# Architecture Documentation

## Overview

The Enterprise Service is a production-ready REST API microservice built with Rust, demonstrating Gold-level Rhodium compliance. It follows modern architectural patterns and best practices for cloud-native applications.

## System Architecture

### High-Level Architecture

```
┌─────────────────────────────────────────────────────┐
│                   Load Balancer                      │
└──────────────────┬──────────────────────────────────┘
                   │
    ┌──────────────┼──────────────┐
    │              │              │
    ▼              ▼              ▼
┌────────┐    ┌────────┐    ┌────────┐
│Service │    │Service │    │Service │
│Instance│    │Instance│    │Instance│
└────────┘    └────────┘    └────────┘
    │              │              │
    └──────────────┼──────────────┘
                   │
                   ▼
          ┌────────────────┐
          │   Data Store   │
          │ (Future: DB)   │
          └────────────────┘
```

### Component Architecture

```
┌─────────────────────────────────────┐
│         HTTP Layer (Axum)           │
│  - Routing                          │
│  - Middleware (Compression, Trace)  │
│  - Request/Response handling        │
└───────────────┬─────────────────────┘
                │
                ▼
┌─────────────────────────────────────┐
│         Handler Layer               │
│  - Business logic                   │
│  - Input validation                 │
│  - Error handling                   │
└───────────────┬─────────────────────┘
                │
                ▼
┌─────────────────────────────────────┐
│         State Management            │
│  - Shared application state         │
│  - Concurrent access control        │
│  - Data storage (in-memory)         │
└─────────────────────────────────────┘
```

## Technology Stack

### Core Technologies

- **Language**: Rust 1.70+
- **Web Framework**: Axum 0.7
- **Async Runtime**: Tokio 1.35
- **Serialization**: Serde 1.0

### Supporting Libraries

- **Logging**: tracing + tracing-subscriber
- **Error Handling**: thiserror
- **HTTP Middleware**: tower-http
- **Configuration**: config

### Development Tools

- **Testing**: cargo test, tokio-test, axum-test
- **Benchmarking**: criterion
- **Code Quality**: clippy, rustfmt
- **Documentation**: rustdoc

## Module Structure

```
enterprise-service/
├── src/
│   ├── main.rs           # Application entry point & server setup
│   ├── lib.rs            # Library exports for testing/benchmarking
│   ├── handlers.rs       # Request handlers (business logic)
│   ├── models.rs         # Data models & DTOs
│   ├── state.rs          # Application state management
│   └── error.rs          # Error types & handling
├── benches/
│   └── api_benchmarks.rs # Performance benchmarks
└── tests/               # Integration tests
```

## API Design

### RESTful Endpoints

| Method | Endpoint              | Description           |
|--------|----------------------|-----------------------|
| GET    | /health              | Health check          |
| GET    | /build-info          | Build metadata        |
| GET    | /api/v1/users        | List all users        |
| POST   | /api/v1/users        | Create a new user     |
| GET    | /api/v1/users/:id    | Get user by ID        |
| DELETE | /api/v1/users/:id    | Delete user by ID     |

### Request/Response Flow

1. **Request arrives** at the Axum router
2. **Middleware** processes request (compression, tracing)
3. **Handler** extracts parameters and validates input
4. **State** is accessed (with appropriate locking)
5. **Business logic** executes
6. **Response** is formatted and returned
7. **Middleware** processes response (compression)

## Data Models

### User

```rust
pub struct User {
    pub id: String,
    pub name: String,
    pub email: String,
}
```

### Error Handling

All errors are typed and handled consistently:

- `UserNotFound` → HTTP 404
- `InvalidInput` → HTTP 400
- `Internal` → HTTP 500

## Concurrency Model

### Thread Safety

- **Read-Write Locks**: RwLock for user storage allows concurrent reads
- **Atomic Operations**: Future database operations will use connection pooling
- **Async/Await**: All I/O operations are non-blocking

### Performance Characteristics

- **Concurrent Reads**: Multiple threads can read user data simultaneously
- **Write Operations**: Serialized to prevent data races
- **Request Handling**: Each request is handled on a separate Tokio task

## Security Considerations

See [SECURITY.md](SECURITY.md) for detailed security documentation.

### Key Security Features

1. **Input Validation**: All user inputs are validated
2. **Error Handling**: No sensitive information leaked in errors
3. **HTTPS Ready**: Production deployment requires TLS
4. **Dependency Scanning**: Regular security audits via cargo-audit

## Scalability

### Horizontal Scaling

- Stateless design allows multiple instances
- Load balancer distributes requests
- Future: External database for shared state

### Vertical Scaling

- Efficient memory usage with Rust's zero-cost abstractions
- Low CPU overhead with async I/O
- Tunable worker threads via Tokio configuration

## Deployment

### Container Deployment

```dockerfile
# Multi-stage build for minimal image size
FROM rust:1.70 as builder
WORKDIR /app
COPY . .
RUN cargo build --release

FROM debian:bookworm-slim
COPY --from=builder /app/target/release/enterprise-service /usr/local/bin/
CMD ["enterprise-service"]
```

### Configuration

Environment variables:
- `RUST_LOG`: Logging level
- `SERVER_PORT`: Server port (default: 3000)
- `DATABASE_URL`: Future database connection string

## Monitoring & Observability

### Logging

- Structured logging via tracing
- Configurable log levels
- Request/response correlation

### Metrics

- Health check endpoint for liveness probes
- Build info endpoint for version tracking
- Future: Prometheus metrics

### Tracing

- Distributed tracing support via tracing
- HTTP request/response tracing
- Performance profiling hooks

## Performance

### Benchmarks

Criterion benchmarks track:
- User listing performance
- User creation latency
- Concurrent request handling

See `cargo bench` for results.

### Optimization

- Release builds use LTO and optimization level 3
- Zero-copy deserialization where possible
- Efficient memory management with Rust's ownership system

## Future Enhancements

See [docs/adr/](docs/adr/) for architecture decisions.

### Planned Features

1. **Database Integration**: PostgreSQL with connection pooling
2. **Authentication**: JWT-based auth system
3. **API Versioning**: Proper API version management
4. **Caching**: Redis integration for performance
5. **Message Queue**: Event-driven architecture
6. **GraphQL**: Alternative API interface

## Testing Strategy

### Unit Tests

- Handler logic tested in isolation
- Model validation tested
- Error handling verified

### Integration Tests

- Full HTTP request/response cycle
- State management under concurrent access
- Error scenarios end-to-end

### Benchmarks

- Performance regression detection
- Latency tracking
- Throughput measurement

## Dependencies Management

### SBOM Generation

Software Bill of Materials tracked via:
- Cargo.lock for reproducible builds
- cargo-sbom for SBOM generation
- Regular dependency audits

### Update Strategy

- Automated dependency updates via Dependabot
- Security patches applied immediately
- Major version updates reviewed carefully

## References

- [Rust API Guidelines](https://rust-lang.github.io/api-guidelines/)
- [Axum Documentation](https://docs.rs/axum/)
- [Tokio Best Practices](https://tokio.rs/tokio/tutorial)

---

**Last Updated**: 2025-11-22
**Version**: 1.0.0
