Ansible Inventory

Ansible Inventory

Activate when defining which hosts Ansible should manage, grouping hosts, setting connection parameters, or configuring dynamic inventory sources like AWS or Azure.

Anti-fabrication

This skill follows core:anti-fabrication. The claim area is references/dynamic- inventory.md's three dynamic-inventory plugin option tables — aws_ec2, azure_rm, gcp_compute — plus the --limit pattern syntax and connection-vars table, all independently verified against live-installed collections (claude-skills-223): aws_ec2/constructed against ansible-core 2.21.2; azure_rm against azure.azcollection 3.21.0 via ansible-doc -t inventory azure.azcollection.azure_rm (3 corrections — exclude_vm_resource_groups does not exist, hostnames: [default] hashes the name rather than using it plain, auth_source: auto's precedence comment omitted a step); gcp_compute against google.cloud 1.14.0 via ansible-doc -t inventory google.cloud.gcp_compute plus its source (1 correction — auth_kind is required with no default). One item stays explicitly unverified: whether GCP's aggregatedList filter needs quoted string label values — no live GCP project was available to test. Re-verify against a current ansible-doc -t inventory for the plugin in question before asserting an option this skill doesn't cover.

What Is Inventory

An inventory maps the control node's knowledge of managed nodes. At minimum it lists hostnames or IP addresses. Inventory also defines groups, per-host and per-group variables, and connection parameters.

Ansible looks for inventory in this order:

1. -i flag on the command line
2. inventory key in ansible.cfg
3. /etc/ansible/hosts (fallback default)

# ansible.cfg
[defaults]
inventory = inventory/

Static Inventory — INI Format

# inventory/hosts.ini

# Ungrouped hosts
192.168.1.10
backup.example.com

[webservers]
web1.example.com
web2.example.com ansible_port=2222    # host-level variable inline

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

[webservers:vars]
http_port=80
max_connections=200

[production:children]   # group of groups
webservers
dbservers

Static Inventory — YAML Format

# inventory/hosts.yml
all:
  children:
    webservers:
      hosts:
        web1.example.com:
          ansible_port: 22
        web2.example.com:
      vars:
        http_port: 80
    dbservers:
      hosts:
        db1.example.com:
        db2.example.com:
    production:
      children:
        webservers:
        dbservers:
  vars:
    ansible_user: deploy          # applies to all hosts

Host Patterns

Use patterns with -i or in the hosts: field to target a subset:

# In ansible-playbook command
ansible-playbook site.yml --limit webservers
ansible-playbook site.yml --limit "web1.example.com,web2.example.com"

# Wildcard
ansible-playbook site.yml --limit "web*.example.com"

# Union (comma separated)
ansible-playbook site.yml --limit "webservers,dbservers"

# Intersection (AND): hosts in both groups
ansible-playbook site.yml --limit "production:&webservers"

# Exclusion (NOT): production but not dbservers
ansible-playbook site.yml --limit "production:!dbservers"

# Numeric ranges
ansible-playbook site.yml --limit "web[1:5].example.com"

In a playbook hosts: field:

- hosts: webservers:&production   # webservers that are also in production
- hosts: all:!dbservers           # every host except dbservers

group_vars and host_vars

Variables in these directories are automatically loaded by Ansible — no explicit include needed.

inventory/
├── hosts.ini
├── group_vars/
│   ├── all.yml           # applies to every host in every group
│   ├── webservers.yml    # applies to webservers group
│   └── webservers/       # directory form: all files here merge together
│       ├── main.yml
│       └── vault.yml     # encrypted vars (ansible-vault)
└── host_vars/
    ├── web1.example.com.yml    # applies to this specific host
    └── db1.example.com/
        ├── main.yml
        └── vault.yml

# group_vars/webservers.yml
nginx_version: "1.24"
app_root: /var/www/html

Connection Variables

Set these per host or group to control how Ansible connects:

# host_vars/web1.example.com.yml
ansible_host: 10.0.1.15
ansible_user: ubuntu
ansible_ssh_private_key_file: ~/.ssh/deploy_key
ansible_become: true

Dynamic Inventory

When infrastructure changes frequently (cloud, containers), use a dynamic inventory plugin instead of a static file. Plugins query your cloud provider's API and return hosts at runtime.

Using a Plugin

Create a YAML file that ends in .yml or .yaml and configure the plugin:

# inventory/aws_ec2.yml
plugin: amazon.aws.aws_ec2
regions:
  - us-east-1
  - us-west-2
filters:
  instance-state-name: running
  tag:Environment: production
keyed_groups:
  - key: tags.Role
    prefix: role
  - key: placement.region
    prefix: region
hostnames:
  - private-ip-address

# inventory/azure_rm.yml
plugin: azure.azcollection.azure_rm
auth_source: auto
include_vm_resource_groups:
  - my-resource-group
keyed_groups:
  - key: tags.Environment
    prefix: env

Install the collection before use:

ansible-galaxy collection install amazon.aws
ansible-galaxy collection install azure.azcollection

Inspecting Inventory

Always verify your inventory before running a playbook:

ansible-inventory -i inventory/ --list          # JSON dump of all hosts and vars
ansible-inventory -i inventory/ --graph         # tree view of groups
ansible-inventory -i inventory/ --host web1     # vars for a specific host
ansible all -m ping                             # test connectivity to all hosts
ansible webservers -m ping -i inventory/        # test a group

References

• dynamic-inventory.md — AWS EC2, Azure, GCP inventory plugin config examples; constructing groups from instance tags