# Design Document Template

## Document Information
- **Document ID**: DESIGN-[PROJECT]-[VERSION]
- **Project**: [Project Name]
- **Version**: [X.Y.Z]
- **Date**: [YYYY-MM-DD]
- **Author**: [Name]
- **Reviewers**: [Names]
- **Status**: [Draft/Review/Approved/Implemented]

## 1. Overview
### 1.1 Purpose
Brief description of the system being designed.

### 1.2 Scope
What this design document covers.

### 1.3 Related Documents
- Requirements Document: [Link]
- Architecture Decision Records: [Link]
- API Specifications: [Link]

## 2. System Architecture
### 2.1 High-Level Architecture
```
[Include architecture diagram]
```

### 2.2 Component Overview
| Component | Responsibility | Technology | Dependencies |
|-----------|---------------|------------|--------------|
| | | | |

### 2.3 Data Flow
Description of how data flows through the system.

## 3. Detailed Design
### 3.1 Core Components
#### Component Name
- **Purpose**: What this component does
- **Interface**: Public methods/APIs
- **Implementation**: Key implementation details
- **Dependencies**: What this component depends on

### 3.2 Database Design
#### Entity Relationship Diagram
```
[Include ERD]
```

#### Table Specifications
| Table | Purpose | Key Fields | Relationships |
|-------|---------|------------|---------------|
| | | | |

### 3.3 API Design
#### REST Endpoints
| Method | Endpoint | Purpose | Request | Response |
|--------|----------|---------|---------|----------|
| GET | /api/v1/resource | | | |
| POST | /api/v1/resource | | | |

#### GraphQL Schema (if applicable)
```graphql
type Resource {
  id: ID!
  name: String!
}
```

## 4. Security Design
### 4.1 Authentication
- Authentication mechanism
- Token management
- Session handling

### 4.2 Authorization
- Role-based access control
- Permission model
- Resource protection

### 4.3 Data Protection
- Encryption at rest
- Encryption in transit
- PII handling

## 5. Performance Design
### 5.1 Performance Requirements
- Response time targets
- Throughput targets
- Concurrent user targets

### 5.2 Caching Strategy
- Cache layers
- Cache invalidation
- Cache warming

### 5.3 Optimization Strategies
- Database optimization
- Code optimization
- Infrastructure optimization

## 6. Error Handling
### 6.1 Error Categories
- System errors
- Business logic errors
- Validation errors

### 6.2 Error Response Format
```json
{
  "error": {
    "code": "ERROR_CODE",
    "message": "Human readable message",
    "details": {}
  }
}
```

## 7. Monitoring and Observability
### 7.1 Metrics
- Key performance indicators
- Business metrics
- Technical metrics

### 7.2 Logging
- Log levels
- Log format
- Log retention

### 7.3 Alerting
- Alert conditions
- Escalation procedures
- Response procedures

## 8. Deployment Design
### 8.1 Environment Strategy
- Development environment
- Staging environment
- Production environment

### 8.2 Deployment Pipeline
- Build process
- Testing stages
- Deployment stages

### 8.3 Rollback Strategy
- Rollback triggers
- Rollback procedure
- Data migration rollback

## 9. Testing Strategy
### 9.1 Unit Testing
- Test coverage targets
- Mock strategies
- Test data management

### 9.2 Integration Testing
- API testing
- Database testing
- External service testing

### 9.3 Performance Testing
- Load testing
- Stress testing
- Endurance testing

## 10. Migration Plan (if applicable)
### 10.1 Data Migration
- Migration strategy
- Data validation
- Rollback plan

### 10.2 Feature Migration
- Feature flag strategy
- Gradual rollout
- User communication

## 11. Open Questions
- [ ] Question 1
- [ ] Question 2
- [ ] Question 3

## 12. Approval
| Role | Name | Signature | Date |
|------|------|-----------|------|
| Architect | | | |
| Tech Lead | | | |
| Security Review | | | |

## 13. Revision History
| Version | Date | Author | Changes |
|---------|------|--------|---------|
| 1.0 | | | Initial draft |