Backend Technical Design Document¶

Core Dependencies¶

Framework and API¶

FastAPI: Main web framework
Request handling and routing
Dependency injection
OpenAPI/Swagger integration
WebSocket support
Background tasks

Database and ORM¶

SQLModel + SQLAlchemy: Database ORM and modeling
Model definitions
Query building
Relationship management
Type safety integration
Alembic: Database migrations
Schema version control
Migration generation
Upgrade/downgrade operations
Multi-tenant schema management

File and Media Handling¶

python-multipart: File upload handling
Multipart form data processing
File streaming
Memory-efficient uploads
boto3: AWS S3 Integration
File storage operations
Bucket management
Access control
Pre-signed URLs

Email and Templates¶

emails: Email handling
SMTP integration
HTML email support
Email queue management
Jinja2: Template engine
Email template rendering
Dynamic content generation
Template inheritance
Custom filters and extensions

Security and Authentication¶

python-jose[cryptography]: JWT handling
Token generation and validation
Encryption/decryption
passlib[bcrypt]: Password hashing
Secure password storage
Hash verification
python-multipart: Form data parsing
Authentication request handling

Caching and Performance¶

Redis: Distributed caching
Session storage
Rate limiting
Cache invalidation

Testing and Quality¶

pytest: Testing framework
Unit testing
Integration testing
Fixtures and mocking
httpx: HTTP client
API testing
External service integration
coverage: Code coverage
Test coverage reporting
Coverage enforcement

Architecture Overview¶

graph TD
    A[API Layer] --> B[Service Layer]
    B --> C[Domain Layer]
    C --> D[Infrastructure Layer]
    D --> E[Database]
    D --> F[S3 Storage]

    subgraph Infrastructure
    D
    E
    F
    end

    subgraph Business Logic
    B
    C
    end

Core Architectural Principles¶

Domain-Driven Structure¶

Root directory organization by domain contexts
Each domain module is self-contained with its routes, services, models, and repositories
Cross-cutting concerns handled via middleware and shared utilities

app/
├── domains/
│   ├── auth/
│   ├── users/
│   ├── permissions/
│   ├── files/
│   └── tenant/
├── core/
├── infrastructure/
└── shared/

Layer Separation¶

API Layer
Route definitions and request/response handling
Input validation and serialization
Authentication and authorization middleware
API documentation via OpenAPI/Swagger
Service Layer
Business logic orchestration
Transaction management
Cross-domain coordination
Event handling and dispatching
Domain Layer
Business entities and value objects
Domain-specific business rules
Interface definitions for repositories
Infrastructure Layer
Database operations and migrations
External service integrations
Caching implementation
File storage operations

Multi-Tenant Architecture¶

graph LR
    A[Request] --> B[Tenant Middleware]
    B --> C[Schema Router]
    C --> D[Public Schema]
    C --> E[Tenant Schema 1]
    C --> F[Tenant Schema 2]

Schema Design¶

Public schema for shared tables
Tenant registry
Global configurations
Shared lookup tables
Tenant-specific schemas
Isolated data per tenant
Independent configurations
Tenant-specific business data

Tenant Resolution¶

Header-based tenant identification
Tenant context middleware
Dynamic schema switching
Connection pooling per tenant

Permission System¶

graph TD
    A[Endpoint Request] --> B[Permission Middleware]
    B --> C[Permission Registry]
    C --> D[Tenant Config]
    B --> E[Role Resolver]
    E --> F[Access Decision]

Components¶

Permission registry for endpoint-based access control
Role-based access control (RBAC) implementation
Tenant-specific permission configurations
Permission inheritance and hierarchy support
Caching layer for permission checks

Data Persistence¶

Database Design¶

SQLAlchemy for ORM and query building
SQLModel for Pydantic integration
Alembic for schema migrations
Transaction management and unit of work pattern
Query optimization and indexing strategies

Caching Strategy¶

Multi-level caching approach
Redis for distributed caching
Local memory caching for frequently accessed data
Cache invalidation patterns

File Storage Integration¶

S3 Integration¶

Abstracted storage interface
Tenant-specific bucket/prefix strategy
File metadata tracking
Access control and signed URLs
Bulk operation support

Error Handling & Logging¶

Error Management¶

Standardized error response format
Domain-specific error types
Error tracking and monitoring
Graceful degradation strategies

Logging System¶

Structured logging format
Log levels and categorization
Correlation IDs for request tracking
Performance monitoring integration

Security Implementation¶

Authentication¶

JWT-based authentication
Token refresh mechanism
Session management
MFA support structure

Authorization¶

Role-based access control
Permission verification middleware
Resource-level access control
Audit logging

Code Generation & CLI Tools¶

Template System¶

Code generation templates for:
Domain modules
CRUD operations
Service layers
Test structures

CLI Features¶

Module scaffolding
Migration management
Tenant operations
Permission management

Testing Strategy¶

Test Categories¶

Unit tests for domain logic
Integration tests for services
API tests for endpoints
Performance tests for critical paths

Testing Principles¶

Isolated test environments per tenant
Mock external dependencies
Fixture-based test data
Parallel test execution support

API Documentation¶

Documentation Approach¶

OpenAPI/Swagger integration
Automated documentation generation
Interactive API documentation
Code example generation

Performance Considerations¶

Optimization Strategies¶

Query optimization
Caching strategies
Lazy loading patterns
Bulk operation support
Connection pooling
Resource monitoring