• This page will go over tools needed to design a system

Functional Requirements:

  1. User Registration and Authentication:
    • Allow users to register and authenticate their accounts securely.
  2. Subscription Management:
    • Enable users to subscribe, upgrade, downgrade, or cancel their subscriptions.
    • Provide options for different subscription plans with varying features, durations, and prices.
    • Handle automated subscription renewals and payment processing.
  3. Content Management:
    • Maintain a catalog of products, services, or digital content available for subscription.
    • Ensure secure and efficient delivery of subscribed content to users.
    • Handle updates to the content catalog.
  4. Billing and Payment:
    • Integrate with a reliable payment gateway for secure payment processing.
    • Generate invoices and receipts for users, including subscription details and payment history.
    • Set up billing cycles and automate payment collection accordingly.
  5. Customer Support:
    • Provide a self-service portal or knowledge base for users to find answers to common queries.
    • Implement a ticketing system to handle user inquiries, requests, and complaints efficiently.
    • Enable communication channels for real-time support, such as email or chat.

Non-Functional Requirements:

  1. Scalability and Performance:
    • Design the system to handle increasing user loads, storage requirements, and concurrent transactions.
    • Ensure quick response times and minimal downtime.
    • Implement caching mechanisms for improved performance.
  2. Security and Privacy:
    • Employ encryption and secure connections (HTTPS) to protect user data.
    • Adhere to relevant regulations (e.g., GDPR) regarding data collection, storage, and sharing.
    • Implement proper access controls and user permissions.
  3. Integration:
    • Provide APIs to allow integration with external systems, third-party apps, or partner platforms.
    • Ensure seamless data flow between the subscription service and other systems.

Back-of-the-Envelope Math:

  • Estimate the number of users: Determine the expected number of users subscribing to the service within a given timeframe (e.g., monthly or yearly).
  • Estimate the storage requirements: Calculate the amount of storage needed to store user profiles, subscription details, content catalog, invoices, and other relevant data.
  • Estimate the transaction volume: Estimate the number of subscription-related transactions (sign-ups, upgrades, cancellations, payments) per user per month.

High level Architecture:

  • Frontend: Develop a user-friendly interface for user registration, subscription management, content browsing, and customer support.
  • Backend: Build a scalable backend system to handle user management, subscription management, billing, content management, and integration with payment gateways and external systems.
  • Database: Use a reliable and scalable database solution to store user data, subscription details, content catalog, and other relevant information.
  • Payment Gateway Integration: Integrate with a secure payment gateway to handle payment processing.
  • APIs: Expose APIs for integration with external systems, allowing seamless data exchange.
  • Security: Implement security measures such as encryption, secure connections, and access controls to protect user data.

Sure! Let’s dive deeper into the architecture of the subscription service and create a diagram to illustrate the components and their interactions:

Architecture Diagram:

                  |   User Interface  |
                  |  (Web/Mobile App)|
             |   Frontend Server       |
             |   Backend API Server    |
              /          |           \
             V           V            V
   +-----------------+ +----+---------+ +--------------------+
   |   User Service  | |   Subscription| |   Content Service   |
   |                 | |   Management  | |                    |
   +-----------------+ +--------------+ +--------------------+
                           |    |
                           V    V
                     |   Billing & Payment |
                     |                    |
                   |  Payment     |
                   |  Gateway     |

                     |     User Interface   |
                     |    (Web/Mobile App)  |
                       |  Frontend Server  |
                       |    Load Balancer  |
                    |                       |
                    V                       V
        +----------------------+  +----------------------+
        |     Web Server 1     |  |     Web Server 2     |
        +----------------------+  +----------------------+
                    |                       |
                    V                       V
        +----------------------+  +----------------------+
        |   Backend API Server |  |   Backend API Server |
        +----------------------+  +----------------------+
                    |                       |
                    V                       V
        +----------------------+  +----------------------+
        |      Database        |  |      Database        |
        +----------------------+  +----------------------+
         /            |            \        |
        V             V             V       V
+----------------+ +----------------+ +------------------+
|   User Service | | Subscription   | |   Content Service|
|                | |  Management    | |                  |
+----------------+ +----------------+ +------------------+
         |               |              |
         V               V              V
+--------------------+ +-------------------+
|   Billing Service  | |   Payment Service |
|                    | |                   |
+--------------------+ +-------------------+
         |                                |
         V                                V
+-----------------------------+ +------------------+
|      Billing Database       | |   Payment Gateway|
|                             | |                  |
+-----------------------------+ +------------------+

Detailed Explanation:

  1. User Interface (Web/Mobile App): This is the front-end that users interact with to access the subscription service. It allows users to register, log in, manage their subscriptions, browse content, and contact customer support.

  2. Frontend Server: The frontend server handles user requests from the user interface and communicates with the backend API server. It may also serve static content and handle client-side rendering if required.

  3. Backend API Server: The backend API server acts as the central point of communication for the entire system. It receives requests from the frontend, processes them, and interacts with different services to fulfill the user’s requirements.

  4. User Service: This service manages user-related operations, such as user registration, authentication, and profile management. It stores user data in the database and handles user-related queries.

  5. Subscription Management: This service is responsible for handling subscription-related operations. It manages different subscription plans, allows users to subscribe, upgrade, downgrade, or cancel their subscriptions, and automates subscription renewals.

  6. Content Service: The content service manages the catalog of products, services, or digital content available for subscription. It ensures secure and efficient delivery of subscribed content to users.

  7. Billing & Payment: This component handles the billing and payment operations. It generates invoices and receipts, sets up billing cycles, and automates payment collection using the integration with the payment gateway.

  8. Payment Gateway: The payment gateway is a third-party service that securely processes payments made by users. It handles credit card transactions, validates payments, and notifies the system about successful transactions.


  • Users interact with the User Interface to perform various actions.
  • The Frontend Server communicates with the Backend API Server to process user requests.
  • The Backend API Server interacts with different services (User Service, Subscription Management, Content Service, Billing & Payment) based on the user’s actions.
  • The Billing & Payment component communicates with the Payment Gateway to process payments.


Here are some common tools and technologies that can be used for each component in the architecture:

User Interface (Web/Mobile App):

  • Web: HTML, CSS, JavaScript, React, Angular, Vue.js
  • Mobile: Swift (iOS), Kotlin (Android), React Native, Flutter

Frontend Server:

  • Nginx, Apache HTTP Server

Load Balancer:

  • Nginx, HAProxy, AWS Elastic Load Balancer, Azure Load Balancer

Web Servers:

  • Node.js, Apache HTTP Server, Nginx

Backend API Servers:

  • Node.js, Python (with frameworks like Flask or Django), Java (with frameworks like Spring Boot), Ruby (with frameworks like Ruby on Rails)


  • Relational databases: MySQL, PostgreSQL, Oracle, Microsoft SQL Server
  • NoSQL databases: MongoDB, Cassandra, Redis, Elasticsearch

User Service:

  • Node.js, Python, Java, Ruby

Subscription Management:

  • Node.js, Python, Java, Ruby

Content Service:

  • Node.js, Python, Java, Ruby

Billing Service:

  • Node.js, Python, Java, Ruby

Payment Service:

  • Node.js, Python, Java, Ruby

Billing Database:

  • Relational databases: MySQL, PostgreSQL, Oracle, Microsoft SQL Server
  • NoSQL databases: MongoDB, Cassandra, Redis, Elasticsearch

Payment Gateway:

  • Stripe, PayPal, Braintree, Authorize.Net