# SDD + GitOps Documentation Framework

This document defines the documentation framework for the NATSBridge project. It establishes a structured approach to creating, maintaining, and evolving technical documentation in alignment with GitOps principles—ensuring that documentation is versioned, auditable, and continuously validated alongside the codebase.

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## The SDD Framework: Seven Pillars of Documentation

| Document | Purpose (Rationale) | Primary Audience | Format / Content | Example (SaaS Context) | Measurement (KPI) |
|----------|---------------------|-----------------|------------------|------------------------|-------------------|
| **Requirements** | Capture the **business intent** — why we're building this and what success looks like. Defines boundaries and user-visible outcomes. | Stakeholders, Product Owners, Lead Developers | User stories, PRDs, acceptance criteria, non-functional constraints. | "System must process tabular data from Julia to SvelteKit UI with <200ms latency for 5-member teams." | 95% of requests complete <200ms (synthetic monitoring). |
| **Specification** | The **technical contract** — precise rules for inputs, outputs, and data shape. Ensures consistency across dev and test. | Developers, QA Engineers, CI/CD pipelines | OpenAPI, Protobuf, AsyncAPI. Endpoint definitions, schemas, error codes. | `contract.yaml` defining a NATS subject that accepts Arrow streams with snake_case headers. | 100% of messages validated against spec (CI block rate). |
| **Architecture** | The **blueprint** — how components fit together, interact, and scale. Guides system structure and trade-offs. | Architects, Senior Developers, DevOps | C4 diagrams, Mermaid.js, component/network/storage models. | Diagram showing 6-node cluster routing traffic via Caddy → Node.js API → Julia pods. | 100% of major decisions logged with trade-off analysis. |
| **Walkthrough** | The **story of flow** — shows how pieces connect end-to-end and why steps are sequenced. Builds intuition for new devs. | New Developers, Team Members | TOUR.md, Loom videos, sequence diagrams. Step-by-step traces with rationale. | "UI sends JSON → Node.js wraps Claim-Check → Julia pulls Arrow data (prevents NATS overflow)." | New developers ship feature in <2 days (PR timeline). |
| **Implementation** | The **real code** — business logic, helpers, tests, configs. Where design becomes executable. | Developers, Code Reviewers | Source code, README.md, unit tests, setup scripts. | Julia function for matrix calculation + SvelteKit component rendering table. | >80% unit test coverage, <5% drift from spec. |
| **Validation** | The **enforcer** — ensures implementation matches the spec. Blocks drift and human error. | Automation servers, QA, Lead Developers | CI jobs, contract tests, linting, integration checks. | CI job rejects PR with camelCase field not allowed by YAML spec. | <1% of PRs bypass validation gates. |
| **Runbook** | The **operational manual** — how the system lives in production, scales, and recovers. Guides on-call engineers. | DevOps, SREs, On-call Developers | K8s manifests, Helm charts, Markdown guides. Deployment, scaling, backup/restore, troubleshooting. | GitOps manifest ensuring 6 Julia replicas restart if memory >80%. | MTTR <15 minutes for P1 incidents. |

---

## Detailed Document Descriptions

### 1. Requirements

**Purpose**: Capture the *business intent* — why we're building this and what success looks like. Defines boundaries and user-visible outcomes.

**Why It Matters**:
- Aligns engineering efforts with business goals
- Provides a north star for feature development
- Establishes acceptance criteria before implementation begins
- Creates a contract between product and engineering

**Content Guidelines**:
- User stories with clear acceptance criteria (As a X, I want Y so that Z)
- Product Requirements Documents (PRDs) with success metrics
- Non-functional requirements (performance, security, scalability)
- Boundary definitions (what's in scope vs. out of scope)

**Best Practices**:
- Link each requirement to a measurable KPI
- Keep requirements testable and verifiable
- Maintain backward compatibility with existing requirements
- Review and update requirements as business context changes

---

### 2. Specification

**Purpose**: The *technical contract* — precise rules for inputs, outputs, and data shape. Ensures consistency across dev and test.

