Fastapi-test-task

Wallet Service API

Overview

RESTful API service for managing digital wallets with support for deposits and withdrawals.

Features

• Async PostgreSQL with connection pooling
• Concurrent transaction safety with row-level locking
• Automatic retry mechanism
• Transaction monitoring and logging
• Database migrations with Liquibase
• Comprehensive test coverage with async testing
• Decimal precision for financial operations
• Input validation and error handling

Technical Details

• FastAPI framework for high performance
• SQLAlchemy with async support and row-level locking
• PgBouncer for connection pooling in transaction mode
• Pydantic for data validation
• Liquibase for database versioning
• PostgreSQL for ACID compliance
• Docker for containerization
• pytest-asyncio for async testing

API Endpoints

• POST /api/v1/wallets/ - Create new wallet
• GET /api/v1/wallets/{wallet_id} - Get wallet info
• POST /api/v1/wallets/{wallet_id}/operation - Process deposit/withdrawal

Quick Start

1. Clone repository
2. Copy .env.example to .env
3. Run docker-compose up -d
4. API available at http://localhost:8000

Testing

Run tests with coverage report:

# Run all tests with coverage
docker-compose exec app pytest tests/ -v --cov=app --cov-report=term-missing
# Run specific test file
docker-compose exec app pytest tests/test_wallets.py -v
# Run tests with specific marker
docker-compose exec app pytest -m "asyncio" tests/

Test Database

Tests use a separate database with:

• Automatic creation/cleanup
• Transaction isolation
• Concurrent operation testing
• Row-level locking verification
• Connection pool stress testing

Performance Monitoring

Monitor system performance during load tests:

• Database connections: SELECT count(*) FROM pg_stat_activity;
• Connection pools: Check pool usage in application logs
• System resources: Use htop or similar tools
• Response times: Monitor through Locust UI
• Transaction duration: Check application logs

API Documentation

Available at http://localhost:8000/docs

Error Handling

• 400 - Bad Request (e.g., insufficient funds)
• 404 - Wallet not found
• 422 - Validation error (e.g., negative amount)

All other errors return 200 OK with operation status "FAILED" and details in the response body.

PgBouncer Monitoring

Monitor connection pooling:

-- Active pools
SHOW POOLS;
-- Connection stats
SHOW STATS;
-- Server status
SHOW SERVERS;
-- Current connections
SHOW CLIENTS;
-- Transaction status
SHOW TOTALS;

Connection Pooling

The service uses PgBouncer for connection pooling with:

• Transaction pooling mode
• Dynamic user authentication
• Connection limits and timeouts
• Monitoring capabilities
• Automatic connection cleanup

Development

• Use pytest.mark.asyncio for async tests
• Implement proper cleanup in test fixtures
• Use row-level locking for concurrent operations
• Monitor transaction duration
• Handle database connection errors gracefully