# Software Architecture Document

**Project**: [Project Name]
**Version**: 1.0
**Date**: [YYYY-MM-DD]
**Architect**: Marcus-Backend
**Status**: Draft

---

## 1. Executive Summary

### 1.1 Architecture Overview
[High-level summary of the architecture, key design decisions, and the overall approach]

### 1.2 System Purpose
[Brief description of what the system does and why it exists]

### 1.3 Key Architectural Decisions
| Decision | Rationale | Impact |
|----------|-----------|--------|
| [Decision 1] | [Why this choice] | [Impact on system] |
| [Decision 2] | [Why this choice] | [Impact on system] |

---

## 2. Architectural Goals & Constraints

### 2.1 Business Goals
- **Goal 1**: [Business objective the architecture supports]
- **Goal 2**: [Business objective the architecture supports]
- **Goal 3**: [Business objective the architecture supports]

### 2.2 Technical Goals
- **Scalability**: [Target scale and requirements]
- **Performance**: [Performance requirements]
- **Reliability**: [Uptime and reliability targets]
- **Security**: [Security requirements and compliance]
- **Maintainability**: [Code quality and maintenance goals]

### 2.3 Quality Attributes (FURPS+)
| Attribute | Target | Measurement |
|-----------|--------|------------|
| **Functionality** | [Requirements] | [How measured] |
| **Usability** | [Requirements] | [How measured] |
| **Reliability** | [Requirements] | [How measured] |
| **Performance** | [Requirements] | [How measured] |
| **Supportability** | [Requirements] | [How measured] |

### 2.4 Constraints
- **Technical**: [Technology limitations]
- **Budget**: [Financial constraints]
- **Timeline**: [Schedule constraints]
- **Resources**: [Team/infrastructure constraints]
- **Regulatory**: [Compliance requirements]

---

## 3. System Context

### 3.1 System Boundary
[Diagram or description of what's inside vs. outside the system]

### 3.2 External Systems & Integrations
| System | Type | Purpose | Protocol | SLA |
|--------|------|---------|----------|-----|
| [System 1] | [Internal/External] | [Purpose] | [REST/GraphQL/gRPC] | [SLA] |
| [System 2] | [Internal/External] | [Purpose] | [REST/GraphQL/gRPC] | [SLA] |

### 3.3 Users & Actors
| Actor | Type | Interaction Method | Use Cases |
|-------|------|-------------------|-----------|
| [Actor 1] | [Human/System] | [Web/API/CLI] | [Primary use cases] |
| [Actor 2] | [Human/System] | [Web/API/CLI] | [Primary use cases] |

---

## 4. Architecture Style & Patterns

### 4.1 Primary Architecture Style
**Style**: [Microservices / Monolithic / Serverless / Event-Driven / etc.]

**Rationale**: [Why this style was chosen]

**Trade-offs**:
- **Pros**: [Advantages of this approach]
- **Cons**: [Disadvantages and how we mitigate them]

### 4.2 Design Patterns Used
| Pattern | Where Applied | Purpose |
|---------|--------------|---------|
| [Pattern 1] | [Component/Layer] | [Why used] |
| [Pattern 2] | [Component/Layer] | [Why used] |

### 4.3 Architectural Principles
1. **[Principle 1]**: [Description and how it guides design]
2. **[Principle 2]**: [Description and how it guides design]
3. **[Principle 3]**: [Description and how it guides design]

---

## 5. High-Level Architecture

### 5.1 System Architecture Diagram
```
┌─────────────────────────────────────────────────────┐
│                   Load Balancer                     │
└────────────────────┬────────────────────────────────┘
                     │
         ┌───────────┴───────────┐
         │                       │
    ┌────▼────┐            ┌────▼────┐
    │ API GW 1│            │ API GW 2│
    └────┬────┘            └────┬────┘
         │                       │
    ┌────▼───────────────────────▼────┐
    │        Service Layer             │
    │  ┌──────┐  ┌──────┐  ┌──────┐  │
    │  │Svc A │  │Svc B │  │Svc C │  │
    │  └──┬───┘  └──┬───┘  └──┬───┘  │
    └─────┼─────────┼─────────┼───────┘
          │         │         │
    ┌─────▼─────────▼─────────▼───────┐
    │         Data Layer               │
    │  ┌─────┐  ┌─────┐  ┌─────┐     │
    │  │ DB  │  │Cache│  │Queue│     │
    │  └─────┘  └─────┘  └─────┘     │
    └──────────────────────────────────┘
```

### 5.2 Component Overview
| Component | Responsibility | Technology | Scaling Strategy |
|-----------|---------------|------------|-----------------|
| [Component 1] | [What it does] | [Tech stack] | [Horizontal/Vertical] |
| [Component 2] | [What it does] | [Tech stack] | [Horizontal/Vertical] |

---

## 6. Detailed Component Design

### 6.1 Component: [Component Name]

#### Purpose
[What this component does and why it exists]

#### Responsibilities
- [Responsibility 1]
- [Responsibility 2]
- [Responsibility 3]

#### Technology Stack
- **Language**: [Programming language]
- **Framework**: [Framework used]
- **Libraries**: [Key libraries]
- **Runtime**: [Node.js, Python, etc.]

