Ansible Architecture Documentation

This directory contains comprehensive architecture documentation for Ansible Core, including system design, component relationships, and execution flows.

Documents Overview

Core Architecture

• architecture-overview.md - High-level system architecture and design principles
• execution-engine.md - Core execution engine components and task flow
• plugin-system.md - Plugin architecture and extensibility mechanisms
• playbook-processing.md - Playbook parsing and execution pipeline
• inventory-variables.md - Inventory management and variable resolution

Component Diagrams

• diagrams/ - Mermaid diagrams showing system relationships and data flows

Key Architectural Patterns

1. Multi-Process Execution

Ansible uses a master-worker pattern with isolated execution environments:

• TaskQueueManager orchestrates execution
• WorkerProcess instances execute tasks in isolation
• FinalQueue handles inter-process communication

2. Plugin-Based Extensibility

The system achieves modularity through 15+ plugin types:

• Action/Module Plugins - Task execution
• Connection Plugins - Host connectivity
• Strategy Plugins - Execution flow control
• Callback Plugins - Event handling and output

3. Variable Resolution Hierarchy

Complex variable precedence system with 13 levels:

• Role defaults → Group variables → Host variables → Facts → Extra variables
• Configurable precedence rules for different use cases

4. Template-Driven Configuration

Jinja2 integration with:

• Context-aware templating
• Lazy evaluation for performance
• Trust-based security model

Design Principles

1. Idempotency - Operations can be safely repeated
2. Declarative - Users describe desired state, not procedures
3. Agentless - No software installed on managed nodes
4. Extensible - Plugin architecture enables customization
5. Scalable - Multi-process execution and efficient caching

Development Guidelines

• Follow established patterns when extending functionality
• Use appropriate plugin types for new features
• Maintain backward compatibility in public APIs
• Include comprehensive test coverage for new components
• Document architectural decisions and trade-offs

Getting Started

For developers new to the Ansible codebase:

1. Start with architecture-overview.md for the big picture
2. Read execution-engine.md to understand task execution
3. Review plugin-system.md for extensibility patterns
4. Examine specific components based on your development needs

Contributing

When adding new architectural documentation:

1. Follow the established structure and format
2. Include both prose explanations and visual diagrams
3. Focus on relationships and data flow between components
4. Provide concrete examples where helpful
5. Update this README when adding new documents