---
title: "System Design"
description: "High-level system architecture and design of TraceRTM"
keywords: [architecture, system design, design, structure]
---

# System Design

High-level architecture and design principles of TraceRTM.

## Architecture Overview

### Layered Architecture

```
┌─────────────────────────────────────┐
│      Client Layer                  │
│  (CLI, TUI, Web UI, Desktop)      │
└──────────────┬──────────────────────┘
               │
┌──────────────▼──────────────────────┐
│      API Layer (FastAPI)           │
│  (REST Endpoints, Validation)       │
└──────────────┬──────────────────────┘
               │
┌──────────────▼──────────────────────┐
│      Service Layer                 │
│  (Business Logic, Orchestration)   │
└──────────────┬──────────────────────┘
               │
┌──────────────▼──────────────────────┐
│      Repository Layer              │
│  (Data Access, Abstraction)        │
└──────────────┬──────────────────────┘
               │
┌──────────────▼──────────────────────┐
│      Database Layer                │
│  (PostgreSQL, Redis)               │
└─────────────────────────────────────┘
```

## Core Principles

### 1. Separation of Concerns

- **API Layer**: HTTP handling, validation
- **Service Layer**: Business logic
- **Repository Layer**: Data access
- **Database Layer**: Data persistence

### 2. Dependency Injection

```python
# Services depend on abstractions, not implementations
class ItemService:
    def __init__(self, repo: ItemRepository, event_bus: EventBus):
        self.repo = repo
        self.event_bus = event_bus
```

### 3. Event-Driven Architecture

```python
# Loose coupling through events
item_service.create(data)
  → publishes "item.created" event
  → notification service handles event
  → search service indexes item
```

## Technology Stack

### Backend

- **FastAPI**: Web framework
- **SQLAlchemy**: ORM
- **PostgreSQL**: Primary database
- **Redis**: Caching (optional)
- **Alembic**: Migrations

### Frontend

- **Next.js**: React framework
- **TypeScript**: Type safety
- **Tailwind CSS**: Styling
- **Fumadocs**: Documentation

### CLI/TUI

- **Python**: Runtime
- **Click**: CLI framework
- **Textual**: TUI framework

## Design Patterns

### Repository Pattern

```python
# Abstract data access
class ItemRepository:
    async def get_by_id(self, id: str) -> Item:
        pass
    
    async def create(self, data: dict) -> Item:
        pass
```

### Service Pattern

```python
# Encapsulate business logic
class ItemService:
    def __init__(self, repo: ItemRepository):
        self.repo = repo
    
    async def create(self, data: dict) -> Item:
        # Business logic
        validate(data)
        # Data access
        return await self.repo.create(data)
```

### Event Bus Pattern

```python
# Decoupled communication
event_bus.publish("item.created", data)
  → handlers process event asynchronously
```

## Scalability

### Horizontal Scaling

- Stateless API servers
- Database read replicas
- Redis for shared cache
- Load balancer

### Vertical Scaling

- Increase instance size
- Optimize database queries
- Add caching layers

## Security

### Authentication

- JWT tokens
- API keys
- OAuth 2.0

### Authorization

- Role-based access control
- Scope-based permissions
- Resource-level permissions

## Related Documentation

- [Components](./03-components) - System components
- [Request Flow](./02a-request-flow) - Request processing
- [Data Flow](./02-data-flow) - Data flow patterns
