Conditionals

Updated Jan 06, 2021 ·

Overview

This lab practices Ansible conditionals so tasks run only when host or variable conditions match.

Inventory

# We have created a group for web servers. Similarly create a group for database servers named 'db_servers' and add db1 server to it
# --------------------------------
# Sample Inventory File

# Web Servers
web1 ansible_host=server1.company.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Password123!
web2 ansible_host=server2.company.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Password123!
web3 ansible_host=server3.company.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Password123!

# Database Servers
db1 ansible_host=server4.company.com ansible_connection=winrm ansible_user=administrator ansible_ssh_pass=Password123!

[web_servers]
web1
web2
web3

[db_servers]
db1

Task 1

The given playbook attempts to start mysql service on all_servers. Use the when condition to run this task if the host (ansible_host) is the database server.

Refer to the inventory file to identify the name of the database server.

Task 2

The playbook has a variable defined - age. The two tasks attempt to print if I am a child or an Adult. Use the when conditional to print if I am a child or an Adult based on weather my age is < 18 (child) or >= 18 (Adult).

Task 3

The given playbook attempts to add an entry into the /etc/resolv.conf file for nameserver.

First, we run a command using the shell module to get the contents of /etc/resolv.conf file and then we add a new line containing the name server data into the file. However, when this playbook is run multiple times, it keeps adding new entries of same line into the resolv.conf file.

Add a register directive to store the output of the first command to variable command_output

Then add a conditional to the second command to check if the output contains the name server (10.0.250.10) already. You can use:

command_output.stdout.find("10.0.250.10") == -1

Note: A better way to do this would be to use the lineinfile module. This is just for practice.

Note: shell and command modules are similar in that they are used to execute a command on the system. However shell executes the command inside a shell giving us access to environment variables and redirection using >>

Solutions

Solution 1

---

- name: 'Execute a script on all web server nodes'
  hosts: all_servers
  tasks:
  - service: 'name=mysql state=started'
    when: 'ansible_host=="server4.company.com"'

Solution 2

---

- name: 'Am I an Adult or a Child?'
  hosts: localhost
  vars:
      age: 25
  tasks:  
  - command: 'echo "I am a Child"'
    when: 'age < 18'
    
  - command: 'echo "I am an Adult"'
    when: 'age >= 18'   

Solution 3

---

- name: 'Add name server entry if not already entered'
  hosts: localhost
  tasks:
  - shell: 'cat /etc/resolv.conf'
    register: command_output
    
  - shell: 'echo "nameserver 10.0.250.10" >> /etc/resolv.conf'
    when: 'command_output.stdout.find("10.0.250.10") == -1'

Overview​

Overview