System requirements

Functional:

1. User Registration and Authentication: Users should be able to sign up and log in to the platform.
2. Coupon Code Retrieval: The service must automatically find and apply coupon codes during checkout.
3. Price Comparison: The system should enable users to compare prices across various online retailers.
4. Deal Alerts: Users should have the option to set alerts for specific products or categories for deals and coupons.
5. Rewards Program: The service should offer a rewards program to encourage user engagement, allowing users to earn points for using the service.
6. User Profile Management: Users must be able to manage their profiles, preferences, and notification settings.

Non-Functional:

1. Performance: The system should handle at least 10,000 concurrent users during peak times without significant performance degradation.
2. Scalability: The architecture should be scalable to support a growing number of users and transactions.
3. Security: User data must be secured using encryption techniques, especially sensitive information such as passwords.
4. Usability: The interface should be user-friendly, ensuring users can easily find and apply coupons.
5. Availability: The system should maintain an uptime of 99.9% to ensure users can access it whenever they need.

Capacity estimation

Capacity estimation is indeed critical for ensuring that an Online Coupon Service can handle expected user load and operate efficiently under various conditions. Here’s how you can approach capacity estimation, including considerations for traffic, user growth, and system requirements.

Capacity Estimation Components

1. User Traffic Estimation

• Concurrent Users: Estimate the peak number of concurrent users accessing the platform. For example:
• If you anticipate 100,000 users might access the service during peak shopping hours, estimating that around 5% will be concurrent gives you about 5,000 concurrent users.
• Requests per Second (RPS): Assess the average number of requests each user will make:
• If each user makes around 3 requests per session, and sessions average about 10 minutes, then:
• ( RPS = \frac{(100,000 users) \times (3 requests)}{(10 min \times 60 sec)} \approx 500 requests/second )

2. Data Storage Requirements

• User Data: Estimate the storage space needed for user profiles:
• For 100,000 users with an average profile size of about 1KB, the required storage would be:
• ( 100,000 users \times 1KB \approx 100 MB )
• Coupon Data: For coupon storage, if you estimate having 50,000 active coupons with an average size of 2KB:
• ( 50,000 coupons \times 2KB \approx 100 MB )

3. Database Load

• Read vs. Write Operations: Estimate the read/write operations:
• If user profiles are updated rarely but coupons are frequently queried, assume a read/write ratio of 80% reads to 20% writes for the database.

API design

Based on these functionalities, we can define the following core APIs:

User Management APIs

• User Registration:
• POST /users
• Parameters: user details (name, email, password, etc.)
• User Login:
• POST /auth/login
• Parameters: credentials (email, password)
• Returns: authentication token
• User Profile Update:
• PUT /users/{userId}
• Parameters: updated user details
• User Preferences Update:
• PUT /users/{userId}/preferences
• Parameters: updated user preferences (e.g., categories, brands)

Coupon Management APIs

• Coupon Retrieval:
• GET /coupons?storeId={storeId}&productId={productId}
• Returns: list of applicable coupons
• Coupon Application:
• POST /coupons/apply
• Parameters: coupon code, order details
• Returns: updated order total
• Coupon Validation:
• POST /coupons/validate
• Parameters: coupon code, order details
• Returns: validation status

Price Comparison APIs

• Product Search:
• GET /products?query={query}
• Returns: list of products with prices from different retailers
• Price History:
• GET /products/{productId}/priceHistory
• Returns: price history for a product

Deal Alerts APIs

• Subscribe to Alerts:
• POST /alerts/subscribe
• Parameters: user ID, product/category preferences
• Unsubscribe from Alerts:
• DELETE /alerts/unsubscribe
• Parameters: user ID, alert ID

Rewards Program APIs

• Earn Points:
• POST /rewards/earn
• Parameters: user ID, action (e.g., coupon applied, purchase made)
• Redeem Rewards:
• POST /rewards/redeem
• Parameters: user ID, reward ID
• Reward Catalog:
• GET /rewards/catalog
• Returns: list of available rewards

Database design

Below is the ER diagram, for the entities.

For the Online Coupon Service, we can utilize different databases based on the data structure requirements and the characteristics highlighted by the CAP theorem. Here are the suggestions:

1. Relational Database (SQL) - PostgreSQL or MySQL

• Entities: Transaction, User
• Database Type: SQL
• Reasoning: Ideal for structured data like user profiles and transactions, where relationships and ACID compliance (Atomicity, Consistency, Isolation, Durability) are important.
• CAP Theorem Focus: Consistency Focused - It provides strong consistency guarantees, making it suitable for transactions.

