infrastructure-documenter

What this skill does

# Infrastructure Documenter Skill

## Overview

This skill helps you create clear, maintainable infrastructure documentation. Covers architecture diagrams, runbooks, system documentation, operational procedures, and documentation-as-code practices.

## Documentation Philosophy

### Principles
1. **Living documentation**: Keep it in sync with reality
2. **Audience-aware**: Different docs for different readers
3. **Actionable**: Every doc should help someone do something
4. **Version-controlled**: Documentation changes tracked with code

### Document Types

| Type | Audience | Purpose |
|------|----------|---------|
| Architecture | Engineers | Understand system design |
| Runbooks | Ops/SRE | Handle incidents |
| API Docs | Developers | Integrate with system |
| Onboarding | New hires | Get up to speed |
| Decision Records | Future you | Understand why |

## Architecture Documentation

### System Architecture Overview

```markdown
# System Architecture

## Overview

[Project Name] is a [type] application that [purpose].

## High-Level Architecture

```
┌─────────────────────────────────────────────────────────────┐
│                        Users                                 │
└─────────────────────────────────────────────────────────────┘
                              │
                              ▼
┌─────────────────────────────────────────────────────────────┐
│                      Vercel Edge                             │
│  ┌─────────────────┐  ┌─────────────────┐                   │
│  │   Next.js App   │  │  Edge Functions │                   │
│  └─────────────────┘  └─────────────────┘                   │
└─────────────────────────────────────────────────────────────┘
                              │
              ┌───────────────┼───────────────┐
              ▼               ▼               ▼
┌─────────────────┐ ┌─────────────────┐ ┌─────────────────┐
│    Supabase     │ │      Redis      │ │    Stripe       │
│  - PostgreSQL   │ │  - Session      │ │  - Payments     │
│  - Auth         │ │  - Cache        │ │  - Webhooks     │
│  - Realtime     │ │                 │ │                 │
│  - Storage      │ │                 │ │                 │
└─────────────────┘ └─────────────────┘ └─────────────────┘
```

## Components

### Frontend (Next.js App)
- **Location**: Vercel Edge Network
- **Framework**: Next.js 14 (App Router)
- **Styling**: Tailwind CSS + shadcn/ui
- **State**: Zustand + React Query

### Backend Services
| Service | Provider | Purpose |
|---------|----------|---------|
| Database | Supabase | PostgreSQL with RLS |
| Auth | Supabase Auth | User authentication |
| Storage | Supabase Storage | File uploads |
| Cache | Upstash Redis | Session & API cache |
| Payments | Stripe | Subscriptions |
| Email | Resend | Transactional emails |

### Data Flow

1. User request → Vercel Edge
2. SSR/API Route processes request
3. Database queries via Supabase client
4. Response cached at edge (when applicable)
5. Response returned to user

## Security

### Authentication Flow
1. User signs in via Supabase Auth
2. JWT token issued and stored in cookie
3. Server validates token on each request
4. RLS policies enforce data access

### Data Protection
- All data encrypted at rest (AES-256)
- TLS 1.3 for data in transit
- Secrets stored in Vercel environment
- PII fields encrypted in database
```

### Mermaid Diagrams

```markdown
## Request Flow

```mermaid
sequenceDiagram
    participant U as User
    participant V as Vercel
    participant N as Next.js
    participant S as Supabase
    participant R as Redis

    U->>V: HTTPS Request
    V->>N: Route to App

    alt Cached Response
        N->>R: Check Cache
        R-->>N: Cache Hit
        N-->>U: Return Cached
    else Cache Miss
        N->>S: Query Database
        S-->>N: Data
        N->>R: Store in Cache
        N-->>U: Return Response
    end
```

## Database Schema

```mermaid
erDiagram
    users ||--o{ projects : owns
    users {
        uuid id PK
        text email
        text name
        timestamp created_at
    }
    projects ||--o{ tasks : contains
    projects {
        uuid id PK
        uuid user_id FK
        text name
        text status
    }
    tasks {
        uuid id PK
        uuid project_id FK
        text title
        boolean completed
    }
```
```

