Ansible Inventory Settings

Ansible Inventory Settings#

Ansible uses an inventory to manage hosts in your infrastructure. The inventory lists information about target hosts, like their IP addresses or Fully Qualified Domain Names (FQDNs). The default inventory file is located at /etc/ansible/hosts, but you can specify a different file using the -i <path> option or in the configuration with inventory.

Formats for Inventory Files#

You can create inventory files in different formats, with INI and YAML being the most common. Here are examples based on a lab setup:

INI Format#

A basic INI format might look like this:

[router]
172.16.10.11

[core]
172.16.10.12

[switch]
172.16.10.13
172.16.10.14

The names in brackets are group names. They help classify hosts so you can manage specific sets of hosts easily.

You can also use DNS names instead of IP addresses:

[router]
r1

[core]
core-sw

[switch]
access1
access2

Ensure your DNS settings can resolve these names to the correct IP addresses.

YAML Format#

Here’s how the same inventory looks in YAML format:

all:
  children:
    router:
      hosts:
        172.16.10.11:
    core:
      hosts:
        172.16.10.12:
    switch:
      hosts:
        172.16.10.13:
        172.16.10.14:

In this format, all is the top-level group containing all hosts and groups. The hosts key lists each host, and children contains subgroups like router, core, and switch.

Ansible includes two default groups: all, which targets all hosts, and ungrouped, which contains hosts not in any other group.

Defining Host Aliases#

You can define aliases for hosts to make them easier to reference:

core-sw ansible_host=172.16.10.12

Inventory and Variables#

Ansible allows setting variables in the inventory to control behavior and manage hosts more effectively.

Host Variables#

You can define variables for each host:

[router]
r1 ansible_host=172.16.10.11 ansible_user=bob

[core]
core-sw ansible_host=172.16.10.12 ansible_user=joe

Group Variables#

Variables can also be set at the group level:

[router]
r1 ansible_host=172.16.10.11 ansible_user=bob ansible_password=bob123

[core]
core-sw ansible_host=172.16.10.12 ansible_user=joe ansible_password=joe123

[campus:children]
router
core

[campus:vars]
ansible_network_os=ios
ansible_connection=network_cli

Although you can set variables in the inventory, it’s usually better to store them in separate host and group variable files. This helps keep your project organized and clear.

Create folders named group_vars and host_vars in the same directory as your inventory file to store these variable files. For example, group_vars/campus.yaml might look like this:

---
# group_vars/campus.yaml
ansible_user: admin
ansible_password: cisco
ansible_network_os: ios
ansible_connection: network_cli

Viewing Inventory Information#

Use the following command to view your inventory structure:

ansible-inventory -i inventory.yaml --graph

This command shows the group hierarchy and the hosts in each group. To view details about a specific host, use:

ansible-inventory -i inventory.yaml --host r1

Key Points About Inventory#

  1. Host Information: Inventory files contain crucial information about target hosts.

  2. Default Location: The default inventory file is at /etc/ansible/hosts.

  3. File Format: Inventory files can be in INI or YAML format.

  4. Grouping Hosts: Group names classify hosts based on common attributes or roles.

  5. Special Groups: Groups like campus can categorize network devices.

  6. Default Groups: all includes every host, and ungrouped includes hosts not in other groups.

Using the inventory helps you organize and manage your infrastructure efficiently, making automation tasks with Ansible easier and more effective.

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