No Inventory¶

In this lab we will learn about Ansible inventory and how it affects automation tasks.
We will start with an empty inventory and observe Ansible’s behavior with no hosts defined. Later, we will create and test the inventory file.
This lab is based upon the previous lab and its docker-compose setup.

What will we learn?¶

How Ansible behaves with no inventory defined
How to create and configure an inventory file in various formats (INI, YAML, JSON)
How to use inventory variables and groups
The difference between static and dynamic inventory

Prerequisites¶

Complete the previous lab in order to have Ansible configured.

01. “Clear” the inventory¶

Let’s clear the inventory from previous labs and walk through what is inventory.
Create an empty inventory file or remove all host entries from existing inventory:

# Option 1: Create empty inventory file
touch $RUNTIME_FOLDER/labs-scripts/inventory

# Option 2: Clear existing inventory
echo "# Empty inventory" > $RUNTIME_FOLDER/labs-scripts/inventory

02. Create the `inventory` file¶

Ansible Inventory¶

An Ansible inventory can either be a single file or a collection of files
The inventory defines the [hosts] and [groups] of hosts upon which Ansible will operate.
It’s simply a list of servers that Ansible can connect with and manage.

Key features of Ansible inventory¶

Can be in various formats, such as INI, JSON, YAML and more.
YAML being the most common format.
inventory defines the target hosts for playbook execution.
inventory organizes hosts into logical groups for easier management.
inventory can store host-specific variables and group variables.
inventory supports nested groups (groups of groups).

03. `inventory` samples¶

INI format (basic)¶

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

[database]
db1.example.com

INI format with variables¶

[webservers]
web1.example.com ansible_port=2222 ansible_user=admin
web2.example.com ansible_port=2223 ansible_user=admin

[webservers:vars]
http_port=80
max_connections=100

[database]
db1.example.com ansible_port=5432

[database:vars]
db_type=postgresql

YAML format¶

all:
  children:
    webservers:
      hosts:
        web1.example.com:
          ansible_port: 2222
          ansible_user: admin
        web2.example.com:
          ansible_port: 2223
          ansible_user: admin
      vars:
        http_port: 80
        max_connections: 100
    database:
      hosts:
        db1.example.com:
          ansible_port: 5432
      vars:
        db_type: postgresql

JSON format

{
  "all": {
    "hosts": {
      "web1.example.com": {
        "ansible_port": 2222,
        "http_port": 80
      },
      "web2.example.com": {
        "ansible_port": 2223,
        "http_port": 8080
      }
    },
    "children": {
      "database": {
        "hosts": ["db1.example.com"]
      }
    }
  }
}

04. Special Groups in Ansible¶

all - Contains every host in the inventory (automatically created)
ungrouped - Contains hosts not assigned to any group (automatically created)

# Hosts in 'all' group but not in any specific group
standalone-server.example.com

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

05. Inventory Variables¶

Ansible allows you to define variables at different levels:

Host Variables¶

Variables specific to individual hosts:

[webservers]
web1.example.com ansible_port=2222 environment=production
web2.example.com ansible_port=2223 environment=staging

Group Variables¶

Variables shared by all hosts in a group:

[webservers:vars]
ansible_user=admin
http_port=80

Common Ansible Variables¶

Variable	Description	Example
`ansible_host`	Target IP address or hostname	`192.168.1.10`
`ansible_port`	SSH port	`2222`
`ansible_user`	SSH username	`admin`
`ansible_ssh_private_key_file`	SSH key path	`/path/to/key`
`ansible_connection`	Connection type	`ssh`, `local`
`ansible_python_interpreter`	Python path on target	`/usr/bin/python3`

06. Inventory types in Ansible¶

Static Inventory
This is generally a simple text file (usually in INI or YAML format) that lists the hosts and their corresponding groups.
Dynamic Inventory

This is generated by a script or a program that retrieves host information from an external source (such as cloud providers like AWS, Azure, etc.), LDAP or from a database.

This allows for real-time updates and adaptability as environments change.

Simple Dynamic Inventory Example¶

A basic Python script that generates inventory:

#!/usr/bin/env python3
import json

def get_inventory():
    inventory = {
        'webservers': {
            'hosts': ['web1.example.com', 'web2.example.com'],
            'vars': {'http_port': 80}
        },
        'database': {
            'hosts': ['db1.example.com'],
            'vars': {'db_port': 5432}
        }
    }
    return inventory

if __name__ == "__main__":
    print(json.dumps(get_inventory()))

Advanced Dynamic Inventory with Database¶

Example of generating a dynamic inventory using Python code for fetching data from a database:

#!/usr/bin/env python
import sqlite3
import json

def get_inventory():
    conn = sqlite3.connect('servers.db')
    cursor = conn.cursor()

    cursor.execute('SELECT hostname, group_name, ansible_user FROM servers')
    rows = cursor.fetchall()

    inventory = {'all': {'hosts': [], 'vars': {}}}

    for row in rows:
        hostname, group_name, ansible_user = row

        if group_name not in inventory:
            inventory[group_name] = {'hosts': [], 'vars': {}}

        inventory['all']['hosts'].append(hostname)
        inventory[group_name]['hosts'].append(hostname)
        inventory[group_name]['vars']['ansible_user'] = ansible_user

    conn.close()
    return inventory

if __name__ == "__main__":
    print(json.dumps(get_inventory()))

07. Best Practices for Inventory Management¶

Organization
Use descriptive group names that reflect server roles
Create parent-child group relationships for complex infrastructures
Keep inventory files in version control
Variables
Store sensitive data in Ansible Vault, not plain text inventory
Use group_vars/ and host_vars/ directories for complex variable structures
Keep inventory-specific variables in inventory, playbook-specific ones in playbooks
Scalability
Use dynamic inventory for cloud environments
Organize large inventories into multiple files
Use inventory plugins for modern Ansible versions
Example: Nested Groups¶

[web_prod]
web-prod-1.example.com
web-prod-2.example.com

[web_staging]
web-staging-1.example.com

[webservers:children]
web_prod
web_staging

[production:children]
web_prod
db_prod

08. Lab exercise¶

Let’s create the inventory configuration that we will use for the rest of our labs:

### File location: $RUNTIME_FOLDER/labs-scripts/inventory
###
### List of servers which we want Ansible to connect to
### The names are defined in the docker-compose
###

[servers]
# No server will be defined at this step

09. No inventory invocation¶

Once all is ready, let’s check if the controller can connect to the servers using ping

# Ping the servers and check that they are "alive"
docker exec ansible-controller sh -c "cd /labs-scripts && ansible all -m ping"

## Output
## -------------------------------------------------------------------------------
[WARNING]: provided hosts list is empty, only localhost is available. Note that
the implicit localhost does not match 'all'

10. `inventory` invocation¶

Fill in the inventory based upon the previous labs’ configuration and test it.
Verify that the inventory is defined correctly with:
```
ansible-inventory -i <inventory_file> --graph
```
Test the inventory file with
```
ansible -i <inventory_file> -m ping
```

11. More Hands-on Exercises¶

Create an inventory file with two groups: webservers and databases, with at least 2 hosts each.

??? success “Solution” ```ini [webservers] web1.example.com web2.example.com

  [databases]
  db1.example.com
  db2.example.com
  ```

Add host variables to set different SSH ports for each host in your inventory.

??? success “Solution” ```ini [webservers] web1.example.com ansible_port=2222 web2.example.com ansible_port=2223

  [databases]
  db1.example.com ansible_port=2224
  db2.example.com ansible_port=2225
  ```

Create an inventory with group variables that set ansible_user=admin for all webservers.

??? success “Solution” ```ini [webservers] web1.example.com web2.example.com

  [webservers:vars]
  ansible_user=admin
  ```

Create a nested group structure where production contains both web_prod and db_prod groups.

??? success “Solution” ```ini [web_prod] web-prod-1.example.com web-prod-2.example.com

  [db_prod]
  db-prod-1.example.com

  [production:children]
  web_prod
  db_prod
  ```

Use ansible-inventory command to list all hosts in a specific group.

??? success “Solution” ```sh # List all hosts in webservers group ansible-inventory -i inventory –list –limit webservers

  # Show graph view
  ansible-inventory -i inventory --graph webservers
  ```

Create a YAML format inventory with the same structure as your INI inventory.

??? success “Solution” yaml all: children: webservers: hosts: web1.example.com: ansible_port: 2222 web2.example.com: ansible_port: 2223 vars: ansible_user: admin databases: hosts: db1.example.com: ansible_port: 5432

Test your inventory by pinging only hosts in the webservers group.

??? success “Solution” sh ansible webservers -i inventory -m ping

12. Summary¶

Inventory is the foundation of Ansible automation - it defines what hosts to manage
Supports multiple formats: INI, YAML, and JSON
Can be static (text files) or dynamic (generated by scripts)
Use groups to organize hosts logically by role, environment, or location
Variables can be set at host or group level for flexibility
Special groups all and ungrouped are automatically created
Use ansible-inventory command to validate and inspect inventory
Follow best practices: version control, nested groups, and Ansible Vault for secrets
Dynamic inventory is essential for cloud and large-scale environments

No Inventory¶

What will we learn?¶

Prerequisites¶

01. “Clear” the inventory¶

02. Create the `inventory` file¶

Ansible Inventory¶

Key features of Ansible inventory¶

03. `inventory` samples¶

`INI` format (basic)¶

`INI` format with variables¶

`YAML` format¶

04. Special Groups in Ansible¶

05. Inventory Variables¶

Host Variables¶

Group Variables¶

Common Ansible Variables¶

06. Inventory types in Ansible¶

Simple Dynamic Inventory Example¶

Advanced Dynamic Inventory with Database¶

07. Best Practices for Inventory Management¶

Example: Nested Groups¶

08. Lab exercise¶

09. No inventory invocation¶

10. `inventory` invocation¶

11. More Hands-on Exercises¶

12. Summary¶

No Inventory¶

What will we learn?¶

Prerequisites¶

01. “Clear” the inventory¶

02. Create the inventory file¶

Ansible Inventory¶

Key features of Ansible inventory¶

03. inventory samples¶

INI format (basic)¶

INI format with variables¶

YAML format¶

04. Special Groups in Ansible¶

05. Inventory Variables¶

Host Variables¶

Group Variables¶

Common Ansible Variables¶

06. Inventory types in Ansible¶

Simple Dynamic Inventory Example¶

Advanced Dynamic Inventory with Database¶

07. Best Practices for Inventory Management¶

Example: Nested Groups¶

08. Lab exercise¶

09. No inventory invocation¶

10. inventory invocation¶

11. More Hands-on Exercises¶

12. Summary¶

02. Create the `inventory` file¶

03. `inventory` samples¶

`INI` format (basic)¶

`INI` format with variables¶

`YAML` format¶

10. `inventory` invocation¶