Example 10

hosts.py

#!/bin/env python

import json
import argparse

class SampleInventory:

    HOSTS = [
        {
            "host": "provisioner",
            "vars": {
                'ansible_connection': 'local'
            }
        },
        {
            "host": "centos1",
            "vars": {
                "ansible_host": "192.168.77.22",
                "ansible_port": 2345
            }
        },
        {
            "host": "ubuntu1",
            "vars": {
                "ansible_host": "192.168.77.23"
            }
        }
    ]

    GROUPS = [
        {
            "name": "centos",
            "hosts": ["provisioner", "centos1"],
            "vars": {
                "ansible_become": True
            }
        },
        {
            "name": "ubuntu",
            "hosts": ["ubuntu1"]
        }
    ]

    def generate_response(self, parser):
        args = parser.parse_args()
        if args.list and args.host is None:
            self.get_list()
        elif not args.list and args.host:
            self.get_host(args.host)
        else:
            parser.print_help()

    def get_host(self, host):
        try:
            host_data = [x for x in self.HOSTS if x["host"] == host][0]
            print(json.dumps(host_data["vars"], indent=4))
        except IndexError as e:
            raise IndexError('Host not found.')

    def get_list(self):
        inventory = {}
        meta = self.create_meta()
        groups = self.create_groups()
        inventory.update(meta)
        inventory.update(groups)
        print(json.dumps(inventory, indent=4))

    def create_meta(self):
        meta = {
            "_meta": {
                "hostvars": {}
            }
        }
        for host in self.HOSTS:
            all_vars = {}
            host_hostvars = host["vars"]
            host_groupvars = self.get_host_groupvars(host)
            all_vars.update(host_hostvars)
            all_vars.update(host_groupvars)
            meta["_meta"]["hostvars"][host["host"]] = all_vars
        return meta

    def get_host_groupvars(self, host):
        group_vars = {}
        for group in self.GROUPS:
            if host["host"] in group["hosts"]:
                try:
                    group_vars.update(group["vars"])
                except KeyError:
                    pass
        return group_vars

    def create_groups(self):
        groups = {
            "all": {
                "children": ["ungrouped"]
            }
        }
        for group in self.GROUPS:
            groups[group["name"]] = group["hosts"]
            groups["all"]["children"].append(group["name"])
        return groups

if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('--list', action = 'store_true')
    parser.add_argument('--host')
    SampleInventory().generate_response(parser)

Tip

Dynamic inventories can be extremely useful especially when you want to create an inventory from another file (eg. Terraform output). They can be written in any programming language provided that they are executables that generate the correct ouput and accept the --list flag.

Compare the outputs of the following commands

python hosts.py --list
ansible-inventory --list

Try to execute the whoami command on all hosts.

ansible all -m command -a "whoami"

Bonus round

Create a Bash script that will act as an Ansible inventory. Use the output of ansible-inventory --list to hardcode the data or call hosts.py from within the script.