Architecture Decisions

# ADR-[NUMBER]: [TITLE]

## Status

[Proposed | Accepted | Deprecated | Superseded by ADR-XXX]

## Context

[Describe the situation, the problem, and the forces at play.
What is the issue that we're seeing that is motivating this decision?]

## Decision

[Describe the decision and the approach we're taking.
State the decision clearly and concisely.]

## Consequences

### Positive
- [List positive outcomes]

### Negative
- [List negative outcomes and trade-offs]

### Risks
- [List risks that this decision introduces]

## Alternatives Considered

### Alternative 1: [Name]
- Description: [Brief description]
- Pros: [Advantages]
- Cons: [Disadvantages]
- Reason not chosen: [Why this wasn't selected]

### Alternative 2: [Name]
[Same structure as above]

## Related Decisions

- [Links to related ADRs]

## References

- [Links to relevant documentation, articles, or resources]

## Notes

[Any additional context, meeting notes, or discussion points]

---

**Date:** [YYYY-MM-DD]
**Author:** [Name]
**Reviewers:** [Names]

# ADR-001: Use React for Frontend Framework

## Status
Accepted

## Context
We need to select a frontend framework for our patient portal application.
The application requires:
- Complex interactive UI components
- Real-time updates
- Accessibility compliance (508)
- Strong TypeScript support
- Large ecosystem for healthcare-related components

Our team has experience with both Angular and React.

## Decision
We will use React with TypeScript for the frontend application.

## Consequences

### Positive
- Large talent pool for hiring
- Extensive component libraries available
- Strong TypeScript integration
- Flexible architecture decisions
- Active community and long-term support

### Negative
- Need to make additional architecture decisions (state management, routing)
- JSX learning curve for developers new to React
- More boilerplate compared to newer frameworks

### Risks
- React ecosystem fragmentation (many ways to do things)
- Potential for inconsistent patterns across teams

## Alternatives Considered

### Alternative 1: Angular
- Pros: Full framework with opinions, TypeScript-first
- Cons: Steeper learning curve, smaller talent pool
- Reason not chosen: Team has more React experience

### Alternative 2: Vue.js
- Pros: Gentle learning curve, good documentation
- Cons: Smaller ecosystem, fewer healthcare libraries
- Reason not chosen: Smaller talent pool in our market

## Related Decisions
- ADR-002: State Management with Redux Toolkit
- ADR-003: Component Library Selection

## References
- React documentation: https://react.dev
- Healthcare UI components: [internal wiki link]

---
Date: 2024-01-15
Author: Jane Smith
Reviewers: John Doe, Alice Johnson

# ADR-002: Immutable Audit Log Storage

## Status
Accepted

## Context
Our HIPAA-compliant application requires comprehensive audit logging with:
- Immutability (logs cannot be modified or deleted)
- High write throughput
- Long-term retention (7 years)
- Query capability for compliance reporting
- Cost-effective storage

## Decision
We will use a tiered approach:
1. Amazon Kinesis for real-time ingestion
2. S3 with Object Lock for immutable storage
3. Athena for ad-hoc queries
4. OpenSearch for operational queries (90-day window)

## Consequences

### Positive
- True immutability with S3 Object Lock
- Cost-effective long-term storage
- Scalable write throughput
- Flexible query options

### Negative
- More complex architecture
- Multiple services to maintain
- Query latency for historical data

### Risks
- AWS vendor lock-in
- Need expertise in multiple services
- Cost management for high-volume logs

## Alternatives Considered

### Alternative 1: Single database (PostgreSQL)
- Pros: Simple, familiar
- Cons: No true immutability, expensive at scale
- Reason not chosen: Cannot guarantee immutability

### Alternative 2: Blockchain-based logging
- Pros: True immutability, tamper-evident
- Cons: Complex, expensive, overkill for use case
- Reason not chosen: Unnecessary complexity

---
Date: 2024-01-20
Author: Bob Wilson
Reviewers: Security Team, DBA Team

docs/
└── architecture/
    └── decisions/
        ├── 0001-use-postgresql-for-primary-database.md
        ├── 0002-implement-event-sourcing.md
        ├── 0003-select-react-for-frontend.md
        └── README.md (index of all ADRs)

# Architecture Decision Records

| ADR | Title | Status | Date |
|-----|-------|--------|------|
| [ADR-001](0001-use-postgresql.md) | Use PostgreSQL | Accepted | 2024-01-10 |
| [ADR-002](0002-event-sourcing.md) | Implement Event Sourcing | Accepted | 2024-01-15 |
| [ADR-003](0003-react-frontend.md) | Select React for Frontend | Accepted | 2024-01-20 |

# Initialize ADR directory
adr init docs/architecture/decisions

# Create new ADR
adr new "Use PostgreSQL for primary database"

# Supersede an ADR
adr new -s 2 "Use TimescaleDB for time-series data"

# Generate table of contents
adr generate toc > docs/architecture/decisions/README.md