Tech Tutorial: Understand Core Components of Ansible - Inventories #

Introduction #

In the world of automation and configuration management, Ansible stands out due to its simplicity and ease of use. For Red Hat Certified Engineer (RHCE) exam takers, understanding how Ansible works, particularly its inventory, is crucial. An inventory is essentially a list of nodes or hosts that Ansible manages. It can be defined in a static file (usually a simple text format) or dynamically generated.

This tutorial covers the concept of inventories in Ansible, focusing on the Red Hat Enterprise Linux (RHEL) distribution. We will explore how to define and organize hosts, group them, and specify variables within inventories using practical and real-world examples.

Step-by-Step Guide #

1. Setting up Ansible on RHEL #

Before diving into inventories, ensure that Ansible is installed on your RHEL system. You can install Ansible using the following YUM command:

sudo yum install ansible

2. Understanding the Inventory File #

By default, Ansible looks for the inventory file at /etc/ansible/hosts. However, you can specify a custom inventory file using the -i option with the ansible commands.

An inventory file can be as simple as:

# /etc/ansible/hosts
192.168.1.50
192.168.1.51

This file lists two managed nodes by their IP addresses.

3. Grouping Hosts #

Organizing hosts into groups can simplify managing multiple servers. Here’s an example of an inventory file with grouped hosts:

# /etc/ansible/hosts
[webservers]
webserver1.example.com
webserver2.example.com

[dbservers]
dbserver1.example.com
dbserver2.example.com

In this example, webserver1.example.com and webserver2.example.com are grouped under [webservers], and dbserver1.example.com and dbserver2.example.com are grouped under [dbservers].

4. Nested Groups #

Ansible also supports nested groups:

# /etc/ansible/hosts
[webservers]
webserver1.example.com
webserver2.example.com

[dbservers]
dbserver1.example.com
dbserver2.example.com

[linux:children]
webservers
dbservers

Here, [linux:children] is a supergroup that includes both [webservers] and [dbservers].

5. Host Variables #

You can define variables specific to a host directly in the inventory file:

# /etc/ansible/hosts
[webservers]
webserver1.example.com http_port=80 max_requests=200
webserver2.example.com http_port=8080 max_requests=100

6. Group Variables #

Similar to host variables, you can define variables for a whole group:

# /etc/ansible/hosts
[webservers:vars]
http_port=80
max_requests=200

This sets http_port and max_requests for all hosts under the [webservers] group.

Detailed Code Examples #

Let’s run a simple command to check the connectivity of all the servers under the webservers group:

ansible webservers -m ping

This command uses the ping module to ensure that all hosts in the webservers group are reachable.

Conclusion #

Understanding and effectively managing inventories is a foundational skill for using Ansible, especially for system administrators aiming for the RHCE certification. The ability to group hosts and define relevant variables allows for scalable and flexible configurations. By mastering inventories, you can streamline the management of numerous systems in a RHEL environment, making your automation tasks more organized and efficient.