Note: - This is a sample SRS document made in attempt to simulate the software design process

System Requirements Document

• This document presents a comprehensive outline of the functional requirements essential for the development and operation of a URL shortening service. The document focuses on delineating core functionalities encompassing URL shortening, redirection mechanisms, and the provision of optional advanced features.

• The document embodies a systematic approach to defining the functional scope and intricacies of a URL shortening service, thereby laying the groundwork for its successful development, deployment, and ongoing refinement in response to evolving user needs and technological advancements.

Introduction

Product :- URL Shortening System (LinkEase)

Product-Scope

• The URL Shortening System aims to streamline the process of creating shortened URLs while aligning with the overarching business goals of enhancing online accessibility and optimising user experience. This system will facilitate the generation of shortened URLs with customisable features, enabling users to efficiently share and access links across different platforms. The primary objectives include improving link management, increasing click-through rates, and enhancing brand visibility through concise and memorable URLs.

Product-Value

• Our URL Shortening System holds significant importance in the digital landscape by offering a practical solution to the challenges associated with lengthy URLs. It empowers users to share links effectively across various communication channels, thereby enhancing communication, fostering engagement, and driving traffic to target destinations. By simplifying the URL-sharing process, our product adds value by saving users' time and effort, while also promoting brand recognition through branded short links.

Audience

• Digital marketers seeking to optimize their social media and marketing campaigns.

• Website owners and administrators aiming to manage and track the performance of their links.

• Social media influencers and content creators looking to streamline the sharing of content.

• Businesses and organizations aiming to enhance their online presence and brand visibility.

Intended-Use

• Generate shortened URLs for long and cumbersome links.

• Customize shortened URLs with relevant keywords or branding elements.

• Track and analyze link performance metrics such as click-through rates and geographic location of users.

• Manage and organize their portfolio of shortened URLs efficiently.

• Integrate shortened URLs seamlessly into their digital content and communication channels.

System-Requirements

Functional-Requirements

URL Shortening

• User Interface

  • The service shall provide a secure and user-friendly interface (web-based or API) for authorized users to submit long URLs for shortening.

  • The interface should offer clear instructions and intuitive functionalities for both standard URL shortening and custom short identifier creation (optional).

  • The interface should display relevant information to users, such as:

    • The original long URL

    • The generated short identifier (if successful)

    • Options to copy or share the short identifier (if successful)

    • Error messages with clear explanations in case of failures (e.g., invalid URL format, duplicate custom identifier)

  • The interface should enforce input validation rules to prevent users from submitting invalid or malformed URLs.

• URL Validation

  • The service shall implement robust URL validation mechanisms to ensure submitted URLs adhere to the correct format (e.g., following HTTP or HTTPS protocols).

  • Validation checks should include verifying:

    • Proper URL structure (protocol, domain name, path)

    • Valid domain names (resolvable DNS records)

    • Reachable endpoints (using techniques like HTTP HEAD requests)

  • The service should handle potential issues gracefully, such as returning error messages for invalid URLs or offering options to retry with corrected URLs.

• Short Identifier Generation

  • Upon successful URL validation, the service shall generate a unique, cryptographically secure short identifier for the submitted long URL.

  • The short identifier length shall be configurable (default: 7 characters) to balance user convenience with the need for a large namespace to handle a vast number of shortened URLs.

  • The character set for short identifiers shall be alphanumeric and case-insensitive (a-z, A-Z, 0-9) to ensure readability and compatibility across various digital platforms.

  • The service shall employ a collision-resistant hashing algorithm (e.g., SHA-256) to generate short identifiers, minimizing the probability of conflicts between randomly generated codes.

Custom Short Identifiers (Optional)

• User Permissions

  • The service shall implement a user permission system to restrict custom short identifier creation to authorized users or specific user groups.

• Character Set Validation

  • The service shall enforce strict character set validation for custom short identifiers, allowing only alphanumeric characters (a-z, A-Z, 0-9) and hyphens (-) to prevent invalid or malicious codes.

• Minimum Length

  • The service shall mandate a minimum length (e.g., 8 characters) for custom short identifiers to minimize conflicts with randomly generated codes and improve manageability.

