Ansible Level 03 Day 05: Ansible Replace Module¶

This document outlines the solution for Ansible Level 03 Day 05. The objective was to write an Ansible playbook that modifies the contents of specific text files across multiple application servers. This task highlights the capability of the replace module to perform targeted string substitutions.

Table of Contents¶

Task Overview
Step-by-Step Solution
Deep Dive: Ansible Concepts Used
- The replace Module
- Multiple Plays in One Playbook

Task Overview¶

Objective: Use the Ansible replace module to substitute specific strings in files spread across different app servers.

Requirements: 1. Playbook Location: /home/thor/ansible/playbook.yml on the jump host. 2. App Server 1 (stapp01): In file /opt/devops/blog.txt, replace xFusionCorp with Nautilus. 3. App Server 2 (stapp02): In file /opt/devops/story.txt, replace Nautilus with KodeKloud. 4. App Server 3 (stapp03): In file /opt/devops/media.txt, replace KodeKloud with xFusionCorp Industries. 5. Constraint: Must run successfully using ansible-playbook -i inventory playbook.yml without any extra CLI arguments.

Step-by-Step Solution¶

1. Verify the Environment¶

Since the inventory file is already provided, quickly review it to ensure it contains the required hostnames (stapp01, stapp02, stapp03) and their respective connection variables.

Command:

cd /home/thor/ansible
cat inventory

2. Create the Playbook¶

Create a YAML playbook structured with three distinct plays. This approach cleanly targets each server individually and applies the corresponding file path and string replacement logic required for that specific server. Modifying files under /opt requires elevated privileges, so become: yes must be included.

Command:

vi playbook.yml

Content:

---
- name: Update data on App Server 1
  hosts: stapp01
  become: yes
  tasks:
    - name: Replace xFusionCorp with Nautilus in blog.txt
      replace:
        path: /opt/devops/blog.txt
        regexp: 'xFusionCorp'
        replace: 'Nautilus'

- name: Update data on App Server 2
  hosts: stapp02
  become: yes
  tasks:
    - name: Replace Nautilus with KodeKloud in story.txt
      replace:
        path: /opt/devops/story.txt
        regexp: 'Nautilus'
        replace: 'KodeKloud'

- name: Update data on App Server 3
  hosts: stapp03
  become: yes
  tasks:
    - name: Replace KodeKloud with xFusionCorp Industries in media.txt
      replace:
        path: /opt/devops/media.txt
        regexp: 'KodeKloud'
        replace: 'xFusionCorp Industries'

3. Execute and Validate¶

Run the playbook from the /home/thor/ansible/ directory.

Execution Command:

ansible-playbook -i inventory playbook.yml

Expected Output:

PLAY [Update data on App Server 1] **************************************************
...
changed: [stapp01]

PLAY [Update data on App Server 2] **************************************************
...
changed: [stapp02]

PLAY [Update data on App Server 3] **************************************************
...
changed: [stapp03]

PLAY RECAP **************************************************************************
stapp01                    : ok=2    changed=1    unreachable=0    failed=0    ...
stapp02                    : ok=2    changed=1    unreachable=0    failed=0    ...
stapp03                    : ok=2    changed=1    unreachable=0    failed=0    ...

Manual Verification (Optional): To verify the content of the files on the remote servers, use ad-hoc commands:

ansible stapp01 -i inventory -m command -a "cat /opt/devops/blog.txt" --become
ansible stapp02 -i inventory -m command -a "cat /opt/devops/story.txt" --become
ansible stapp03 -i inventory -m command -a "cat /opt/devops/media.txt" --become

Deep Dive: Ansible Concepts Used¶

The `replace` Module¶

The replace module is designed to replace all instances of a particular string in a file based on a regular expression. * path: The absolute path to the file on the remote machine that needs to be modified. * regexp: The regular expression (or string, as used in this scenario) to look for in every line of the file. * replace: The string to substitute into the file wherever the regexp matches. * Idempotency: If the string specified in regexp is no longer found in the file (e.g., because the playbook was already run), Ansible will correctly report ok instead of changed, ensuring no unintended side effects.

Multiple Plays in One Playbook¶

Instead of using conditionals (when) under a single hosts: all declaration, defining multiple discrete plays (one for each hosts: stapp0X) is often cleaner when entirely different actions, paths, and values apply to entirely different servers. This keeps the YAML easily readable and self-documenting.