Final Exam

Overview

• Course: Advanced Microservices Architecture
• Duration: 180 minutes
• Passing Score: 70.0%
• Total Points: 100.0

Description

You have been hired as a Lead Backend Engineer for 'FinFlow', a fintech startup. Your task is to build a high-performance transaction processing system. The system requires an API Gateway, a Transaction Service, and a Fraud Detection Service. You must implement secure access, asynchronous messaging for decoupling, and a Saga pattern to handle distributed consistency. You have 180 minutes to complete the implementation.

Prerequisites

• Python 3.10+
• Docker & Docker Compose installed
• Experience with FastAPI and Pydantic
• Knowledge of RabbitMQ or Kafka
• Knowledge of Redis

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Tasks

Task 1: Secure API Gateway Implementation

Time: 0.75 hours

Initialize the project structure and create a centralized API Gateway using FastAPI. This gateway will serve as the single entry point for all client requests.

Requirements:

• Create a FastAPI application acting as the API Gateway.
• Implement a 'Reverse Proxy' mechanism that routes requests to downstream services (Transaction Service and Fraud Service) based on path prefixes (e.g., /api/v1/transactions).
• Implement JWT Authentication middleware at the Gateway level. Requests without a valid token should be rejected with HTTP 401.
• Create a mock 'Auth Service' endpoint within the Gateway (or separate) to issue tokens for testing.

Deliverables:

• gateway_service/ directory
• JWT verification logic
• Proxy routing logic

Hints:

• Use httpx for async proxying within FastAPI.
• Keep the secret key in an environment variable.

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Task 2: Async Communication & Service Decoupling

Time: 1.0 hours

Implement the core Transaction Service and Fraud Detection Service. Use an event-driven approach to decouple the transaction creation from the fraud check.

Requirements:

• Create the 'Transaction Service' (FastAPI). It should accept a POST /transactions request, save the transaction with status 'PENDING' to a local database (SQLite/Postgres), and immediately return a 202 Accepted response.
• Upon saving, publish a 'transaction_created' event to a Message Broker (RabbitMQ).
• Create the 'Fraud Service'. It must consume the 'transaction_created' event.
• The Fraud Service should contain logic to approve (amount < 10000) or reject (amount >= 10000) the transaction.

Deliverables:

• transaction_service/ directory
• fraud_service/ directory
• RabbitMQ producer/consumer implementation

Hints:

• Use Pydantic models to validate the message payload.
• Ensure the consumer runs as a background task or separate process.

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Task 3: Distributed Transactions (Saga Pattern)

Time: 0.75 hours

Implement a Choreography-based Saga pattern to ensure data consistency across services.

Requirements:

• Modify the Fraud Service: After processing, it must publish a result event ('fraud_check_passed' or 'fraud_check_failed').
• Update the Transaction Service to consume these result events.
• If 'fraud_check_passed' is received, update the local transaction status to 'CONFIRMED'.
• If 'fraud_check_failed' is received, update the local transaction status to 'REJECTED'.
• Ensure idempotency: processing the same event twice should not corrupt the state.

Deliverables:

• Updated consumer logic in Transaction Service
• Updated producer logic in Fraud Service

Hints:

• Include the transaction_id in all messages to correlate events.

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Task 4: Performance & Observability

Time: 0.5 hours

Enhance the system with caching and basic observability to monitor health and performance.

Requirements:

• Implement Redis caching in the Transaction Service for GET /transactions/{id} endpoints. Cache TTL should be 60 seconds.
• Add a structured logger to all services that includes the correlation_id (passed from the Gateway) in every log entry.
• Expose a standard /health endpoint in all services that checks database and broker connectivity.

Deliverables:

• Redis integration code
• Middleware for correlation ID extraction/logging
• Health check endpoints

Hints:

• Use Python's logging library with a custom formatter or structlog.

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Submission Rules

• All code must be submitted in a single Git repository.
• Include a docker-compose.yml file that orchestrates the Gateway, Transaction Service, Fraud Service, RabbitMQ, and Redis.
• Include a README.md with instructions on how to build, run, and test the endpoints using cURL or Postman.
• Ensure all dependencies are listed in requirements.txt or pyproject.toml for each service.

Grading Rubrics

Criterion	Weight	Excellent	Good	Satisfactory	Needs Improvement
Architecture & Microservices Patterns	35.0%	Clear separation of concerns; correct implementation of API Gateway; seamless async communication; robust Saga pattern implementation.	Services are separated but logic may leak between layers; Async communication works but lacks robustness; Saga pattern works for happy path only.	Monolithic structure disguised as microservices; synchronous communication used where async was required.	Failed to implement microservices architecture; direct database access between services.
Functionality & Correctness	35.0%	All endpoints work as specified; Security is enforced; Saga compensates correctly on failure; Cache hits/misses work as expected.	Core flows work; some edge cases in the Saga pattern fail; Security is present but permissive.	Basic CRUD works; Async messaging is flaky or incomplete; Caching is missing.	Code does not run or major features are missing.
Code Quality & Standards	20.0%	PEP8 compliant; Type hinting used throughout; Effective error handling; Clean project structure.	Readable code; some typing missing; minor linting errors; adequate error handling.	Messy code structure; no type hinting; minimal error handling (lots of bare excepts).	Unreadable code; no modularity.
DevOps & Deliverables	10.0%	Docker Compose brings up the whole stack with one command; README is comprehensive.	Docker configuration requires minor manual tweaks; README is brief.	Missing Docker files; manual startup of 5 terminals required.	No build instructions provided.