• Uniqueness Checks

  • The service shall perform comprehensive checks against existing short identifiers within the database to ensure no duplicate custom short identifiers are created.

• Conflict Resolution

  • The service shall define a conflict resolution strategy in case a desired custom short identifier already exists. This may involve suggesting alternative options or prompting the user to choose a different identifier.

URL Redirection

• 3.1 Redirection Behavior

  • Clicking on a short identifier shall trigger an HTTP redirection response with an appropriate status code. The default behavior should be a 301 Moved Permanently for permanent redirects, indicating the long URL has a new location. Alternatively, a 302 Found status code can be used for temporary redirects.

  • The service should handle scenarios where the original long URL becomes unavailable gracefully. This includes:

    • Returning user-friendly error messages with clear explanations (e.g., "404 Not Found" error for broken links)

    • Potentially offering options to report or update the broken link

Advanced Features (Optional)

• Password Protection

  • The service may offer the functionality to password-protect short identifiers. This feature should allow authorized users to set passwords for specific short identifiers, requiring users to enter the correct password before being redirected to the long URL. Password complexity requirements and secure storage mechanisms are essential for this feature.

• URL Expiration

  • The service can be designed to allow for the expiration of short identifiers after a predefined duration (e.g., one week, one month, or one year). This functionality is beneficial for temporary links or links associated with time-sensitive content. The service shall provide clear expiration notifications to users who have created such short identifiers.

Non-Functional-Requirements

Scalability

• Concurrent Requests

  • The service architecture must be designed to handle a high volume of concurrent requests for both URL shortening and redirection. Here's a breakdown of the target capacity:

    • URL Shortening Requests

      • Aim for the service to accommodate approximately 100 million URL shortening requests per second. This ensures the service can efficiently handle large-scale shortening tasks without bottlenecks.

• Redirection Requests

  • The service should be able to handle roughly 8,000 redirection requests per second. This translates to smooth user experience with minimal delays when clicking on shortened URLs.

• Horizontal Scaling

  • The system design should prioritize horizontal scaling capabilities. This means the ability to add more web servers and database nodes to the infrastructure as traffic demands increase. This approach distributes the load evenly, preventing any single component from becoming overloaded and compromising performance.

• Database Selection

  • The choice of database technology plays a crucial role in scalability. A NoSQL database like Cassandra is highly recommended due to its:

    • High Write Throughput

      • Cassandra is optimized for handling large volumes of write operations efficiently, which is essential for shortening a high number of URLs.

• Distributed Architecture

  • Cassandra's distributed architecture allows for adding more nodes to the cluster as needed, scaling horizontally to meet increasing demands.

• Fault Tolerance

  • Cassandra is inherently fault-tolerant, meaning the service can remain operational even if individual nodes experience failures.

Performance

• Low Latency

  • The service should prioritize minimal latency for both URL shortening and redirection operations. This translates to:

    • Fast Shortening

      • Users should experience minimal delays when submitting URLs for shortening. The service should generate short identifiers and store them in the database quickly.

• Rapid Redirection

  • Clicking on a shortened URL should result in a swift redirection to the original long URL. Users should experience minimal waiting time before being directed to the desired content.

• Caching Strategy

  • Implementing a caching layer (e.g., Memcached) is essential for optimizing performance. Frequently accessed short URL mappings can be stored in the cache, reducing the load on the database and enabling faster redirection responses. The cache should be configured with appropriate eviction policies to ensure data freshness.

• Load Balancing

  • Employing a load balancer helps distribute incoming requests evenly across multiple web servers. This prevents any single server from becoming overloaded and impacting performance during high traffic periods.

Availability

• High Uptime

  • The service should strive for exceptional availability, minimizing downtime and ensuring users can access its functionalities consistently. This translates to a target uptime percentage of at least 99.9% (less than 0.1% downtime).

• Redundancy

  • Implementing redundancy in critical components like web servers and database nodes is crucial for achieving high availability. This means having multiple instances of these components running, so the service remains operational even if one node fails.

• Disaster Recovery Plan

  • A comprehensive disaster recovery plan should be in place to ensure quick recovery from unforeseen events like hardware failures or natural disasters. This plan should outline procedures for restoring data and resuming service operations with minimal disruption.

