Inventory

The inventory is the foundation of Ansible automation --- it defines which hosts Ansible manages and how they are organised. Without an inventory, Ansible has no targets to act upon.

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What is an Inventory?

An inventory is a file (or script) that lists the managed nodes (hosts) and organises them into groups. Ansible reads the inventory to determine which hosts to target when running commands or playbooks.

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Static Inventory

The simplest inventory format is a static INI file:

INI Format

# inventory

[webservers]
web1.example.com
web2.example.com
web3.example.com

[dbservers]
db1.example.com
db2.example.com

[loadbalancers]
lb1.example.com

YAML Format

The same inventory in YAML:

all:
  children:
    webservers:
      hosts:
        web1.example.com:
        web2.example.com:
        web3.example.com:
    dbservers:
      hosts:
        db1.example.com:
        db2.example.com:
    loadbalancers:
      hosts:
        lb1.example.com:

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Default Groups

Ansible automatically creates two default groups:

Group	Contains
all	Every host in the inventory
ungrouped	Hosts not assigned to any explicit group

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Host Variables

You can assign variables directly to hosts in the inventory:

[webservers]
web1.example.com ansible_port=2222 http_port=8080
web2.example.com ansible_port=22 http_port=80

[dbservers]
db1.example.com ansible_user=dbadmin db_port=5432

Common Connection Variables

Variable	Description	Default
ansible_host	The actual IP or hostname to connect to	The inventory hostname
ansible_port	SSH port	22
ansible_user	SSH user	The control node user
ansible_ssh_private_key_file	Path to the SSH private key	Default SSH key
ansible_become	Enable privilege escalation	false
ansible_python_interpreter	Path to Python on the managed node	Auto-detected

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Group Variables

Assign variables to all hosts in a group:

[webservers]
web1.example.com
web2.example.com

[webservers:vars]
http_port=80
document_root=/var/www/html
ansible_user=deploy

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Nested Groups (Children)

Groups can contain other groups using the :children suffix:

[webservers]
web1.example.com
web2.example.com

[dbservers]
db1.example.com

[production:children]
webservers
dbservers

[production:vars]
env=production

Now targeting production will include all hosts from webservers and dbservers.

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Host and Group Variable Files

For better organisation, store variables in separate files:

inventory/
+-- hosts              # Main inventory file
group_vars/
+-- all.yml            # Variables for all hosts
+-- webservers.yml     # Variables for webservers group
+-- dbservers.yml      # Variables for dbservers group
host_vars/
+-- web1.example.com.yml  # Variables for web1
+-- db1.example.com.yml   # Variables for db1

Example group_vars/webservers.yml

http_port: 80
document_root: /var/www/html
max_clients: 256

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