FlyrTech - Technical Challenge

A .NET 8 solution with an intentional race condition for you to analyze and fix.

📋 Challenge Overview

This is a 3-5 hour technical assessment with two main components.

💡 IMPORTANT: We care more about how you think about the problem and your solution design than the implementation itself. We want to see your analytical process, how you evaluate trade-offs, and how you communicate your design decisions.

Part 1: Technical Analysis (3-4 hours)

Complete the TECHNICAL_ANALYSIS.md document with your in-depth analysis of the race condition problem and proposed solutions.

Part 2: Implementation (45-60 minutes)

Implement one of your proposed solutions to fix the race condition in JourneyService.UpdateSegmentStatusAsync().

🚀 Getting Started

1. Fork this repository to your own GitHub account:

• Click the "Fork" button at the top right of this repository
• Clone your forked repository to your local machine:

git clone https://github.com/YOUR_USERNAME/FlyrTechnicalTest.git
cd FlyrTechnicalTest

2. Read the full challenge details: See RACE_CONDITION_CHALLENGE.md for the complete problem description.

2. Start Redis:

docker run -d -p 6379:6379 --name redis-flyrtech redis:latest

3. Verify the problem exists:

dotnet test --filter "FullyQualifiedName~UpdateSegmentStatus_With20ConcurrentUpdates"

Expected: ❌ TEST FAILS - Updates are lost due to race condition

4. Complete your technical analysis: Fill out TECHNICAL_ANALYSIS.md with your analysis and proposed solutions.

5. Implement your solution: Fix the code to make all tests pass.

6. Verify your solution works:

dotnet test

Expected: ✅ ALL 23 tests pass

7. Commit and push your changes:

git add .
git commit -m "Fix race condition in JourneyService"
git push origin main

📊 Deliverables

Submit your work by sending us the link to your forked repository.

Your repository should include:

1. TECHNICAL_ANALYSIS.md - Completed with your detailed analysis
2. Code changes - Your implementation to fix the race condition
3. All tests passing - Including the concurrent updates test
4. Clean commit history - Well-organized commits with clear messages

---

Solution Structure

FlyrTech/
├── FlyrTech.Core/                  # Domain layer
│   ├── ICacheService.cs            # Cache interface
│   ├── IJourneyService.cs          # Journey interface
│   └── Models/Journey.cs           # Domain model
├── FlyrTech.Infrastructure/        # Infrastructure
│   ├── RedisCacheService.cs        # Redis implementation
│   └── JourneyService.cs           # ⚠️ Has race condition
├── FlyrTech.Api/                   # Web API
│   ├── Program.cs                  # DI & initialization
│   └── Data/journeys.json          # Sample data
└── FlyrTech.Tests/                 # Tests
    └── JourneyRaceConditionTests.cs # Demonstrates problem

Prerequisites

• .NET 8 SDK - Download
• Redis - See installation below

Redis Installation

Windows (Docker - Recommended)

# Install Docker Desktop: https://www.docker.com/products/docker-desktop
docker run -d -p 6379:6379 --name redis-flyrtech redis:latest

# Verify
docker ps
redis-cli ping  # Should respond: PONG

Windows (WSL2)

wsl --install
# Inside WSL:
sudo apt update && sudo apt install redis-server
sudo service redis-server start
redis-cli ping

macOS

brew install redis
brew services start redis
redis-cli ping

Linux (Ubuntu/Debian)

sudo apt update && sudo apt install redis-server
sudo systemctl start redis-server
redis-cli ping

Building & Running

Build:

dotnet build FlyrTech.sln

Run Tests:

dotnet test FlyrTech.Tests/FlyrTech.Tests.csproj

Expected Results:

• ✅ 22 tests pass
• ❌ 1 test fails (race condition demo)

Run API:

cd FlyrTech.Api
dotnet run

• Swagger UI: https://localhost:5001/swagger
• On startup, loads 3 journeys into cache

API Endpoints

Journeys

GET /api/journeys - List all journey IDs

GET /api/journeys/{id} - Get journey details

PUT /api/journeys/{id}/segments/{segmentId}/status - Update segment (⚠️ race condition)

{ "status": "Departed" }

PUT /api/journeys/{id}/status - Update journey status

{ "status": "InProgress" }

Cache

GET /api/cache/demo - Demo endpoint with 60s TTL

GET /api/cache/{key} - Get value

POST /api/cache/{key} - Set value

DELETE /api/cache/{key} - Remove value

Testing Strategy

All tests require running Redis on localhost:6379.

Test Categories:

1. RedisCacheServiceTests (21 tests) - Cache operations
2. CacheEndpointTests (1 test) - API behavior
3. JourneyRaceConditionTests (2 tests):
   • ❌ UpdateSegmentStatus_With20ConcurrentUpdates - FAILS (intentional)
   • ✅ UpdateSegmentStatus_SequentialUpdates - PASSES

Configuration

FlyrTech.Api/appsettings.json:

{
  "Redis": {
    "ConnectionString": "localhost:6379"
  }
}

For remote Redis:

{
  "Redis": {
    "ConnectionString": "host:port,password=secret"
  }
}

Architecture

Clean Architecture with DI:

• ICacheService → RedisCacheService (Singleton)
• IJourneyService → JourneyService (Singleton)
• IConnectionMultiplexer → Redis connection pool (Singleton)

Data Flow:

1. API starts → Loads Data/journeys.json
2. Initializes Redis cache with 3 journeys
3. Endpoints use IJourneyService
4. Service uses ICacheService (Redis)

Troubleshooting

Redis Connection Error:

RedisConnectionException: It was not possible to connect...

Solutions:

1. Check Redis is running: redis-cli ping → PONG
2. Check port: netstat -an | findstr "6379" (Windows) or grep 6379 (Unix)
3. Docker status: docker ps and docker logs redis-flyrtech
4. Clear data: redis-cli FLUSHALL

Tests Failing Unexpectedly:

1. Ensure Redis is running
2. Clear Redis: redis-cli FLUSHALL
3. Restart Redis service
4. Check logs

📚 Additional Documentation

• RACE_CONDITION_CHALLENGE.md - Detailed problem description and success criteria
• TECHNICAL_ANALYSIS.md - Template for your technical analysis (to be completed)

Key Features

✅ Real Redis integration (not mocked)
✅ Race condition demonstration for learning
✅ Clean architecture & DI
✅ Journey data auto-initialization
✅ 23 tests (22 pass, 1 intentional fail before fix)
✅ Swagger documentation
✅ Async/await patterns

License

MIT