Ansible Tower Inventories

Introduction

When managing infrastructure with Ansible, one of the first and most important components you'll work with is inventories. In Ansible Tower (or its open-source counterpart AWX), inventories are central to organizing and targeting your automation. An inventory is essentially a collection of hosts and groups that Ansible can manage, along with their variables and connection details.

Think of an inventory as your "address book" for automation - it tells Ansible Tower which systems it can reach, how to reach them, and provides additional information about those systems that can be used during playbook execution.

Understanding Inventory Basics

What Are Inventories in Ansible Tower?

Inventories in Ansible Tower extend the concept of basic Ansible inventories with additional features:

• Web-based management: Create and edit inventories through a user-friendly interface
• Role-based access control: Control who can view or modify inventory information
• Dynamic inventories: Automatically populate hosts from external sources
• Real-time status: See which hosts are available and their latest facts
• Multi-credential support: Use different authentication methods for different hosts

Types of Inventories

Ansible Tower supports two main types of inventories:

1. Static Inventories: Manually defined lists of hosts and groups
2. Dynamic Inventories: Automatically generated from external sources like cloud providers, virtualization platforms, or CMDBs

Creating and Managing Inventories

Creating a Static Inventory

Let's start by creating a basic static inventory in Ansible Tower:

1. Navigate to Inventories in the Ansible Tower dashboard
2. Click the Add button and select Add inventory
3. Fill in the required fields:
   • Name: A descriptive name (e.g., "Production Servers")
   • Organization: Your organization in Ansible Tower
   • Description: Optional information about the inventory

Adding Hosts to an Inventory

Once you've created an inventory, you can add hosts:

1. From your inventory, click the Hosts button
2. Click Add
3. Enter the hostname or IP address
4. Add any variables specific to this host
5. Click Save

Example host variables in YAML format:

yaml

ansible_host: 192.168.1.100
ansible_user: admin
ansible_connection: ssh
ansible_ssh_private_key_file: /path/to/key
environment: production
role: web_server

Creating Host Groups

Groups help organize hosts by function, location, or other criteria:

1. From your inventory, click the Groups button
2. Click Add
3. Enter a name and description
4. Click Save
5. Select the group and click Hosts
6. Add hosts to the group

Groups can also contain other groups, allowing for hierarchical organization:

yaml

all:
  children:
    datacenter_east:
      children:
        web_servers:
          hosts:
            web01.example.com:
            web02.example.com:
        database_servers:
          hosts:
            db01.example.com:
            db02.example.com:
    datacenter_west:
      children:
        web_servers:
          hosts:
            web03.example.com:
            web04.example.com:

Using Variables with Inventories

Ansible Tower inventories support variables at multiple levels:

Host Variables

Variables specific to individual hosts:

1. Navigate to a host within your inventory
2. Click on the Variables tab
3. Enter variables in YAML or JSON format:

yaml

ansible_port: 2222
memory_size: 8GB
application_version: 1.5.2
backup_enabled: true

Group Variables

Variables applied to all hosts in a group:

1. Navigate to a group within your inventory
2. Click on the Variables tab
3. Enter variables in YAML or JSON format:

yaml

ntp_server: ntp.example.com
dns_servers:
  - 8.8.8.8
  - 8.8.4.4
security_updates: daily
monitoring_enabled: true

Inventory Variables

Variables applied to the entire inventory:

1. Navigate to your inventory
2. Click on the Variables tab
3. Enter variables in YAML or JSON format:

yaml

ansible_become: true
ansible_become_method: sudo
company_name: "Acme Inc."
default_timezone: "UTC"

Working with Dynamic Inventories

Dynamic inventories automatically fetch host information from external sources.

Setting Up a Dynamic Inventory

1. Navigate to Inventories and click Add
2. Select Add inventory source
3. Fill in the required fields:
   • Name: A descriptive name (e.g., "AWS EC2 Instances")
   • Source: Select your inventory source (AWS, GCP, VMware, etc.)
   • Credential: Select the appropriate credential for the source
   • Update Options: Configure how often to sync

Example: AWS EC2 Dynamic Inventory

Here's how to set up a dynamic inventory for AWS EC2 instances:

1. Create an AWS credential in Ansible Tower
2. Create a new inventory
3. Add an inventory source with the following settings:
   • Source: Amazon EC2
   • Credential: Your AWS credential
   • Regions: Select AWS regions to include
   • Instance Filters: Optional filters (e.g., tag:Environment=Production)
   • Update Options: Enable "Update on Launch"

When this inventory syncs, it will automatically:

• Create groups based on AWS attributes (regions, availability zones, security groups, tags)
• Import all instance details as host variables
• Update when instances are created or terminated

Practical Examples

Example 1: Multi-Environment Web Application Deployment

Let's create an inventory structure for a web application with multiple environments:

yaml

# Inventory Variables
---
ansible_become: true
default_ssh_user: deployer

# Group: All Environments
all:
  children:
    development:
      vars:
        environment: dev
        debug_mode: true
      hosts:
        dev-web01:
          ansible_host: 192.168.10.101
        dev-web02:
          ansible_host: 192.168.10.102
        dev-db01:
          ansible_host: 192.168.10.201
          db_role: primary
    
    staging:
      vars:
        environment: stage
        debug_mode: false
      hosts:
        stage-web01:
          ansible_host: 192.168.20.101
        stage-web02:
          ansible_host: 192.168.20.102
        stage-db01:
          ansible_host: 192.168.20.201
          db_role: primary
    
    production:
      vars:
        environment: prod
        debug_mode: false
        backup_retention: 30
      hosts:
        prod-web01:
          ansible_host: 192.168.30.101
        prod-web02:
          ansible_host: 192.168.30.102
        prod-web03:
          ansible_host: 192.168.30.103
        prod-db01:
          ansible_host: 192.168.30.201
          db_role: primary
        prod-db02:
          ansible_host: 192.168.30.202
          db_role: replica

This structure allows you to:

• Target specific environments (e.g., development, staging, production)
• Apply environment-specific variables
• Run playbooks against all web servers or database servers across environments

Example 2: Using Inventory to Target Specific Hosts

When running a job template in Ansible Tower, you can use the inventory structure to target specific hosts or groups:

yaml

# Playbook: update_web_servers.yml
---
- name: Update Web Servers
  hosts: development:staging  # Target both development and staging environments
  tasks:
    - name: Update packages
      apt:
        update_cache: yes
        upgrade: yes
      become: yes
      
    - name: Restart web service
      service:
        name: nginx
        state: restarted
      become: yes

Example 3: Using Inventory Variables in Templates

You can use inventory variables in your templates to customize configurations:

yaml

# Template: nginx.conf.j2
server {
    listen 80;
    server_name {{ inventory_hostname }};
    
    {% if environment == 'dev' %}
    # Development-specific settings
    error_log /var/log/nginx/error.log debug;
    {% elif environment == 'prod' %}
    # Production-specific settings
    error_log /var/log/nginx/error.log warn;
    {% endif %}
    
    location / {
        root /var/www/{{ application_name }};
        index index.html;
    }
}

Best Practices for Ansible Tower Inventories

1. Use a Consistent Naming Convention

Adopt a consistent naming scheme for hosts and groups:

• Use descriptive names that indicate function and environment
• Consider including location or datacenter information
• Be consistent with case and separators

2. Implement a Logical Group Hierarchy

Create a sensible hierarchy that reflects your infrastructure:

• Group by environment (dev, test, prod)
• Group by function (web, database, cache)
• Group by location (east, west, europe)
• Use nested groups to represent relationships

3. Leverage Variables Effectively

Use variables at the appropriate level:

• Host variables for host-specific settings
• Group variables for shared settings
• Inventory variables for global settings

4. Keep Credentials Separate

Don't store sensitive data in your inventory:

• Use Ansible Tower's credential system instead
• Leverage lookups or Ansible Vault for sensitive variables
• Use different credentials for different environments

5. Set Up Regular Syncs for Dynamic Inventories

Keep your dynamic inventories up to date:

• Schedule regular syncs
• Enable "Update on Launch" for job templates
• Monitor sync failures

6. Document Your Inventory Structure

Maintain documentation about your inventory:

• Add descriptions to inventories, groups, and hosts
• Use comments in variable files
• Document the purpose of custom variables

Troubleshooting Inventory Issues

Common Problems and Solutions

1. Hosts Not Showing Up in Dynamic Inventory

   • Check credential permissions
   • Verify API access to the source
   • Review filters that might be excluding hosts

2. Cannot Connect to Hosts

   • Verify network connectivity
   • Check SSH key or password credentials
   • Ensure correct ansible_host variable is set
   • Verify firewall rules allow connections

3. Variable Precedence Issues

   • Remember Ansible's variable precedence order:
     • Host variables override group variables
     • Child group variables override parent group variables
   • Use ansible-inventory --list to verify the final variable values

Summary

Ansible Tower inventories are a powerful way to organize and manage your infrastructure for automation. By properly structuring your inventories, you can:

• Keep your infrastructure organized and documented
• Target specific groups of hosts for different tasks
• Apply variables at the appropriate levels
• Automatically sync with external sources
• Control access to sensitive infrastructure information

Mastering inventories is a fundamental skill for effectively using Ansible Tower/AWX and is essential for scaling your automation efforts across large or complex environments.

Additional Resources

• Ansible Tower Documentation
• Ansible Inventory Guide
• Ansible AWX Project

Exercises

1. Create a static inventory for a three-tier application with web, application, and database servers in development and production environments.

2. Set up a dynamic inventory source for your preferred cloud provider and organize the imported hosts into custom groups.

3. Create a playbook that targets specific host groups in your inventory and uses inventory variables to customize the configuration.

4. Build an inventory structure that models a multi-datacenter infrastructure with redundant services in each location.

5. Experiment with inventory plugins to automatically generate inventory from external sources like CSV files or custom APIs.