**Why It Matters**:
- Prevents implementation drift between components
- Enables contract testing in CI/CD pipelines
- Provides a single source of truth for data structures
- Facilitates integration between teams

**Content Guidelines**:
- API endpoint definitions (methods, paths, parameters)
- Request/response schemas (JSON, XML, Protobuf, AsyncAPI)
- Error codes and their meanings
- Data validation rules and constraints
- Rate limiting and quota definitions

**Best Practices**:
- Use formal specification languages (OpenAPI 3.0+, AsyncAPI)
- Version specifications alongside code
- Generate client SDKs from specifications
- Block CI on specification violations
- Document edge cases and error scenarios

---

### 3. Architecture

**Purpose**: The *blueprint* — how components fit together, interact, and scale. Guides system structure and trade-offs.

**Why It Matters**:
- Provides a mental model for system design
- Guides technical decision-making and trade-off analysis
- Facilitates onboarding of new architects and senior developers
- Documents scaling and performance considerations

**Content Guidelines**:
- C4 diagrams (Context, Container, Component levels)
- Mermaid.js flowcharts for sequence diagrams
- Component interaction diagrams
- Network topology and data flow
- Storage and caching strategies
- Scaling and resilience patterns

**Best Practices**:
- Use diagrams that are easy to update (Mermaid.js over static images)
- Document trade-off decisions with Rationale Documents
- Include scaling considerations for each component
- Document failure modes and recovery strategies
- Keep architecture diagrams versioned with code

---

### 4. Walkthrough

**Purpose**: The *story of flow* — shows how pieces connect end-to-end and why steps are sequenced. Builds intuition for new devs.

**Why It Matters**:
- Reduces onboarding time for new developers
- Provides context that code comments alone cannot convey
- Explains the "why" behind architectural decisions
- Helps identify gaps in the system design

**Content Guidelines**:
- Step-by-step flow descriptions with rationale
- Sequence diagrams showing request/response patterns
- "Tour of the codebase" guides
- Video walkthroughs (Loom, internal recordings)
- Debugging and tracing examples

**Best Practices**:
- Walk through real user journeys, not just technical flows
- Include "what could go wrong" scenarios
- Link walkthroughs to relevant code locations
- Keep walkthroughs updated with architecture changes
- Make walkthroughs interactive where possible

---

### 5. Implementation

**Purpose**: The *real code* — business logic, helpers, tests, configs. Where design becomes executable.

**Why It Matters**:
- This is the actual artifact that runs in production
- Code is the ultimate source of truth (when it matches spec)
- Tests validate correctness and prevent regressions
- Configuration files define runtime behavior

**Content Guidelines**:
- Business logic implementation
- Helper functions and utilities
- Unit and integration tests
- Configuration files (YAML, JSON, environment)
- Setup and development scripts
- Code organization and module structure

**Best Practices**:
- Follow consistent code style and conventions
- Write tests before or alongside implementation (TDD/BDD)
- Document complex logic with inline comments
- Keep configuration externalized and versioned
- Use type annotations where applicable

---

### 6. Validation

**Purpose**: The *enforcer* — ensures implementation matches the spec. Blocks drift and human error.

**Why It Matters**:
- Prevents breaking changes from reaching production
- Catches specification violations early in the CI pipeline
- Maintains data integrity and API consistency
- Reduces manual QA effort through automation

**Content Guidelines**:
- CI/CD pipeline configurations
- Contract testing scripts
- Linting rules and configurations
- Integration test suites
- Schema validation jobs
- Security scanning and audit jobs

**Best Practices**:
- Fail CI on specification violations
- Run validation jobs on every commit and PR
- Use automated code review tools
- Maintain validation job health dashboard
- Document validation failure remediation steps

---

### 7. Runbook

**Purpose**: The *operational manual* — how the system lives in production, scales, and recovers. Guides on-call engineers.

**Why It Matters**:
- Reduces Mean Time To Recovery (MTTR) for incidents
- Provides step-by-step guidance for common issues
- Documents scaling and deployment procedures
- Ensures operational knowledge is not siloed

**Content Guidelines**:
- Deployment procedures (manual and automated)
- Scaling instructions (horizontal/vertical)
- Backup and restore procedures
- Troubleshooting guides for common issues
- Runbook entries for specific error codes
- Contact information and escalation paths

**Best Practices**:
- Write runbooks for every P1/P2 incident
- Include exact commands and configuration snippets
- Test runbooks periodically (chaos engineering)
- Link runbook entries to relevant documentation
- Keep runbooks updated when system changes

---

## How to Use This Approach Effectively

### 1. Start with Requirements

Before writing any code or documentation, establish clear requirements. Ask:
- What business problem are we solving?
- How will we measure success?
- What are the non-negotiable constraints?

**Action**: Create a `docs/requirements/` directory and start with `PRD.md` and `KPIs.md`.

### 2. Define the Specification First

Once requirements are stable, define the technical specification. This becomes the contract for implementation.

**Action**: Create `docs/specification/` with `contract.yaml` (or appropriate format) and `error-codes.md`.

### 3. Design the Architecture

With requirements and specification in place, design the architecture. Document trade-off decisions explicitly.

**Action**: Create `docs/architecture/` with Mermaid diagrams and `trade-offs.md`.

### 4. Create Walkthroughs Early

As soon as the architecture is defined, create walkthroughs. This helps identify gaps and provides onboarding material.

