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Ansible-cmdb is designed with a modular architecture that separates concerns into distinct components. This guide explains how these components work together to transform Ansible fact data into various output formats.

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High-Level Architecture

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Core Components

Ansible-cmdb consists of four main Python modules:

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ansible.py - Main Orchestrator

The Ansible class is the central component responsible for gathering and managing all host information. Key Responsibilities:
  • Parsing fact directories containing JSON output from Ansible’s setup module
  • Processing inventory files (static hosts files and dynamic inventory scripts)
  • Parsing host_vars and group_vars directories
  • Managing the complete host information dictionary
  • Applying limits to filter hosts
Main Workflow:
1

Initialization

The Ansible object is instantiated with paths to fact directories and optional inventory paths.
2

Fact Parsing

For each fact directory, _parse_fact_dir() is called to read JSON files containing host facts gathered by Ansible’s setup module.
3

Inventory Scanning

If inventory paths are provided (-i option), the system scans for:
  • Static hosts files (parsed by HostsParser)
  • Dynamic inventory scripts (executable files)
  • Directory structures containing multiple inventory files
4

Variable Collection

The system scans for and applies:
  • Host-specific variables from host_vars/ directories
  • Group variables from group_vars/ directories
5

Deep Update

All information is merged using the update_host() method, which performs deep dictionary updates to overlay facts, variables, and inventory data.
Key Methods:
  • update_host(hostname, key_values, overwrite=True) - Deep-updates host information
  • get_hosts() - Returns the final list of hosts with limits applied
  • hosts_in_group(groupname) - Returns hosts belonging to a specific group

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parser.py - Inventory Parser

The parser module contains classes for parsing different inventory formats.

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HostsParser

Parses Ansible hosts inventory files and generates a dictionary of hosts with their groups and variables. Parsing Process:
  1. Section Identification: Identifies sections in the inventory file:
    • [groupname] - Regular host groups
    • [groupname:children] - Parent groups
    • [groupname:vars] - Group variables
  2. Host Expansion: Supports Ansible’s host pattern syntax: 
    web[01:10].example.com  # Expands to web01-web10
db[a:c].example.com     # Expands to dba, dbb, dbc
  3. Variable Application: Applies variables from:
    • Inline host variables: host1 ansible_port=2222
    • Group variables from :vars sections
    • Parent group memberships from :children sections
Key Methods:
  • expand_hostdef(hostdef) - Expands host patterns into individual hostnames
  • _parse_line_entry(line, type) - Parses individual inventory lines
  • _apply_section(section, hosts) - Applies section data to hosts

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DynInvParser

Parses JSON output from dynamic inventory scripts. Features:
  • Handles the _meta section for host variables
  • Processes group definitions with hosts and vars
  • Supports both dict and list formats for group definitions

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render.py - Template Renderer

The Render class is a wrapper that facilitates template rendering using Mako or Python-based templates. Template Types:
  1. Mako Templates (.tpl files):
    • Used for most output formats (HTML, CSV, Markdown, etc.)
    • Supports template inheritance and includes
    • Full access to host data and custom variables
  2. Python Templates (.py files):
    • Executable Python scripts for complex rendering logic
    • Used for formats like html_fancy_split and markdown_split
    • Must implement a render(hosts, vars, tpl_dirs) function
Rendering Process:
1

Template Discovery

Searches for templates in specified directories:
  • Direct file path if provided
  • {template_name}.tpl in template directories
  • {template_name}.py in template directories
2

Template Loading

Loads the template with proper Mako configuration:
  • UTF-8 encoding for input and output
  • Error replacement for encoding issues
  • Template lookup for includes
3

Rendering

Executes the template with:
  • hosts - Dictionary of all host data
  • Custom variables passed via -p option

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util.py - Utility Functions

Provides helper functions used throughout the codebase: Key Functions:
  • deepupdate(target, src, overwrite=True) - Recursively merges dictionaries, lists, and sets. This is crucial for combining data from multiple sources (facts, inventory, host_vars, group_vars).
  • is_executable(path) - Determines if a file is executable, used to identify dynamic inventory scripts.
  • find_path(dirs, path_to_find) - Searches for a file across multiple directories.
  • to_bool(s) - Converts string values to boolean.
Deep Update Behavior: 
# Lists are extended
t = {'hobbies': ['programming']}
deepupdate(t, {'hobbies': ['gaming']})
# Result: {'hobbies': ['programming', 'gaming']}

# Dicts are recursively merged
t = {'config': {'debug': True}}
deepupdate(t, {'config': {'verbose': True}})
# Result: {'config': {'debug': True, 'verbose': True}}

# Sets are updated
t = {'groups': {'web', 'prod'}}
deepupdate(t, {'groups': {'monitoring'}})
# Result: {'groups': {'web', 'prod', 'monitoring'}}

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Data Flow

Here’s how data flows through ansible-cmdb:

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Extension Points

Ansible-cmdb is designed to be extensible:

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Custom Templates

Create your own output formats by writing:
  • Mako templates for simple text-based formats
  • Python templates for complex multi-file outputs
Templates have access to:
  • hosts - Complete host data dictionary
  • Custom parameters passed via -p key=value

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Custom Facts

Extend host information by:
  1. Creating additional JSON files in a separate directory
  2. Passing the directory to ansible-cmdb alongside fact directories
  3. Data is automatically merged with existing host information

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Dynamic Inventory

Integrate with external systems using dynamic inventory scripts that output JSON in Ansible’s format.

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File Organization

src/ansiblecmdb/
├── __init__.py          # Package initialization
├── ansible.py           # Main Ansible class
├── parser.py            # Inventory parsers
├── render.py            # Template renderer
├── util.py              # Utility functions
├── ihateyaml.py         # YAML parser wrapper
└── data/
    ├── tpl/             # Built-in templates
    │   ├── html_fancy.tpl
    │   ├── html_fancy_split.py
    │   ├── csv.tpl
    │   ├── markdown.tpl
    │   └── ...
    └── static/          # Static assets (CSS, JS)

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Dependencies

Ansible-cmdb relies on these key Python packages:
  • Mako - Template engine for generating output
  • PyYAML - Parsing YAML files (host_vars, group_vars)
  • ushlex - Unicode-aware shell lexer for Python 2
  • jsonxs - JSON parsing with additional features

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Source Code

The ansible-cmdb source code is available on GitHub: https://github.com/fboender/ansible-cmdb For more details on contributing and development, see the Contributing Guide.

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