#### Interfaces
**Public API**:
```
GET /api/v1/resource
POST /api/v1/resource
PUT /api/v1/resource/:id
DELETE /api/v1/resource/:id
```

**Internal Communication**:
- [How it communicates with other components]

#### Data Model
```typescript
interface Resource {
  id: string;
  name: string;
  status: 'active' | 'inactive';
  createdAt: Date;
  updatedAt: Date;
}
```

#### Dependencies
- **Upstream**: [Services this depends on]
- **Downstream**: [Services that depend on this]

#### Performance Characteristics
- **Throughput**: [Requests/second]
- **Latency**: [p50, p95, p99]
- **Resource Usage**: [CPU, Memory]

---

## 7. Data Architecture

### 7.1 Data Storage Strategy
| Data Type | Storage Solution | Rationale | Retention |
|-----------|-----------------|-----------|-----------|
| [Transactional] | [PostgreSQL] | [Why chosen] | [Duration] |
| [Session] | [Redis] | [Why chosen] | [Duration] |
| [Analytics] | [BigQuery] | [Why chosen] | [Duration] |

### 7.2 Database Schema
**Primary Database**: [Database name and type]

**Key Tables**:
```sql
CREATE TABLE users (
  id UUID PRIMARY KEY,
  email VARCHAR(255) UNIQUE NOT NULL,
  name VARCHAR(255),
  created_at TIMESTAMP DEFAULT NOW(),
  updated_at TIMESTAMP DEFAULT NOW()
);

CREATE TABLE resources (
  id UUID PRIMARY KEY,
  user_id UUID REFERENCES users(id),
  name VARCHAR(255),
  status VARCHAR(50),
  created_at TIMESTAMP DEFAULT NOW()
);
```

### 7.3 Data Flow Diagram
```
User → API → Validation → Business Logic → Database
                              ↓
                         Cache Update
                              ↓
                        Event Publishing
```

### 7.4 Data Consistency Strategy
- **ACID Transactions**: [Where used]
- **Eventual Consistency**: [Where used]
- **Conflict Resolution**: [How handled]

### 7.5 Data Migration Strategy
- **Schema Changes**: [How managed]
- **Data Migrations**: [Tools and process]
- **Rollback Plan**: [How to rollback]

---

## 8. API Design

### 8.1 API Style
**Style**: [REST / GraphQL / gRPC / Hybrid]

**Versioning Strategy**: [URL versioning / Header versioning]

### 8.2 API Endpoints
| Endpoint | Method | Purpose | Auth Required | Rate Limit |
|----------|--------|---------|--------------|------------|
| `/api/v1/users` | GET | List users | Yes | 100/min |
| `/api/v1/users/:id` | GET | Get user | Yes | 1000/min |
| `/api/v1/users` | POST | Create user | Yes | 10/min |

### 8.3 Request/Response Format
**Request Example**:
```json
POST /api/v1/users
Content-Type: application/json

{
  "email": "user@example.com",
  "name": "John Doe",
  "role": "admin"
}
```

**Response Example**:
```json
HTTP/1.1 201 Created
Content-Type: application/json

{
  "id": "uuid-here",
  "email": "user@example.com",
  "name": "John Doe",
  "role": "admin",
  "createdAt": "2025-01-15T10:00:00Z"
}
```

### 8.4 Error Handling
**Error Format**:
```json
{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Email is required",
    "details": {
      "field": "email",
      "constraint": "required"
    }
  }
}
```

**Error Codes**:
| Code | HTTP Status | Description |
|------|-------------|-------------|
| `VALIDATION_ERROR` | 400 | Invalid request data |
| `UNAUTHORIZED` | 401 | Missing or invalid auth |
| `FORBIDDEN` | 403 | Insufficient permissions |
| `NOT_FOUND` | 404 | Resource not found |
| `RATE_LIMIT_EXCEEDED` | 429 | Too many requests |
| `INTERNAL_ERROR` | 500 | Server error |

---

## 9. Security Architecture

### 9.1 Security Principles
- **Defense in Depth**: [Multiple layers of security]
- **Least Privilege**: [Minimal access rights]
- **Zero Trust**: [Verify everything]
- **Secure by Default**: [Secure configurations]

### 9.2 Authentication & Authorization
**Authentication**:
- **Method**: [JWT / OAuth 2.0 / SAML]
- **Token Storage**: [Where tokens are stored]
- **Token Expiry**: [Lifetime and refresh strategy]