**Action**: Create `docs/walkthrough/` with `TOUR.md` and sequence diagrams.

### 5. Implement with Validation in Mind

Write implementation code that adheres to the specification. Build validation into the CI pipeline from day one.

**Action**: Ensure test files are co-located with implementation and run on every commit.

### 6. Automate Validation

Build automated validation that runs in CI/CD. This ensures spec compliance and prevents drift.

**Action**: Configure CI jobs to validate against specification and block PRs on violations.

### 7. Document Operations from Day One

Create runbook entries as soon as deployment procedures are established. Update them when incidents occur.

**Action**: Create `docs/runbook/` with entries for deployment, scaling, and common issues.

---

## GitOps Integration

This documentation framework aligns with GitOps principles:

| GitOps Principle | Documentation Alignment |
|-----------------|------------------------|
| **Versioned** | All documentation lives in git, with history and audit trail |
| ** declarative** | Specifications and architecture are declarative contracts |
| **Automated** | Validation jobs automate spec compliance checks |
| **Self-Service** | Walkthroughs and runbooks enable self-service onboarding and operations |
| **Observability** | KPIs and metrics are defined for each documentation artifact |

**Git Structure**:
```
docs/
├── requirements/       # PRDs, user stories, KPIs
├── specification/      # OpenAPI, Protobuf, AsyncAPI specs
├── architecture/       # C4 diagrams, Mermaid, trade-off docs
├── walkthrough/        # TOUR.md, sequence diagrams
├── implementation/     # Source code (in src/)
├── validation/         # CI configs, test suites
└── runbook/            # Deployment, scaling, troubleshooting
```

---

## Metrics and Continuous Improvement

Each documentation artifact has associated KPIs. Track these to ensure quality:

| Document | KPI | Target |
|----------|-----|--------|
| Requirements | Requirement coverage | 100% of features have associated requirements |
| Specification | Spec compliance rate | 100% of messages validate against spec |
| Architecture | Decision documentation | 100% of major decisions logged with trade-offs |
| Walkthrough | New dev time-to-first-PR | <2 days from onboarding to first contribution |
| Implementation | Test coverage | >80% unit test coverage |
| Validation | Bypass rate | <1% of PRs bypass validation gates |
| Runbook | MTTR | <15 minutes for P1 incidents |

**Review Cadence**:
- Weekly: Review KPI dashboards and documentation gaps
- Monthly: Update documentation based on incident learnings
- Quarterly: Full framework review and improvement

---

## Template Examples

### Requirements Template
```markdown
# PRD: Feature Name

## Business Goal
[What problem are we solving?]

## Success Metrics
- [Metric 1]: Target [value]
- [Metric 2]: Target [value]

## User Stories
- As a [role], I want [feature] so that [benefit]
  - Acceptance Criteria: [details]

## Non-Functional Requirements
- Performance: [details]
- Security: [details]
- Scalability: [details]

## Out of Scope
- [What's explicitly excluded]
```

### Specification Template
```yaml
# contract.yaml
openapi: 3.0.0
info:
  title: NATSBridge API
  version: 1.0.0
paths:
  /api/v1/endpoint:
    post:
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/Request'
      responses:
        '200':
          description: Success
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Response'
```

### Architecture Template
```mermaid
%%{init: {'theme': 'base', 'themeVariables': {'primaryColor': '#3b82f6'}}}%%
flowchart TD
    A[Client] --> B[Caddy]
    B --> C[Node.js API]
    C --> D[Julia Worker]
    D --> E[NATS Cluster]
    E --> F[Storage]
    
    style A fill:#f9f9f9,stroke:#333
    style E fill:#e0e7ff,stroke:#3b82f6
```

### Runbook Template
```markdown
# Runbook: Service Restart

**Severity**: P2
**Estimated Time**: 5 minutes

## Symptoms
- Service is unresponsive
- Health checks are failing

## Steps
1. SSH to the host
2. Run: `kubectl rollout restart deployment/natsbridge`
3. Monitor: `kubectl get pods -l app=natsbridge -w`

## Rollback
- Run: `kubectl rollout undo deployment/natsbridge`

## Post-Incident
- [ ] Review logs for root cause
- [ ] Update runbook if needed
```

---

## Conclusion

This SDD + GitOps Documentation Framework ensures that documentation is:
- **Structured**: Seven distinct artifacts with clear purposes
- **Automated**: Validation and CI/CD integration
- **Versioned**: All documentation in git with history
- **Measurable**: KPIs for quality and effectiveness
- **Actionable**: Practical templates and examples

Use this framework as a living document—update it as your team's needs evolve.