DevOps Classroom Series – 24/Oct/2021

Ansible Dynamic Inventory

• Ansible Dynamic inventory is a script in any language which when called with argument
  • –list: should return something like

    {
        "group001": {
            "hosts": ["host001", "host002"],
            "vars": {
                "var1": true
            },
            "children": ["group002"]
        },
        "group002": {
            "hosts": ["host003","host004"],
            "vars": {
                "var2": 500
            },
            "children":[]
        },
        "_meta": {
            "hostvars": {
  
            }
        }
  
    }
  

  • –host <hostname>: should return

    {
        "VAR001": "VALUE",
        "VAR002": "VALUE",
    }
  

• So look into this example for dummy inventory

#!/usr/bin/env python3
import os
import sys
import argparse
import json


def read_cli_args():
    """
    This method is used to read the command line args

    Returns
        args
    """
    parser = argparse.ArgumentParser()
    parser.add_argument("--list", action='store_true')
    parser.add_argument("--host", action='store')
    args = parser.parse_args()
    return args

def example_list():
    """
    This method will return the example list
    """
    return {
        'group': {
            'hosts': ['localhost', '172.31.17.152', '172.31.29.133'],
            'vars': {
                'message': 'hello'
            }
        },
        '_meta': {
            'hostvars': {}
        }
    }

def empty_inventory():
    return { '_meta': { 'hostvars': {} }}

if __name__ == '__main__':
    args = read_cli_args()
    if args.list:
        print(json.dumps(example_list()))
    else:
        print(json.dumps(empty_inventory()))

• Ansible expects inventory to be executable file.

Ansible Parallelism

• Ansible establishes parallel connection with node which is called as fork.
• By default ansible uses 5 forks
• We can set the default number of forks in /etc/ansible/ansible.cfg file

[defaults]
forks = 50

• We can also set number of forks by passing -f with ansible-playbook and ansible command line

ansible-playbook -i hosts play.yml -f 100
ansible -f 1 -m ping all