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Build Your Inventory
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A fully-featured inventory file can serve as the source of truth for your network. Using an inventory file, a single playbook can maintain hundreds of network devices with a single command. This page shows you how to build an inventory file, step by step.

.. contents:: Topics

Basic Inventory
==================================================

First, group your inventory logically. Best practice is to group servers and network devices by their What (application, stack or microservice), Where (datacenter or region), and When (development stage):

- **What**: db, web, leaf, spine
- **Where**: east, west, floor_19, building_A
- **When**: dev, test, staging, prod

Avoid spaces, hyphens, and preceding numbers (use ``floor_19``, not ``19th_floor``) in your group names. Group names are case sensitive.

This tiny example data center illustrates a basic group structure. You can group groups using the syntax ``[metagroupname:children]`` and listing groups as members of the metagroup. Here, the group ``network`` includes all leafs and all spines; the group ``datacenter`` includes all network devices plus all webservers.

.. code-block:: yaml

   [leafs]
   leaf01
   leaf02

   [spines]
   spine01
   spine02

   [network:children]
   leafs
   spines

   [webservers]
   webserver01
   webserver02

   [datacenter:children]
   network
   webservers


Add Variables to Inventory
================================================================================

Next, you can set values for many of the variables you needed in your first Ansible command in the inventory, so you can skip them in the ansible-playbook command. In this example, the inventory includes each network device's IP, OS, and SSH user. If your network devices are only accessible by IP, you must add the IP to the inventory file. If you access your network devices using hostnames, the IP is not necessary. 

.. code-block:: yaml

   [leafs]
   leaf01 ansible_host=10.16.10.11 ansible_network_os=vyos ansible_user=my_vyos_user
   leaf02 ansible_host=10.16.10.12 ansible_network_os=vyos ansible_user=my_vyos_user

   [spines]
   spine01 ansible_host=10.16.10.13 ansible_network_os=vyos ansible_user=my_vyos_user
   spine02 ansible_host=10.16.10.14 ansible_network_os=vyos ansible_user=my_vyos_user

   [network:children]
   leafs
   spines

   [servers]
   server01 ansible_host=10.16.10.15 ansible_user=my_server_user
   server02 ansible_host=10.16.10.16 ansible_user=my_server_user

   [datacenter:children]
   leafs
   spines
   servers

Group Variables within Inventory
================================================================================

When devices in a group share the same variable values, such as OS or SSH user, you can reduce duplication and simplify maintenance by consolidating these into group variables:

.. code-block:: yaml

   [leafs]
   leaf01 ansible_host=10.16.10.11
   leaf02 ansible_host=10.16.10.12

   [leafs:vars]
   ansible_network_os=vyos
   ansible_user=my_vyos_user

   [spines]
   spine01 ansible_host=10.16.10.13
   spine02 ansible_host=10.16.10.14

   [spines:vars]
   ansible_network_os=vyos
   ansible_user=my_vyos_user

   [network:children]
   leafs
   spines

   [servers]
   server01 ansible_host=10.16.10.15
   server02 ansible_host=10.16.10.16

   [datacenter:children]
   leafs
   spines
   servers

Variable Syntax
================================================================================

The syntax for variable values is different in inventory, in playbooks and in ``group_vars`` files, which are covered below. Even though playbook and ``group_vars`` files are both written in YAML, you use variables differently in each. 

- In an ini-style inventory file you **must** use the syntax ``key=value`` for variable values: ``ansible_network_os=vyos``. 
- In any file with the ``.yml`` or ``.yaml`` extension, including playbooks and ``group_vars`` files, you **must** use YAML syntax: ``key: value``

  - In ``group_vars`` files, use the full ``key`` name: ``ansible_network_os: vyos``. 
  - In playbooks, use the short-form ``key`` name, which drops the ``ansible`` prefix: ``network_os: vyos``


Group Inventory by Platform
================================================================================

As your inventory grows, you may want to group devices by platform. This allows you to specify platform-specific variables easily for all devices on that platform:

.. code-block:: yaml

   [vyos_leafs]
   leaf01 ansible_host=10.16.10.11
   leaf02 ansible_host=10.16.10.12

   [vyos_spines]
   spine01 ansible_host=10.16.10.13
   spine02 ansible_host=10.16.10.14

   [vyos:children]
   vyos_leafs
   vyos_spines

   [vyos:vars]
   ansible_connection=network_cli
   ansible_network_os=vyos
   ansible_user=my_vyos_user

   [network:children]
   vyos

   [servers]
   server01 ansible_host=10.16.10.15
   server02 ansible_host=10.16.10.16

   [datacenter:children]
   vyos
   servers

With this setup, you can run first_playbook.yml with only two flags:

.. code-block:: bash

   ansible-playbook -i inventory -k first_playbook.yml

With the ``-k`` flag, you provide the SSH password(s) at the prompt. Alternatively, you can store SSH and other secrets and passwords securely in your group_vars files with ``ansible-vault``. 


