Ansible Variables

 Variables

Variables can be used in tasks, as well as in template files.

You reference variables by using {{ variable }}. Ansible replaces this {{ variable }} with the value of the variable value

eg

vars:

conf_file: /etc/nginx/sites/default

Ansible will substitute "{{ conf_file }}" with /etc/nginx/sites/default when it executes this task.

Ansible uses the Jinja2 template engine to implement templating

We use the .j2 extension to indicate that the file is a Jinja2 template. However, we can use a any extension if you like.

Ansible also uses the Jinja2 template engine to evaluate variables in playbooks.

Loop

When you want to run a task with each item from a list, you can use loop.

A loop executes the task multiple times, each time replacing item with different values from the specified list.

Handlers

Handlers are one of the conditional forms, A handler is similar to a task, but it runs only if it has been notified by a task. A task will run the notification if Ansible recognizes that the task was changed.

handlers:

- name: Restart nginx

service:

name: nginx

state: restarted

- name: Manage nginx

template:

src:

dest:

notify: Restart nginx

Handlers usually run at the end of the play after all of the tasks have been run.

To force a notified handler in the middle of a play, we need to use flush_handlers

- name: Restart nginx

meta: flush_handlers

If a play contains multiple handlers, the handlers always run in the order that they are defined in the handlers section, not the notification order.

They run only once, even if they are notified multiple times.

Variables in Separate Files

vars_files:

- nginx.yml

viewing the value of variables

To view the values of variables, you can use the debug module. The debug module allows you to print the value of a variable to the console during playbook execution.

- name: Print the value of a variable

debug:

var: variable_name

- debug: var=myvarname

Variable Interpolation

- name: Display the variable

debug:

msg: "The file used was {{ conf_file }}"

Variables can be concatenated between the double braces by using the tilde operator ~, as shown here:

- name: Concatenate variables

debug:

msg: "The URL is https://{{ server_name ~'.'~ domain_name }}/"

Registering Variables

The register keyword allows you to capture the output of a task and store it in a variable for later use.

- name: Capture output of whoami command

command: whoami

register: login

Example of using register to capture the output of a command and then display it using the debug module:

---

- name: Show return value of command module

hosts: fedora

gather_facts: false

tasks:

- name: Capture output of id command

command: id -un

register: login

- debug: var=login

- debug: msg="Logged in as user {{ login.stdout }}"

...

Output of the above playbook:

TASK [Capture output of id command] ******************************************************************************************

changed: [localhost]

TASK [debug] ****************************************************************************************************************

ok: [localhost] => {

"login": {

"changed": true,

"cmd": ["id", "-un"],

"delta": "0:00:00.003123",

"end": "2024-06-01 12:00:00.000000",

"rc": 0,

"start": "2024-06-01 12:00:00.000000",

"stderr": "",

"stdout": "user"

}

}

TASK [debug] ****************************************************************************************************************

ok: [localhost] => {

"msg": "Logged in as user user"

}

The changed key is present in the return value of all Ansible modules, and Ansible uses it to determine whether a state change has occurred. For the command and shell modules, this will always be set to true unless overridden with the changed_when clause

- name: Capture output of whoami command

command: whoami

register: login

changed_when: false

The cmd key contains the invoked command as a list of strings.

The rc key contains the return code. If it is nonzero, Ansible willassume the task failed to execute successfully.

The stderr key contains any text written to standard error, as a single string.

The stdout key contains any text written to standard out, as a single string.

The stdout_lines key contains any text written to split by newlines, as a list of strings.

ACCESSING DICTIONARY KEYS IN A VARIABLE

If a variable contains a dictionary, you can access the keys of the dictionary by using either a dot (.) or a subscript ([])

{{ result.stat }}

{{ result['stat'] }}

result['stat']['mode']

result['stat'].mode

result.stat['mode']

result.stat.mode

- name: Display result.stat detail

debug: var=result['stat'][stat_key]

- name: Access dictionary keys using dot notation

debug:

msg: "The command was {{ login.cmd }} and the return code was {{ login.rc }}"

- name: Access dictionary keys using subscript notation

debug:

msg: "The command was {{ login['cmd'] }} and the return code was {{ login['rc'] }}"