2020-06-14 Ansible

Ansible Dynamic Inventory

Ansible Dynamic Inventory#

Dynamic inventory is useful when:

Inventory changes over time as hosts start and stop
Hosts need to be tracked from different sources

In those cases you probably have, or need, an external dynamic inventory system.

Ansible integrates with dynamic inventory in two ways:

Inventory plugins
Inventory scripts

Plugins are recommended over scripts.

Ansible Tower, now AWX or Red Hat Ansible Automation Platform, provides a GUI for handling dynamic inventory and syncing its inventory database with external inventory sources.

Run an ad hoc command#

You need to be able to SSH without a password.

ansible -i root@10.10.10.204, all -a 'uname -a'

To do this for multiple hosts:

ansible -i "root@10.10.10.93, root@10.10.10.92, root@10.200.1.94" all -a 'uptime'

To run a module for multiple hosts:

ansible -i "root@10.10.10.93, root@10.10.10.92, root@10.10.10.94" all -m setup

I have noticed that if one host requires a password, it will fail. If you set -k to ask for the SSH password, they all fail.

$ ansible -i "root@10.10.10.93, root@10.10.10.92, root@10.10.10.94" all -m setup
root@10.10.10.92 | UNREACHABLE! => {
    "changed": false,
    "msg": "Failed to connect to the host via ssh: root@10.10.10.92: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).\r\n",
    "unreachable": true
}

Ensure that Jenkins is started:

ansible -i "root@10.10.10.94," all -m service -a "name=jenkins state=started"

To use an inventory script with an ad hoc command:

ansible -i digital_ocean.py all -a 'uptime'

You can use the ansible-inventory utility to check the hosts visually:

ansible-inventory -i digital_ocean.py --list

Remember to ensure the inventory script is executable with chmod +x inventory_file.py

What dynamic inventory output should look like#

We want this inventory to know how to connect, so set the following variables:

ansible_connection=ssh
ansible_user=vagrant
ansible_host=10.0.0.1

We need to ensure that the _meta variable is set

It should look like this:

{
    "_meta": {
        "hostvars": {
            "host001": {
                "var001": "value"
            },
            "host002": {
                "var002": "value"
            }
        }
    }
}

If you intend to replace an existing static inventory file with an inventory script, it must return a JSON object with an all group that includes every host in the inventory as a member and every group in the inventory as a child.

{
    "_meta": {
        "hostvars": {}
    },
    "all": {
        "children": [
            "ungrouped"
        ]
    },
    "ungrouped": {
        "children": []
    }
}

Other variables we might want are:

Guest OS or distribution
Name
Networks

Inventory scripts#

You can run a Python script to get your hosts. This can be done by passing in the script as the inventory parameter: -i openstack_inventory.py

If you want to do this implicitly, remember that explicit is better than implicit.

You can place the script at /etc/ansible/hosts

There are existing integrations to check out as scripts for:

There are other existing inventory scripts

Or you can create your own inventory script

Using inventory directories and multiple inventory sources#

Using a directory can let Ansible use multiple inventories at the same time. This also allows mixing static and dynamic inventories.

Files ending in ~, .orig, .bak, .ini, .cfg, .retry, .pyc, .pyo will be ignored

Which you can change to your own with the inventory_ignore_extensions entry in ansible.cfg

More information is available in the documentation on multiple inventory sources.

Build a dynamic inventory#

In previous versions you had to create a script or program that could output JSON in the correct format when invoked with the proper arguments.

Inventory sources#

Inventory sources are what you pass to -i. They can be a path to a file, a script or the raw data for a plugin to use.

host list: comma-separated list of hosts
yaml: path to YAML format data file
constructed: path to YAML config file
ini: path to INI formatted data file
virtualbox: path to YAML config file
script plugin: path to executable outputting JSON

Ansible Dynamic Inventory