**Authorization**:
- **Model**: [RBAC / ABAC / ACL]
- **Permissions**: [How permissions are managed]
- **Enforcement**: [Where authorization is checked]

### 9.3 OWASP Top 10 Mitigation
| Vulnerability | Mitigation Strategy |
|--------------|-------------------|
| A01: Broken Access Control | [How mitigated] |
| A02: Cryptographic Failures | [How mitigated] |
| A03: Injection | [How mitigated] |
| A04: Insecure Design | [How mitigated] |
| A05: Security Misconfiguration | [How mitigated] |
| A06: Vulnerable Components | [How mitigated] |
| A07: Auth & Session Management | [How mitigated] |
| A08: Software & Data Integrity | [How mitigated] |
| A09: Logging & Monitoring | [How mitigated] |
| A10: SSRF | [How mitigated] |

### 9.4 Data Security
- **Encryption at Rest**: [How data is encrypted]
- **Encryption in Transit**: [TLS version, ciphers]
- **Key Management**: [How keys are managed]
- **PII Handling**: [How PII is protected]

### 9.5 Security Monitoring
- **Intrusion Detection**: [Tools and approach]
- **Vulnerability Scanning**: [Frequency and tools]
- **Penetration Testing**: [Schedule and scope]
- **Security Audits**: [Frequency and process]

---

## 10. Performance & Scalability

### 10.1 Performance Requirements
| Metric | Target | Current | Monitoring |
|--------|--------|---------|------------|
| API Response Time (p95) | < 200ms | [Current] | [Tool] |
| Database Query Time (p95) | < 50ms | [Current] | [Tool] |
| Page Load Time | < 2s | [Current] | [Tool] |
| Throughput | 1000 req/s | [Current] | [Tool] |

### 10.2 Caching Strategy
| Layer | Technology | TTL | Invalidation Strategy |
|-------|-----------|-----|---------------------|
| CDN | CloudFlare | 1 hour | Path-based purge |
| Application | Redis | 15 min | Event-based invalidation |
| Database | Query cache | 5 min | Automatic |

### 10.3 Scaling Strategy
**Horizontal Scaling**:
- **Stateless Services**: [Auto-scaling rules]
- **Database**: [Read replicas, sharding]
- **Cache**: [Redis cluster]

**Vertical Scaling**:
- **When Used**: [Scenarios where vertical scaling is appropriate]
- **Limits**: [Maximum scale before horizontal scaling]

### 10.4 Load Balancing
- **Strategy**: [Round-robin / Least connections / IP hash]
- **Health Checks**: [How health is determined]
- **Failover**: [How failures are handled]

---

## 11. Reliability & Resilience

### 11.1 Reliability Targets
- **Availability**: 99.9% (8.76 hours downtime/year)
- **RPO (Recovery Point Objective)**: [Data loss tolerance]
- **RTO (Recovery Time Objective)**: [Recovery time target]

### 11.2 Failure Modes & Mitigations
| Failure Scenario | Impact | Mitigation | Detection |
|-----------------|--------|------------|-----------|
| [Service failure] | [Impact] | [How handled] | [How detected] |
| [Database failure] | [Impact] | [How handled] | [How detected] |
| [Network partition] | [Impact] | [How handled] | [How detected] |

### 11.3 Resilience Patterns
- **Circuit Breaker**: [Where applied and configuration]
- **Retry Logic**: [Retry strategy and backoff]
- **Bulkheads**: [Resource isolation strategy]
- **Timeout**: [Timeout configurations]

### 11.4 Disaster Recovery
**Backup Strategy**:
- **Frequency**: [Backup schedule]
- **Retention**: [How long backups are kept]
- **Testing**: [DR testing schedule]

**Recovery Procedures**:
1. [Step 1: Detection and assessment]
2. [Step 2: Failover initiation]
3. [Step 3: Recovery verification]
4. [Step 4: Post-mortem]

---

## 12. Monitoring & Observability

### 12.1 Monitoring Stack
| Component | Tool | Purpose |
|-----------|------|---------|
| Metrics | Prometheus | System metrics |
| Logging | ELK Stack | Centralized logging |
| Tracing | Jaeger | Distributed tracing |
| APM | Datadog | Application performance |
| Alerting | PagerDuty | Incident management |

### 12.2 Key Metrics
**Golden Signals**:
- **Latency**: [Target and current]
- **Traffic**: [Target and current]
- **Errors**: [Target error rate]
- **Saturation**: [Resource utilization targets]

**Business Metrics**:
- [Custom business metric 1]
- [Custom business metric 2]

### 12.3 Logging Strategy
**Log Levels**:
- **ERROR**: Critical issues requiring immediate attention
- **WARN**: Potential issues to monitor
- **INFO**: Important business events
- **DEBUG**: Detailed troubleshooting information

