participant ContentDB as Content Database (Posts/Users/Groups)

    User->>User: Enter Search Query (Content, Friends, Groups)
    User->>APIGateway: Send Search Request
    APIGateway->>SearchService: Forward Search Request to Search Service
    SearchService->>SearchDB: Query Search Database (Full-Text Search)
    SearchDB-->>SearchService: Return Search Results (Posts/Users/Groups)
    SearchService-->>APIGateway: Send Search Results to API Gateway
    APIGateway-->>User: Return Search Results to Frontend
    User->>User: Display Search Results (Content, Friends, Groups)

4. Friendship Management

5. Likes, Comments, and Reactions

6. Media Upload and Streaming

sequenceDiagram
    participant U as User
    participant F as Frontend
    participant AG as API Gateway
    participant MS as Media Service
    participant CDN
    participant DB as Post Database

    %% Upload Flow
    U->>F: Upload media (photo/video)
    F->>AG: Send media data
    AG->>MS: Forward media data
    MS->>CDN: Upload media
    CDN-->>MS: Return CDN URL
    MS->>DB: Store media metadata
    DB-->>MS: Confirm storage
    MS-->>AG: Return success
    AG-->>F: Return success
    F-->>U: Show upload confirmation

    %% Playback Flow
    U->>F: Request media playback
    F->>AG: Get media URL
    AG->>MS: Fetch media metadata
    MS->>DB: Query media data
    DB-->>MS: Return metadata
    MS-->>AG: Return CDN URL
    AG-->>F: Return media URL
    F->>CDN: Stream media
    CDN-->>U: Direct media stream

7. Analytics and Logging

8. User Privacy and Security

9. Group or Event Management

10. Push Notifications

These data flows represent various interactions and processes within a typical social network architecture, where different services collaborate to provide a seamless experience for users.

High level Database Entity Diagram

erDiagram
    Users ||--o{ Posts : creates
    Users ||--o{ Comments : writes
    Users ||--o{ Likes : gives
    Users ||--o{ Messages : sends
    Users ||--o{ Friendships : "participates in"
    Users ||--o{ Notifications : receives
    Users ||--o{ Media : uploads

    Users {
        uuid id PK
        string email
        string password_hash
        string full_name
        string profile_pic_url
        datetime created_at
        boolean is_verified
        json settings
        string oauth_provider
        string oauth_id
    }

    Posts {
        uuid id PK
        uuid user_id FK
        string content
        datetime created_at
        array media_urls
        json metadata
        int view_count
        boolean is_public
    }

    Comments {
        uuid id PK
        uuid post_id FK
        uuid user_id FK
        string content
        datetime created_at
        uuid parent_id FK
    }

    Likes {
        uuid id PK
        uuid user_id FK
        uuid post_id FK
        datetime created_at
        string reaction_type
    }

    Messages {
        uuid id PK
        uuid sender_id FK
        uuid receiver_id FK
        string content
        datetime sent_at
        boolean is_read
        array attachments
    }

    Friendships {
        uuid id PK
        uuid user_id1 FK
        uuid user_id2 FK
        string status
        datetime created_at
        datetime updated_at
    }

    Notifications {
        uuid id PK
        uuid user_id FK
        string type
        json payload
        datetime created_at
        boolean is_read
    }

    Media {
        uuid id PK
        uuid user_id FK
        string url
        string type
        int size
        string status
        json metadata
        datetime uploaded_at
    }

    Posts ||--o{ Comments : has
    Posts ||--o{ Likes : receives
    Posts ||--o{ Media : contains

Key aspects of the ERD:

  1. Uses UUID for distributed system scalability
  2. Implements soft deletion and timestamps for data tracking
  3. Stores JSON metadata for flexibility
  4. Includes OAuth integration fields
  5. Uses array types for media and attachments
  6. Maintains referential integrity with foreign keys

Search Engine of Social Network

graph TB
    subgraph Client Layer
        A[Web/Mobile Client]
        B[Search UI Component]
    end

    subgraph API Layer
        C[API Gateway]
        D[Search Service]
        E[Rate Limiter]
    end

    subgraph Search Core
        F[Elasticsearch Cluster]
        G[Search Query Builder]
        H[Result Formatter]
        I[Search Analytics]
    end

    subgraph Data Layer
        J[MongoDB - Posts]
        K[PostgreSQL - Users]
        L[Redis Cache]
    end

    subgraph Indexing Pipeline
        M[Data Change Detector]
        N[Index Manager]
        O[Document Processor]
    end

    A -->|Search Request| B
    B -->|API Call| C
    C -->|Forward| D
    D -->|Rate Check| E
    E -->|Query| G
    G -->|Execute| F
    F -->|Raw Results| H
    H -->|Format| D
    D -->|Cache| L
    
    J -->|Changes| M
    K -->|Changes| M
    M -->|Notify| N
    N -->|Process| O
    O -->|Update| F
    
    D -->|Log| I
    I -->|Improve| G

    classDef service fill:#f9f,stroke:#333
    classDef database fill:#69b,stroke:#333
    classDef pipeline fill:#ffb,stroke:#333
    
    class D,G,H service
    class F,J,K,L database
    class M,N,O pipeline

The diagram shows the flow of data:

  1. Search request starts at the Client Layer
  2. Flows through the API Layer with rate limiting
  3. Gets processed in the Search Core
  4. Results are formatted and returned
  5. Meanwhile, the Indexing Pipeline ensures data stays fresh

The arrows in the diagram show:

The color coding indicates: - Services (pink fill) - Databases (blue fill) - Pipeline components (yellow fill) Lets understand the diagram by breaking it down into its main layers and components:

This architecture provides:

The design prioritizes both search relevance and system performance while maintaining data consistency across the platform.

Scalability & Performance:

4. High Availability & Fault Tolerance: