Lab 002 - 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.

Pre-Requirements¶

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.

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

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

[database]
db1.example.com

YAML format

all:
    hosts:
        web1.example.com:
        web2.example.com:
    children:
        database:
        hosts:
            db1.example.com:

JSON format
```
&qu                   
```
id=__codelineno-2-1 name=__codelineno-2-1 href=#__codelineno-2-1>{ ot;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" ] } } } class=p>}

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.

See an example of generating a dynamic inventory using Python code for fetching data from a database:

```python
#!/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()))
```

04. Lab exercise¶

Let’s create the inventory configuration that we will use for the 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

05. 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'

06. `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
```