fifteen-factor-app

# Fifteen-Factor App Methodology

## Overview

The Fifteen-Factor App methodology extends the original Twelve-Factor App principles (created by Heroku in 2012) with three additional factors essential for modern cloud-native applications: API First, Telemetry, and Security.

This methodology provides architectural principles and guidelines for building software-as-a-service applications that are:

- **Performant** - Optimised for speed and efficiency
- **Scalable** - Designed for horizontal scaling without significant changes
- **Manageable** - Easy to deploy, monitor, and maintain
- **Resilient** - Robust against failures with graceful degradation

## When to Apply This Methodology

Apply the Fifteen-Factor principles during:

1. **Architecture Planning** - When designing new applications or microservices
2. **PRP/PRD Creation** - When documenting technical requirements and specifications
3. **Code Reviews** - When evaluating whether implementations follow best practices
4. **Migration Planning** - When modernising legacy applications for cloud deployment
5. **Technical Debt Assessment** - When identifying architectural improvements

## The Fifteen Factors at a Glance

| Factor | Principle | Key Concept |
|--------|-----------|-------------|
| I. Codebase | One codebase, many deploys | Single repo per app, version controlled |
| II. Dependencies | Explicitly declare and isolate | No implicit system-wide packages |
| III. Config | Store in environment | Never hardcode configuration |
| IV. Backing Services | Treat as attached resources | Databases, caches are swappable resources |
| V. Build, Release, Run | Strict separation | Immutable releases, no runtime changes |
| VI. Processes | Stateless and share-nothing | Horizontal scaling, no sticky sessions |
| VII. Port Binding | Export via port | Self-contained, no runtime injection |
| VIII. Concurrency | Scale out via process model | Horizontal over vertical scaling |
| IX. Disposability | Fast startup, graceful shutd