2. NoSQL Database (Document Store) - MongoDB

• Entities: Reward, Coupon, Store
• Database Type: NoSQL (Document Store)
• Reasoning: Suitable for flexible schema and unstructured data such as coupon details and user preferences, allowing easy scaling.
• CAP Theorem Focus: Availability Focused - It emphasizes availability and partition tolerance, making it well-suited for situations where the service needs to be continuously accessible even during network partitions.

3. In-Memory Database - Redis

• Database Type: NoSQL (In-Memory Key-Value Store)
• Reasoning: Best for caching frequently accessed data, such as the latest coupons and real-time notifications, to improve performance.
• CAP Theorem Focus: Availability Focused - By storing data in memory, it can serve requests very quickly, prioritizing quick access and higher availability over strong consistency in certain scenarios.

When designing the Online Coupon Service, applying partitioning, sharding, and scaling strategies for databases is crucial for enhancing performance, availability, and manageability. Here's how we can approach each aspect for the various database types we've discussed:

1. Partitioning and Sharding

a. Relational Database (PostgreSQL/MySQL)

• Partitioning:
• Vertical Partitioning: Split larger tables into smaller, related tables using a subset of columns (e.g., separating user information from transaction details).
• Horizontal Partitioning: Divide large tables into smaller tables (partitions) based on a specific key, such as user regions (e.g., partitioning users by geographical location).
• Sharding:
• Use a sharding approach to horizontally scale the database across multiple instances based on user ID ranges or geographic locations. This distributes the load and improves read/write performance.

b. NoSQL Document Store (MongoDB)

• Partitioning:
• MongoDB uses sharding natively, allowing automatic horizontal partitioning of data based on a chosen shard key (e.g., user ID or category ID for coupons).
• Sharding:
• Utilize sharding to distribute coupon documents across multiple replica sets, optimizing read/write operations for a large volume of coupons from various retailers.

2. Scaling Strategies

a. Relational Database

• Read Scaling:
• Implement read replicas to offload read traffic from the primary database instance, improving read performance during high-traffic periods.
• Write Scaling:
• Use master-slave replication or database clustering to handle a higher write load. Be mindful of potential latency between the primary and replicas.

b. NoSQL Document Store (MongoDB)

• Horizontal Scaling:
• Leverage auto-sharding capabilities to scale out by adding more shards (instances) as data grows, efficiently handling increased write and read requests.

Indexing Strategies

1. Relational Databases (PostgreSQL/MySQL)

• B-Tree Indexes:
• Default index type in many SQL databases; useful for equality and range queries.
• Consider using B-Tree indexes on columns frequently used in WHERE conditions, such as email in the User table or store_id in the Coupon table.
• Hash Indexes:
• Useful for equality comparisons (e.g., id) but not suitable for range queries.
• Can be applied to user IDs or coupon codes for rapid lookup.
• Composite Indexes:
• Combine multiple columns into a single index (e.g., store_id and expiration_date in the Coupon table) to speed up queries that use both columns for filtering.

2. NoSQL Document Store (MongoDB)

• Single Field Index:
• Create indexes on frequently queried fields (e.g., code in the Coupon collection) to speed up lookups.

Data Retrieval Optimizations

1. Query Optimization: Analyze your queries periodically and optimize them by reducing the number of joined tables or using subqueries effectively.
2. Caching: Utilize caching mechanisms such as Redis or within the application to store results of frequently accessed data, reducing database queries.
3. Lazy Loading: Implement lazy loading for data that is not immediately needed, reducing initial load times and database I/O.
4. Database Connection Pooling: Use connection pooling to minimize the overhead associated with opening and closing database connections, particularly for high-traffic services.
5. Data Denormalization: In NoSQL databases, consider denormalizing data by embedding related documents (e.g., embedding user profiles in transaction documents) to reduce join operations.

High-level design

1. User Interface (UI):
2. A web and mobile application interface to allow users to interact with the service.
3. Feature sections include coupon search, deals, price comparison, user profile, etc.
4. Database: A relational or NoSQL database to store user data, coupon information, product details, and transaction logs.
5. Web Scraper / Data Aggregator: A system to scrape coupon codes from various online retailers and aggregate prices for comparison.
6. Notification Service: A service to send alerts to users about new deals or reward updates.
7. User Service: Handles user registration, authentication, profile management, and preferences.
8. Coupon Service: Manages coupon creation, retrieval, application, and validation.
9. Price Comparison Service: Compares product prices across different retailers.
10. Deal Alert Service: Manages user subscriptions, sends notifications, and tracks deal history.
11. Reward Service: Manages user points, rewards, and redemption.

