Tech Tutorial: Understand Core Components of Ansible - Loops #

Exam Objective: Loops

Introduction #

In this tutorial, we will delve into an essential aspect of Ansible, one of the most popular automation tools used in systems administration and DevOps - Loops. Specifically designed for the Red Hat Certified Engineer (RHCE) exam, this guide will focus entirely on practical, real-world examples using Red Hat Enterprise Linux (RHEL) as the primary operating system.

Loops in Ansible are powerful constructs that allow you to repeat a particular task multiple times. This can be beneficial when you need to manage a series of resources similarly or apply a configuration across multiple items.

Step-by-Step Guide #

1. Setting Up Your Environment #

Before diving into the Ansible loops, ensure you have an Ansible control node and one or more managed nodes running RHEL. Here’s a quick setup:

• Control Node: A RHEL system with Ansible installed.
• Managed Nodes: One or more RHEL systems that you will manage with Ansible.

Install Ansible on the control node using the following command:

sudo dnf install ansible

Ensure SSH access from the control node to the managed nodes for seamless automation.

2. Understanding Basic Loop Structure #

The simplest form of a loop in Ansible uses the loop keyword. Let’s start with a basic example:

Example: Create Multiple Users #

Create a new playbook named create_users.yml.

---
- name: Create multiple users
  hosts: all
  tasks:
    - name: Ensure users are present
      user:
        name: "{{ item }}"
        state: present
      loop:
        - alice
        - bob
        - carol

This playbook loops over the list provided under the loop keyword and creates users on the target machines.

3. Advanced Loop Examples #

Using with_items #

This is another way to implement loops, which is very similar to loop but specific to certain modules.

---
- name: Install multiple packages
  hosts: all
  tasks:
    - name: Ensure packages are installed
      yum:
        name: "{{ item }}"
        state: present
      with_items:
        - httpd
        - vim
        - tree

This playbook installs multiple packages on RHEL systems using the yum module.

Looping Over Hashes/Dictionaries #

When you need to loop over a dictionary, you can use the dict2items filter.

---
- name: Add several users with attributes
  hosts: all
  vars:
    users:
      alice:
        uid: 1001
        shell: /bin/bash
      bob:
        uid: 1002
        shell: /bin/zsh
  tasks:
    - name: Ensure users with attributes are present
      user:
        name: "{{ item.key }}"
        uid: "{{ item.value.uid }}"
        shell: "{{ item.value.shell }}"
        state: present
      loop: "{{ lookup('dict', users).items() }}"

This playbook creates users with specific uid and shell attributes, demonstrating how to handle more complex data structures.

4. Error Handling in Loops #

You can manage errors within loops using the ignore_errors directive or by handling failures more gracefully with rescue blocks in blocks.

---
- name: Attempt to execute potentially failing commands
  hosts: all
  tasks:
    - block:
        - command: "{{ item }}"
          loop:
            - 'echo "This will succeed"'
            - 'exit 1'  # This command will fail
      rescue:
        - debug:
            msg: "A command failed, but we're moving on!"

Conclusion #

In this tutorial, we explored the essential aspects of using loops in Ansible, focusing on practical examples tailored for RHEL as required for the RHCE exam. Mastery of loops enhances your ability to write more dynamic and efficient playbooks, significantly reducing code redundancy and making your automation tasks more manageable and scalable. As you prepare for the exam, practice these examples and experiment with variations to deepen your understanding of Ansible’s capabilities.