Protecting Sensitive Variables with ``ansible-vault`` 
================================================================================

The ``ansible-vault`` command provides encryption for files and/or individual variables like passwords. This tutorial uses SSH passwords for an example. You can use the commands below to encrypt other sensitive information, such as database passwords, privilege-escalation passwords and more.

First you must create a password for ansible-vault itself. Then you can encrypt dozens of different passwords across your Ansible project. You can access all those secrets with a single password (the ansible-vault password) when you run your playbooks. Here's a simple example.

Create a file and write your password for ansible-vault to it:

.. code-block:: bash

   echo "my-ansible-vault-pw" > ~/my-ansible-vault-pw-file

Encrypt the ssh password for your VyOS network devices, pulling your ansible-vault password from the file you just created:

.. code-block:: bash

   ansible-vault encrypt_string --vault-id my_user@~/my-ansible-vault-pw-file 'VyOS_SSH_password' --name 'ansible_ssh_pass'

If you prefer to type your vault password rather than store it in a file, you can request a prompt:

.. code-block:: bash

   ansible-vault encrypt_string --vault-id my_user@prompt 'VyOS_SSH_password' --name 'ansible_ssh_pass'

and type in the vault password for ``my_user``. 

The :option:`--vault-id <ansible-playbook --vault-id>` flag allows different vault passwords for different users or different levels of access. The output includes the user name ``my_user`` from your ``ansible-vault`` command and uses the YAML syntax ``key: value``:

.. code-block:: bash

   ansible_ssh_pass: !vault |
          $ANSIBLE_VAULT;1.2;AES256;my_user
          66386134653765386232383236303063623663343437643766386435663632343266393064373933
          3661666132363339303639353538316662616638356631650a316338316663666439383138353032
          63393934343937373637306162366265383461316334383132626462656463363630613832313562
          3837646266663835640a313164343535316666653031353763613037656362613535633538386539
          65656439626166666363323435613131643066353762333232326232323565376635
   Encryption successful

Copy this output into your inventory file under ``[vyos:vars]``, which now looks like this:

.. code-block:: yaml

   [vyos:vars]
   ansible_connection=network_cli
   ansible_network_os=vyos
   ansible_user=my_vyos_user
   ansible_ssh_pass= !vault |
          $ANSIBLE_VAULT;1.2;AES256;my_user
          66386134653765386232383236303063623663343437643766386435663632343266393064373933
          3661666132363339303639353538316662616638356631650a316338316663666439383138353032
          63393934343937373637306162366265383461316334383132626462656463363630613832313562
          3837646266663835640a313164343535316666653031353763613037656362613535633538386539
          65656439626166666363323435613131643066353762333232326232323565376635

To run a playbook with this setup, drop the ``-k`` flag and add a flag for your ``vault-id``:

.. code-block:: bash

   ansible-playbook -i inventory --vault-id my_user@~/my-ansible-vault-pw-file first_playbook.yml

Or with a prompt instead of the vault password file:

.. code-block:: bash

   ansible-playbook -i inventory --vault-id my_user@prompt first_playbook.yml


.. warning::
   
   Vault content can only be decrypted with the password that was used to encrypt it. If you want to stop using one password and move to a new one, you can update and re-encrypt existing vault content with ``ansible-vault rekey myfile``, then provide the old password and the new password. Copies of vault content still encrypted with the old password can still be decrypted with old password.

For more details on building inventory files, see :doc:`the introduction to inventory<../../user_guide/intro_inventory>`; for more details on ansible-vault, see :doc:`the full Ansible Vault documentation<../../user_guide/vault>`.

Now that you understand the basics of commands, playbooks, and inventory, it's time to explore some more complex Ansible Network examples. 