Security

• Malicious URL Shortening

  • The service must implement robust safeguards to prevent unauthorized users from generating short identifiers for malicious purposes (e.g., phishing attacks). This may involve:

    • Multi-Factor Authentication (MFA)

      • Enforcing MFA for user login adds an extra layer of security, making it more difficult for unauthorized individuals to gain access and potentially generate malicious short URLs.

• CAPTCHA Challenges

  • Implementing CAPTCHA challenges during URL shortening requests can help mitigate automated bot attacks that attempt to generate large numbers of short URLs for malicious purposes.

• Custom URL Creation Restrictions

  • Limiting custom URL creation to authorized users or specific user groups helps prevent unauthorized individuals from creating short URLs that could be used for phishing or other malicious activities.

• Data Security

  • The service must employ robust data security practices to protect sensitive information like long URLs, associated metadata (e.g., creation timestamps, custom short identifiers, password protection details), and user authentication credentials. This includes:

    • Encryption

      • Implementing encryption at rest and in transit for all sensitive data is crucial. This ensures that even if an attacker gains access to the data, it will be unreadable without the decryption key.

• Regular Security Audits

  • Conducting regular security audits helps identify potential vulnerabilities in the system and address them promptly. This proactive approach minimizes the risk of security breaches.

Monitoring and Logging

• Monitoring

  • Implement a comprehensive monitoring and logging system to track system activity, identify potential issues, and troubleshoot problems. This system should monitor key metrics like:

    • System Uptime

      • Track uptime percentage to ensure the service meets the target availability goals.

• Response Times

  • Monitor average response times for URL shortening and redirection requests to identify performance bottlenecks.

• Database Performance

  • Track database metrics like read/write throughput and latency to identify potential database performance issues.

• Cache Hit Rates

  • Monitor the cache hit rate to assess the effectiveness of the caching strategy and identify opportunities for optimization.

• Logging

  • Implement a logging system to record user activity, system events, and potential errors. This data can be used for:

    • Security Audits

      • Analyze logs to identify suspicious activity and potential security threats.

• Troubleshooting

  • Review logs to diagnose issues and identify root causes of problems.

• Auditing

  • Maintain a record of user actions and system events for compliance purposes.

Maintainability

• Modular Design

  • The system architecture should be designed with modularity in mind. This allows for easier maintenance, updates, and future enhancements. Each component should have well-defined functionalities and clear interfaces with other components.

• Code Documentation

  • Implement clear and concise code documentation to facilitate understanding, troubleshooting, and future modifications. This documentation should explain the purpose of different code sections, algorithms used, and any design decisions made.

• Automated Testing

  • Develop a comprehensive suite of automated tests to ensure the functionality and performance of the system. These tests should cover various scenarios, including URL shortening, redirection, error handling, and security aspects. Automated testing helps to catch regressions and ensure the system remains stable during updates.

Disaster Recovery

• Disaster Recovery Plan

  • Develop a comprehensive disaster recovery plan that outlines procedures for recovering from unforeseen events like hardware failures, natural disasters, or security breaches. This plan should address:

    • Data Backups

      • Establish a regular data backup schedule to ensure critical information (long URLs, short identifier mappings, user data) is backed up securely and can be restored in case of a disaster.

• Failover Mechanisms

  • Implement failover mechanisms for critical components like web servers and database nodes. This ensures the service can automatically switch to backup instances if a primary component fails.

• Recovery Procedures

  • Define clear recovery procedures to restore service operations as quickly as possible after a disaster. This includes steps for restoring data, redeploying the system, and testing functionality.

System Design

System Architecture

The service will consist of the following core components, each playing a vital role in the URL shortening and redirection process:

• Web Servers

  • These servers act as the front-end of the service, handling user requests for shortening and redirecting URLs. They will parse user input, interact with the database and cache, and generate the appropriate responses (short identifiers for shortening and redirection URLs).

• Load Balancer

  • This component distributes incoming requests evenly among multiple web servers. This ensures optimal performance by preventing any single server from becoming overloaded during high traffic periods.