Request flows

Let's detail the request flow scenario for a user applying a coupon code during an online shopping checkout on your Online Coupon Service. This will illustrate how the various components interact to fulfill the user’s request.

Request Flow Scenario: Applying a Coupon Code

1. User Initiates Checkout: The user selects items for purchase and starts the checkout process on an e-commerce site.
2. Request for Coupons: The user clicks on the browser extension or app to find available coupons.
3. Send Coupon Request: The UI sends a request to the Backend Service to retrieve applicable coupon codes for the items in the user's cart.
4. Backend Service Processing: The Backend Service processes the request, first checking the Database for applicable coupons. If no relevant coupons are found, it sends a request to the Web Scraper to find fresh coupons.
5. Data Retrieval: The Web Scraper collects coupon data from various online retailers and returns it to the Backend Service. The Backend Service stores this new coupon information back in the Database for future reference.
6. Send Coupons to User: The Backend Service sends the list of applicable coupons back to the User Interface.
7. User Applies Coupon: The user selects a coupon from the presented list, which is then applied during the checkout process.
8. Confirmation and Notification: The system confirms the application of the coupon, updates the price, and optionally sends a notification to the user via the Notification Service.

Detailed component design

Let's break down the detailed component design for each major part of the Online Coupon Service, including their responsibilities and interactions.

1. User Interface (UI)

Responsibilities:

• Provide a user-friendly interface on web and mobile platforms.
• Allow users to search for coupons, manage their profiles, and view rewards.
• Display real-time notifications regarding deals and applied coupons.

Components:

• Web Application: Built using frameworks like React or Angular.
• Mobile Application: Native applications for iOS and Android or a hybrid solution using Flutter or React Native.
• Browser Extension: A lightweight extension that logs user activity and provides a quick way to apply coupons during checkout.

2. Backend Service

Responsibilities:

• Handle all business logic related to user requests, including coupon searching and rewards calculation.
• Ensure secure communication and data processing.

Components:

• API Gateway: Manages all incoming requests and routes them to the appropriate services (e.g., Express.js for Node.js).
• Authentication Service: Handles user registration and authentication (using OAuth, JWT, etc.)
• Coupon Management Service: Processes requests for coupon retrieval, validation, and application.
• User Management Service: Manages user profiles, rewards, and settings.

3. Database

Responsibilities:

• Store user data, coupon details, transaction records, and product information securely.

Components:

• Relational Database (like PostgreSQL or MySQL) for structured data (users, transactions).
• NoSQL Database (like MongoDB) for flexible schema data like coupons from different retailers.

4. Web Scraper / Data Aggregator

Responsibilities:

• Periodically scrape data from various e-commerce websites to gather coupon codes and pricing information.

Components:

• Scraping Engine: A service using libraries like BeautifulSoup (Python) or Puppeteer (Node.js).
• Scheduler: A cron job or service that triggers scraping at defined intervals.
• Data Processing Pipeline: Validate and normalize scraped data before storing it in the database.

5. Notification Service

Responsibilities:

• Deliver real-time updates and alerts to users about new deals, coupons, or rewards.

Components:

• WebSockets: Real-time communication protocol for sending live updates to the UI.
• Email/SMS Service: For sending non-instantaneous notifications (using services like SendGrid or Twilio).
• Notification Queue: A message queue (e.g., RabbitMQ or AWS SQS) to manage and buffer notifications.

Detailed Component Interaction Diagram

Now, let’s visualize these interactions within the overall architecture:

Coupon Discovery Logic

Enhancing the Coupon Discovery Logic is key to improving user experience on your Online Coupon Service. Here’s a deep dive into how you can implement a more sophisticated coupon discovery process, incorporating machine learning and collaborative filtering.

Suggestions for Improving Coupon Discovery Logic

1. Personalized Recommendations

• User Behavior Analysis:
• Track user interactions and preferences, such as items they frequently view, purchase history, and types of coupons they use. This data can be leveraged to create personalized coupon recommendations.
• Machine Learning Models:
• Utilize algorithms like Collaborative Filtering or Content-Based Filtering to predict which coupons are most likely to interest a user based on historical data.
• Example: Train a model on user behavior data to identify patterns and suggest coupons that similar users utilized successfully.

