Tech Tutorial: Create Ansible Plays and Playbooks Using Variables to Retrieve the Results of Running a Command #

Introduction #

Ansible is a powerful automation tool that simplifies configuration management, application deployment, and many other administrative tasks. In this tutorial, we will focus on a specific aspect of Ansible relevant to the Red Hat Certified Engineer (RHCE) exam: using variables to retrieve the results of running a command. This capability is crucial for creating dynamic and responsive playbooks that adapt based on the state of the system or the output of prior tasks.

Step-by-Step Guide #

Prerequisites #

A Red Hat Enterprise Linux (RHEL) system (version 8 or later recommended).
Ansible installed on your control node (the system from which you will run Ansible commands).
SSH access configured for a target node (another RHEL system) where commands will be executed.

Setting Up Your Environment #

Install Ansible on RHEL: If Ansible is not already installed on your RHEL system, you can install it using the following command:
```
sudo dnf install ansible -y
```
Configure SSH Access: Ensure you have SSH access set up for the user that will run Ansible on your control node to your target node. This usually involves setting up SSH keys and ensuring the public key is in the ~/.ssh/authorized_keys file on the target node.
Test Ansible Connectivity:
Create an inventory file named hosts:
```
[servers]
server1 ansible_host=target_node_ip ansible_user=remote_user
```
Replace target_node_ip with the IP address of your target node and remote_user with the user that will run Ansible commands.
Test the connection using:
```
ansible all -i hosts -m ping
```

Creating the Playbook #

Now, let’s create a playbook that runs a command on the target node and uses a variable to store the result.

Create the Playbook File:

Create a file named check_disk.yml:

---
- name: Check disk space on a target node
  hosts: servers
  tasks:
    - name: Get disk space usage
      command: df -h /home
      register: disk_space

    - name: Print disk space usage
      debug:
        msg: "Disk space on /home: {{ disk_space.stdout }}"

In this playbook:

The command module runs df -h /home on the target node to check the disk space usage of the /home directory.
The register keyword saves the output of the command to the disk_space variable.
The debug module prints the output stored in disk_space.stdout.

Running the Playbook #

Execute the playbook using the following command:

ansible-playbook -i hosts check_disk.yml

This command runs your playbook using the inventory file hosts which specifies the target node details.

Detailed Code Examples #

Let’s dive deeper into some variations and real-world scenarios where capturing command output can be crucial.

Checking Service Status #

Suppose you want to check the status of a service and perform an action based on its status. Here’s how you can do it:

---
- name: Check and report service status
  hosts: servers
  tasks:
    - name: Check status of crond service
      command: systemctl status crond
      register: service_status
      ignore_errors: yes

    - name: Print service status
      debug:
        msg: "Service status: {{ service_status.stdout }}"

Conclusion #

Using variables to capture the output of commands in Ansible allows you to make decisions and perform actions based on the state of your systems dynamically. This approach is integral to writing flexible and efficient automation scripts, particularly in complex IT environments like those managed under RHCE standards. By mastering this skill, you enhance your ability to manage Red Hat systems effectively and prepare yourself for scenarios you may encounter in the RHCE exam and real-world tasks.

Keep experimenting with different modules and exploring Ansible’s extensive documentation to further your understanding and expertise.