• Database

  • A robust database will store critical information about short URLs, including:

    • Long URLs

    • Corresponding short identifiers

    • Creation timestamps

    • User IDs (for custom URLs)

    • Expiration times (if implemented)

    • Password details (for password-protected URLs)

• Cache

  • A caching layer will store frequently accessed short URL mappings to improve performance. This reduces the load on the database by serving frequently redirected URLs without requiring database lookups for every request.

Data Flow

• URL Shortening

  1. The user submits a long URL through the user interface (web-based or API) to a web server.

  2. The web server validates the long URL format (e.g., adhering to HTTP protocol).

  3. If valid, the web server interacts with the database to check if a short identifier already exists for the long URL.

  4. If no existing short identifier is found:

     • The web server generates a unique, cryptographically secure short identifier using a collision-resistant hashing algorithm (e.g., SHA-256).

     • The short identifier length can be configurable (default: 7 characters) for a balance between user convenience and a large namespace.

     • The character set for short identifiers will be alphanumeric and case-insensitive (a-z, A-Z, 0-9) to ensure readability across platforms.

  5. The web server stores the mapping between the long URL and the short identifier in the database.

  6. For optional custom short identifiers:

     • Authorized users can submit a desired custom short identifier along with the long URL.

     • The web server validates the custom short identifier against pre-defined rules (e.g., minimum length, allowed characters).

     • The web server checks for conflicts with existing short identifiers in the database.

     • If valid and no conflicts exist, the custom short identifier and long URL mapping is stored in the database.

  7. The web server returns the generated short identifier to the user.

• URL Redirection

  1. When a user clicks on a short identifier, the request is routed through the load balancer and directed to a web server.

  2. The web server retrieves the corresponding long URL from the cache if it exists (faster response).

  3. If the long URL is not found in the cache:

     • The web server queries the database to retrieve the long URL associated with the short identifier.

     • The retrieved long URL is then stored in the cache for future requests.

  4. The web server issues an HTTP redirection response with an appropriate status code (e.g., 301 Moved Permanently for permanent redirects or 302 Found for temporary redirects) to the long URL.

  5. The user's browser is directed to the original long URL.

Advanced Features

• Password Protection (Optional)

  • Authorized users can set passwords for specific short identifiers.

  • When a user clicks on a password-protected short identifier, an additional authentication step is required.

  • The user needs to enter the correct password before being redirected to the long URL.

• URL Expiration (Optional)

  • The system can be designed to allow for the expiration of short identifiers after a predefined duration.

  • Expired short identifiers will no longer be valid and will result in an error message for users.

Technology Stack Considerations

• Web Servers

  • Technologies like Nginx or Apache can be used for handling user requests and responses efficiently.

• Load Balancer

  • Hardware load balancers or software solutions like HAProxy can be implemented for optimal request distribution.

• Database

  • A NoSQL database like Cassandra is recommended due to its scalability and high write throughput capabilities.

• Cache

  • Memcached is a popular choice for caching frequently accessed short URL mappings to improve performance.

Security Considerations

• Authentication and Authorization

  • Implement mechanisms like user accounts and access control lists to restrict unauthorized access to URL shortening functionalities.

• Input Validation

  • Sanitize and validate all user input to prevent malicious code injection attempts (e.g., SQL injection) that could compromise the system.

• Secure Hashing

  • Store passwords using a strong cryptographic hashing algorithm (e.g., bcrypt) to protect user credentials even if there's a data breach.

• HTTPS Enforcement

  • Enforce HTTPS communication throughout the system to encrypt all data transmission between users, web servers, and the database, safeguarding sensitive information.

• Regular Security Audits

  • Conduct regular security audits to identify and address potential vulnerabilities in the system proactively.

Monitoring and Logging

• Implement a comprehensive monitoring and logging system to track system activity, identify potential issues, and troubleshoot problems.

• Monitor key metrics like system uptime, response times, database performance, and cache hit rates to ensure smooth operation.

• Log user activity, including URL shortening requests, redirection events, and potential errors for security and auditing purposes.

Scalability and Performance Optimization

• The system design allows for horizontal scaling by adding more web servers and database nodes to distribute the load and handle increased traffic efficiently.

• Caching frequently accessed short URL mappings significantly improves performance by reducing database load.

• Utilizing a load balancer ensures requests are distributed evenly, preventing bottlenecks and maintaining optimal performance during high traffic periods.