**Log Format**:
```json
{
  "timestamp": "2025-01-15T10:00:00Z",
  "level": "INFO",
  "service": "api-gateway",
  "traceId": "uuid",
  "message": "Request processed",
  "metadata": {
    "userId": "uuid",
    "endpoint": "/api/v1/users",
    "duration": 150
  }
}
```

### 12.4 Alerting Strategy
| Alert | Condition | Severity | Action |
|-------|-----------|----------|--------|
| [Alert 1] | [Threshold] | Critical | [Response] |
| [Alert 2] | [Threshold] | Warning | [Response] |

---

## 13. Deployment Architecture

### 13.1 Infrastructure Overview
**Cloud Provider**: [AWS / GCP / Azure]

**Regions**: [Primary and backup regions]

**Environment Strategy**:
- **Development**: [Configuration]
- **Staging**: [Configuration]
- **Production**: [Configuration]

### 13.2 Deployment Pipeline
```
Code Push → CI (Tests) → Build → Staging Deploy → E2E Tests → Production Deploy → Health Check
```

**CI/CD Tools**:
- **CI**: [GitHub Actions / Jenkins / CircleCI]
- **CD**: [ArgoCD / Spinnaker / GitLab CD]
- **Infrastructure**: [Terraform / CloudFormation]

### 13.3 Container Strategy
**Containerization**: [Docker / containerd]

**Orchestration**: [Kubernetes / ECS / Cloud Run]

**Example Kubernetes Deployment**:
```yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-service
spec:
  replicas: 3
  selector:
    matchLabels:
      app: api-service
  template:
    metadata:
      labels:
        app: api-service
    spec:
      containers:
      - name: api
        image: api-service:latest
        ports:
        - containerPort: 8080
        resources:
          limits:
            cpu: "1"
            memory: "512Mi"
          requests:
            cpu: "500m"
            memory: "256Mi"
```

### 13.4 Blue-Green / Canary Deployment
- **Strategy**: [Blue-green / Canary / Rolling]
- **Traffic Splitting**: [How traffic is routed]
- **Rollback**: [Automated rollback conditions]

---

## 14. Development Guidelines

### 14.1 Code Organization
```
project/
├── src/
│   ├── api/          # API layer
│   ├── services/     # Business logic
│   ├── models/       # Data models
│   ├── utils/        # Utilities
│   └── config/       # Configuration
├── tests/
│   ├── unit/
│   ├── integration/
│   └── e2e/
├── docs/
└── infra/            # Infrastructure as code
```

### 14.2 Coding Standards
- **Language**: [Primary language and version]
- **Style Guide**: [Style guide followed]
- **Linting**: [ESLint / Pylint / etc.]
- **Formatting**: [Prettier / Black / etc.]

### 14.3 Testing Strategy
| Test Type | Coverage Target | Tools | Frequency |
|-----------|----------------|-------|-----------|
| Unit | 80%+ | Jest | Every commit |
| Integration | Critical paths | Jest | Pre-deploy |
| E2E | User journeys | Playwright | Pre-deploy |
| Load | Baseline | k6 | Weekly |
| Security | OWASP Top 10 | Semgrep | Daily |

---

## 15. Migration & Evolution

### 15.1 Current State
[Description of existing system if this is a migration/evolution]

### 15.2 Migration Strategy
**Approach**: [Big bang / Strangler fig / Parallel run]

**Phases**:
1. **Phase 1**: [Description and timeline]
2. **Phase 2**: [Description and timeline]
3. **Phase 3**: [Description and timeline]

### 15.3 Deprecation Plan
[How old systems/APIs will be deprecated]

---

## 16. Trade-offs & Technical Debt

### 16.1 Known Trade-offs
| Decision | Trade-off | Rationale | Future Action |
|----------|-----------|-----------|--------------|
| [Decision 1] | [What we gave up] | [Why it was worth it] | [When to revisit] |

### 16.2 Technical Debt Register
| Debt Item | Impact | Priority | Plan to Address |
|-----------|--------|----------|----------------|
| [Item 1] | [Impact] | [Priority] | [Remediation plan] |

---

## 17. Appendix

### 17.1 Glossary
- **Term 1**: [Definition]
- **Term 2**: [Definition]

### 17.2 References
- **Related Documents**: [Links]
- **External Resources**: [Links]
- **Standards**: [Relevant standards]

### 17.3 Change Log
| Version | Date | Author | Changes |
|---------|------|--------|---------|
| 1.0 | [YYYY-MM-DD] | Marcus-Backend | Initial architecture document |

---

**Architecture Document Generated by**: Marcus-Backend (VERSATIL SDLC Framework)
**Template Version**: 1.0
**Framework Version**: 6.1.0
**Review Status**: [Pending/Approved]
**Next Review**: [YYYY-MM-DD]
