Q&A Platform

*This project is part of Aalto University's Designing and Building Scalable Web Applications course (completed in spring 2024).

This project is a Question and Answer web application designed for coursework discussions. It allows users to:

• View courses and post questions related to those courses
• Provide answers (including LLM-generated answers)
• Upvote questions and answers to surface the most helpful content
• Cache frequently accessed data for improved performance

The system demonstrates scalability and best practices, integrating multiple services, caching, end-to-end testing, and performance testing.

Features

1. Database

   • Uses PostgreSQL for structured data storage (courses, questions, answers, likes).
   • Flyway manages schema migrations under flyway/sql.

2. Caching

   • Incorporates Redis to cache frequent queries (like listing questions/answers).
   • Utilizes separate Redis databases:
     • DB 0: Caches question and answer data.
     • DB 1: Manages rate-limiting keys to enforce user posting limits.
   • Flushing strategies ensure data remains fresh when new questions or answers are added without affecting rate limits.

3. End-to-End Tests

   • Uses Playwright to confirm the UI flows (home page, course page, question page) function correctly.
   • Tests are located in e2e-playwright/tests.

4. Performance Tests

   • Leverages k6 scripts in the k6/ folder to measure and optimize performance under various load scenarios.

5. User Interactions

   • Upvoting logic for questions and answers via join tables in the database (questionLike, answerLike).

6. Styling & Framework

   • The UI is built with Astro, Svelte, and TailwindCSS for a modern, efficient front-end.
   • The back-end uses Deno for the qa-api service, with a focus on simplicity and performance.

7. Rate Limiting

   • Enforces that a single user (identified by userUuid) can post at most one question and one answer per minute.
   • Implemented using a separate Redis database to manage rate-limiting without interfering with cached data.

8. Separate Configurations for Development and Production

   • Docker setups (docker-compose.yml for dev, docker-compose.prod.yml for production) to demonstrate how the app scales in different environments.

Project Structure

A brief overview of the main directories (subject to change as the project evolves):

├── e2e-playwright
│   └── tests/                  # End-to-end tests (Playwright)
├── flyway
│   └── sql/                    # Database migration scripts (Flyway)
├── k6                          # Performance testing scripts (k6)
├── llm-api                     # LLM API client for generating answers
├── nginx                       # NGINX configuration for routing
├── qa-api
│   ├── controllers             # API controllers for courses, questions, answers, users
│   ├── database                # PostgreSQL interactions for Deno
│   ├── services                # Business logic (caching, LLM calls, etc.)
│   └── util                    # Utility functions (cache proxies, etc.)
├── qa-ui                       # User interface (Astro, Svelte and Tailwind)
├── redis                       # Redis configuration (redis.conf)
├── docker-compose.prod.yml     # Production Docker Compose setup
├── docker-compose.yml          # Development Docker Compose setup
├── DATABASE.md                 # Database schema and caching strategy
├── PERFORMANCE_TEST_RESULTS.md # Performance testing results
├── REFLECTION.md               # Key design decisions and potential improvements
├── RUNNING.md                  # Deployment and testing instructions
└── README.md                   # This file

Deployment and Testing

For details on deploying the application locally, along with instructions for running the end-to-end tests and performance tests, see RUNNING.md. This file outlines:

• How to run the application in development mode with Docker Compose,
• How to migrate and start the system in production mode,
• How to invoke Playwright E2E tests in Docker,
• How to launch k6 performance tests.

My performance testing results can be found in PERFORMANCE.md.

Database Schema

A short discussion of the applications database schema and caching strategy can be found in DATABASE.md.

Reflection

A short discussion of the application’s key design decisions (e.g., normalized database schema, caching approach, LLM integration) and potential improvements for performance can be found in REFLECTION.md.