Build Your Inventory — Ansible Documentation

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# Build Your Inventory

Running a playbook without an inventory requires several command-line flags. Also, running a playbook against a single device is not a huge efficiency gain over making the same change manually. The next step to harnessing the full power of Ansible is to use an inventory file to organize your managed nodes into groups with information like the `ansible_network_os` and the SSH user. 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.

Topics

- Build Your Inventory
  - Basic Inventory
  - Add Variables to Inventory
  - Group Variables within Inventory
  - Variable Syntax
  - Group Inventory by Platform
  - Protecting Sensitive Variables with `ansible-vault`

## 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.

    [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.

    [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:

    [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:

    [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:

    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 will show you how to encrypt a single SSH password. 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. It is used as the encryption key, and with this you can encrypt dozens of different passwords across your Ansible project. You can access all those secrets (encrypted values) 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:

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

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

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

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

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

and type in the vault password for `my_user`.

The `--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`:

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

This is an example using an extract from a YAML inventory, as the INI format does not support inline vaults:

    ...

    vyos: # this is a group in yaml inventory, but you can also do under a host
      vars:
        ansible_connection: network_cli
        ansible_network_os: vyos
        ansible_user: my_vyos_user
        ansible_password:  !vault |
             $ANSIBLE_VAULT;1.2;AES256;my_user
             66386134653765386232383236303063623663343437643766386435663632343266393064373933
             3661666132363339303639353538316662616638356631650a316338316663666439383138353032
             63393934343937373637306162366265383461316334383132626462656463363630613832313562
             3837646266663835640a313164343535316666653031353763613037656362613535633538386539
             65656439626166666363323435613131643066353762333232326232323565376635

     ...

To use an inline vaulted variables with an INI inventory you need to store it in a ‘vars’ file in YAML format, it can reside in host_vars/ or group_vars/ to be automatically picked up or referenced from a play via `vars_files` or `include_vars`.

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

    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:

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

To see the original value, you can use the debug module. Please note if your YAML file defines the ansible_connection variable (as we used in our example), it will take effect when you execute the command below. To prevent this, please make a copy of the file without the ansible_connection variable.

    cat vyos.yml | grep -v ansible_connection >> vyos_no_connection.yml

    ansible localhost -m debug -a var="ansible_password" -e "@vyos_no_connection.yml" --ask-vault-pass
    Vault password:

    localhost | SUCCESS => {
        "ansible_password": "VyOS_SSH_password"
    }

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 the introduction to inventory; for more details on ansible-vault, see the full Ansible Vault documentation.

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