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DevOps Day 91: Ansible Lineinfile Module & Web Server Automation

This document outlines the solution for DevOps Day 91. The objective was to create a comprehensive Ansible playbook to deploy an httpd web server, create an initial web page, and then modify that page's content dynamically using the lineinfile module.

Table of Contents

Task Overview

Objective: Install and configure httpd on all app servers, deploy an index.html with initial text, and insert a new welcome message at the top of the file.

Requirements: 1. Playbook: Create /home/thor/ansible/playbook.yml. 2. Web Server: Install httpd, start the service, and enable it on boot. 3. Initial Content: Create /var/www/html/index.html containing "This is a Nautilus sample file, created using Ansible!". 4. Modify Content: Insert "Welcome to xFusionCorp Industries!" at the top of the file using lineinfile. 5. Permissions: File owner/group: apache, Mode: 0644.

Step-by-Step Solution

1. Verify Inventory

First, I verified the inventory file to ensure we could connect to all target servers.

Command: 

cd /home/thor/ansible
ls -l

2. Create the Playbook

I created a multi-task playbook to handle the package installation, service management, file creation, and file modification.

Command: 

vi playbook.yml

Content: 

---
- name: Deploy and Configure Web Server
  hosts: all
  become: yes
  tasks:
    - name: Install httpd package
      yum:
        name: httpd
        state: present

    - name: Start and Enable httpd service
      service:
        name: httpd
        state: started
        enabled: yes

    - name: Create index.html with initial content
      copy:
        dest: /var/www/html/index.html
        content: "This is a Nautilus sample file, created using Ansible!"
        force: yes

    - name: Add welcome message to the top of index.html
      lineinfile:
        path: /var/www/html/index.html
        line: "Welcome to xFusionCorp Industries!"
        insertbefore: BOF
        state: present

    - name: Set ownership and permission for index.html
      file: 
        path: /var/www/html/index.html
        owner: apache
        group: apache
        mode: '0644'

3. Execute and Validate

I ran the playbook against the inventory.

Command: 

ansible-playbook -i inventory playbook.yml

Output Analysis: 

TASK [Add welcome message to the top of index.html] ***************************************************
changed: [stapp01]
changed: [stapp02]
changed: [stapp03]
* Changed: Confirms that Ansible successfully found the file and inserted the new line at the beginning.

Deep Dive: Ansible Concepts Used

The lineinfile Module

This module ensures a particular line is in a file, or replaces an existing line using a regular expression. It's powerful for editing configuration files. * path: The file to modify. * line: The exact line content to insert/ensure exists. * state: present: Ensures the line is added if missing.

The insertbefore Parameter

The task requirement was to add the line at the top of the file. * insertbefore: BOF: This is a special alias. BOF stands for Beginning Of File. It tells Ansible to insert the line before the very first line of the file. * Without this parameter (or using insertafter: EOF), the line would be appended to the end.

Troubleshooting

Issue: "Destination directory does not exist" * Cause: If httpd isn't installed first, /var/www/html won't exist. * Fix: Ensure the yum task runs before any copy or lineinfile tasks.

Issue: Line appended instead of prepended * Cause: Forgetting insertbefore: BOF. * Fix: Add the parameter to the lineinfile task.

Issue: "Permission denied" * Cause: Modifying files in /var/www/html requires root privileges. * Fix: Ensure become: yes is set at the play level.