## Runbooks

### Runbook Template

```markdown
# Runbook: [Service Name] - [Issue Type]

## Overview
Brief description of the issue and when this runbook applies.

## Severity
- **P1 (Critical)**: Complete outage
- **P2 (High)**: Degraded service
- **P3 (Medium)**: Minor impact
- **P4 (Low)**: No user impact

## Detection
How this issue is typically detected:
- [ ] Alert from [monitoring system]
- [ ] User report
- [ ] Automated check failure

## Impact Assessment
- **Users affected**: All / Segment / None
- **Data at risk**: Yes / No
- **Revenue impact**: High / Medium / Low / None

## Prerequisites
- [ ] Access to [system/dashboard]
- [ ] Credentials for [service]
- [ ] Contact info for [team/person]

## Resolution Steps

### Step 1: Verify the Issue
```bash
# Check service status
curl -I https://api.example.com/health

# Check logs
vercel logs --follow
```

### Step 2: Identify Root Cause
Common causes:
- [ ] Database connection pool exhausted
- [ ] Memory limit reached
- [ ] External service down
- [ ] Bad deployment

### Step 3: Apply Fix

#### If Database Issue:
```bash
# Check connection count
SELECT count(*) FROM pg_stat_activity;

# Kill idle connections
SELECT pg_terminate_backend(pid)
FROM pg_stat_activity
WHERE state = 'idle' AND query_start < now() - interval '1 hour';
```

#### If Bad Deployment:
```bash
# Rollback to previous deployment
vercel rollback
```

### Step 4: Verify Fix
```bash
# Check service health
curl https://api.example.com/health

# Monitor error rates for 15 minutes
```

## Escalation
If unable to resolve within 30 minutes:
1. Page on-call engineer: [contact]
2. Notify stakeholders in #incidents
3. Update status page

## Post-Incident
- [ ] Create incident report
- [ ] Schedule post-mortem (P1/P2 only)
- [ ] Update this runbook if needed

## Related Links
- [Dashboard](https://dashboard.example.com)
- [Logs](https://logs.example.com)
- [Metrics](https://metrics.example.com)
```

### Database Runbooks

```markdown
# Runbook: Database Performance Issues

## Symptoms
- Slow API responses (>1s)
- Timeout errors in logs
- High database CPU in dashboard

## Quick Checks

### 1. Check Active Connections
```sql
SELECT
  state,
  count(*),
  max(now() - query_start) as max_duration
FROM pg_stat_activity
GROUP BY state;
```

### 2. Find Long-Running Queries
```sql
SELECT
  pid,
  now() - query_start AS duration,
  query
FROM pg_stat_activity
WHERE state = 'active'
  AND now() - query_start > interval '30 seconds'
ORDER BY duration DESC;
```

### 3. Check Table Sizes
```sql
SELECT
  schemaname,
  tablename,
  pg_size_pretty(pg_total_relation_size(schemaname || '.' || tablename)) as size
FROM pg_tables
WHERE schemaname = 'public'
ORDER BY pg_total_relation_size(schemaname || '.' || tablename) DESC
LIMIT 10;
```

### 4. Check Missing Indexes
```sql
SELECT
  relname,
  seq_scan,
  idx_scan,
  seq_scan - idx_scan AS difference
FROM pg_stat_user_tables
WHERE seq_scan > idx_scan
ORDER BY difference DESC;
```

## Resolution

### Kill Problematic Queries
```sql
SELECT pg_terminate_backend(pid)
FROM pg_stat_activity
WHERE pid = [PID_FROM_ABOVE];
```

### Add Missing Index
```sql
CREATE INDEX CONCURRENTLY idx_table_column
ON table_name (column_name);
```
```

## Decision Records (ADRs)

### ADR Template

```markdown
# ADR-001: Choose Supabase for Database

## Status
Accepted

## Context
We need a database solution for [Project Name] that supports:
- PostgreSQL compatibility
- Real-time subscriptions
- Built-in authentication
- Easy local development
- Generous free tier

## Decision
We will use Supabase as our primary database and auth provider.

## Alternatives Considered

### PlanetScale
**Pros: