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DevOps Day 93: Using Ansible Conditionals

This document outlines the solution for DevOps Day 93. The objective was to create a single Ansible playbook that runs on all hosts but performs different file copy operations depending on the specific server node name using the when conditional statement.

Table of Contents

Task Overview

Objective: Distribute specific files to specific App Servers using a single playbook targeting all hosts.

Requirements: 1. Playbook: Create /home/thor/ansible/playbook.yml. 2. Target: hosts: all. 3. Logic: * If node is stapp01: Copy blog.txt to /opt/devops/. Owner: tony. * If node is stapp02: Copy story.txt to /opt/devops/. Owner: steve. * If node is stapp03: Copy media.txt to /opt/devops/. Owner: banner. 4. Permissions: All files must have mode 0655. 5. Condition: Use ansible_nodename or ansible_hostname variables.

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
cat inventory

2. Create the Playbook

I created the playbook using the copy module combined with the when conditional. This allows me to write one play for hosts: all, but selectively execute tasks.

Command: 

vi playbook.yml

Content: 

---
- name: Copy files using conditionals
  hosts: all
  become: yes
  tasks:

    - name: Show the nodename for debugging
      debug:
        msg: "Nodename is: {{ ansible_nodename }}"

    - name: Copy blog.txt to app server 1
      copy:
        src: /usr/src/devops/blog.txt
        dest: /opt/devops/blog.txt
        owner: tony
        group: tony
        mode: '0655'
      when: ansible_nodename == "stapp01.stratos.xfusioncorp.com"

    - name: Copy story.txt to app server 2
      copy:
        src: /usr/src/devops/story.txt
        dest: /opt/devops/story.txt
        owner: steve
        group: steve
        mode: '0655'
      when: ansible_nodename == "stapp02.stratos.xfusioncorp.com"    

    - name: Copy media.txt to app server 3
      copy:
        src: /usr/src/devops/media.txt
        dest: /opt/devops/media.txt
        owner: banner
        group: banner
        mode: '0655'
      when: ansible_nodename == "stapp03.stratos.xfusioncorp.com"

3. Execute and Validate

I ran the playbook against the inventory.

Command: 

ansible-playbook -i inventory playbook.yml

Output Analysis: The output clearly shows the conditional logic in action: * stapp01: Executed "Copy blog.txt", skipped "Copy story.txt", skipped "Copy media.txt". * stapp02: Skipped "Copy blog.txt", executed "Copy story.txt", skipped "Copy media.txt". * stapp03: Skipped "Copy blog.txt", skipped "Copy story.txt", executed "Copy media.txt".

Deep Dive: Ansible Concepts Used

The when Conditional

The when statement is Ansible's version of an if statement. It evaluates a Jinja2 expression. If the expression is true, the task runs. If false, the task is skipped. * Syntax: when: variable == "value" * Context: You do not need {{ }} brackets inside a when clause because it is already an implicit Jinja2 context.

Ansible Facts (ansible_nodename)

When Ansible runs (specifically the Gathering Facts task), it collects data about the remote system. * ansible_hostname: Usually just the short hostname (e.g., stapp01). * ansible_nodename or ansible_fqdn: Often the full Fully Qualified Domain Name (e.g., stapp01.stratos.xfusioncorp.com). * Debugging: The debug task I added was crucial. It revealed that ansible_nodename returned the full domain name, not just stapp01. This allowed me to fix my when condition to match the exact string.

Troubleshooting

Issue: Tasks skipped on all hosts * Cause: The conditional check didn't match. For example, checking when: ansible_nodename == "stapp01" when the actual value was stapp01.stratos.xfusioncorp.com. * Fix: Use the debug module to print the variable (msg: "{{ ansible_nodename }}") and copy the exact value into your when statement.

Issue: "Permission denied" * Cause: Writing to /opt/devops requires root privileges. * Fix: Ensure become: yes is present at the play level.