2. Collaborative Filtering

• User-Based Collaborative Filtering:
• This method recommends coupons based on similarities between users. If User A and User B have similar shopping behaviors, coupons used by User B can be suggested to User A.
• Item-Based Collaborative Filtering:
• Compare items instead of users. If a user frequently purchases items that have associated coupons, suggest those coupons to them.
• Implementation:
• Use Matrix Factorization techniques (like SVD) or neighborhood methods (k-nearest neighbors) to generate these correlations efficiently.

3. Enhanced Search Capabilities

• Keyword Matching:
• Implement a robust search mechanism that allows users to enter keywords related to products. Coupons related to those keywords can be surfaced dynamically through indexing.

4. Contextual Recommendations

• Location-Based Recommendations:
• Leverage geolocation data to recommend coupons based on the user's location, tailoring deals from nearby stores or offer time-sensitive discounts.

Trade offs/Tech choices

It's crucial to address trade-offs in technology choices when designing a system like an Online Coupon Service, as various aspects such as performance, scalability, maintainability, and cost must be considered. Here's how you can present your understanding of trade-offs for different technology choices associated with the components of the system:

Key Technology Choices and Associated Trade-offs

1. Database Choice: SQL vs. NoSQL

• SQL (e.g., PostgreSQL)
• Pros:
• Strong consistency guarantees due to ACID compliance.
• Complex queries are easier to handle with JOINs, making relational data management straightforward.
• Cons:
• May not scale horizontally as easily as NoSQL databases, potentially leading to performance bottlenecks with high-write loads.
• Schema rigidity can be a limitation as data requirements evolve over time.
• NoSQL (e.g., MongoDB, Cassandra)
• Pros:
• High scalability as they are designed to distribute data across multiple nodes effortlessly.
• Schemaless design allows for flexibility in handling diverse data formats, which is beneficial for dynamic coupon data.
• Cons:
• Usually prioritize availability and partition tolerance over consistency, which can lead to stale reads in certain situations.
• Complex querying can become challenging due to the lack of JOIN operations.

2. Caching Strategy: In-Memory Databases (Redis) vs. No Cache

• Using Redis for Caching
• Pros:
• Dramatically improves read performance by storing frequently accessed data in memory.
• Reduces load on the primary database, allowing it to focus on write operations.
• Cons:
• The additional complexity of maintaining cache coherence (ensuring the cache is up-to-date) introduces challenges.
• Data in Redis is volatile, leading to potential data loss between cache lifetimes; must consider persistence options.
• No Caching
• Pros:
• Simplicity in architecture and data retrieval logic, avoiding issues associated with cache coherence.
• Cons:
• Increased load on the database may lead to performance bottlenecks, especially during peak usage periods.

Failure scenarios/bottlenecks

1. Database Failure
2. Scenario: Primary database becomes unavailable due to hardware failure or network issues.
3. Mitigation: Implement a high-availability architecture with master-slave replication and failover mechanisms to ensure that secondary databases can take over automatically if the primary fails.
4. Service Outage
5. Scenario: Increased traffic leads to service overload, resulting in downtime or slow response times.
6. Mitigation: Implement load balancing and use an auto-scaling strategy to allocate resources dynamically based on demand. Additionally, consider adding caching layers to decrease pressure on backend services.
7. Data Loss
8. Scenario: Corruption of data or accidental deletion in database storage.
9. Mitigation: Implement regular backup strategies, utilizing point-in-time recovery methods and employing database replication to ensure data persistence across multiple geographic locations.

Future improvements

Here are some potential future improvements that can be considered for the Online Coupon Service, focusing on enhancing user experience, increasing operational efficiency, and expanding market reach:

1. Advanced Personalization

• Recommendation Engine Enhancements: Implement sophisticated algorithms, such as deep learning models, to provide more accurate and personalized coupon recommendations based on user behavior, preferences, and contextual information.

2. Social Media Integration

• User Engagement Features: Introduce social sharing functionalities, allowing users to share deals on social platforms. This can foster community involvement and drive organic traffic to the service.

3. Mobile Application Development

• Dedicated Mobile App: Develop a mobile application for both Android and iOS that facilitates on-the-go coupon discovery, browsing, and applying coupons directly at checkout.

4. Enhanced Analytics Dashboard

• Merchant Analytics: Create an analytics dashboard for partnered retailers to gain insights into coupon performance, user engagement rates, and ROI on promotions, helping them optimize their strategies.