Deep dive with Ansible variables

Variables in any programming language plays a very important role for customizing and optimizing the code which also improve readability .

Ansible support  variables that can store values which and be reused in files or we can say variables can provide a more convenient way to store dynamic values .

Most useful cases:

1.  storing  users name
2.  storing packages name
3.  used in loops and conditional statement 

Sample playbook example :

i)    using with copy module 

root@xpert:/etc/ansible/playbooks# cat  vars.yml 

---

 - hosts: localhost

   remote_user: xpert

   vars:

    x: "hello Google "

   tasks:

    - name: testing hello vars 

      copy: content="{{ x }}" dest=/etc/motd

ii)   creating user

root@xpert:/etc/ansible/playbooks# cat  user.yml 

---

 - hosts: localhost

   remote_user: xpert

   vars:

    x: "dream"

   tasks:

    - name: testing hello vars 

      user: 

         name="{{ x }}" 

         state=present 

         shell=/bin/bash 

         password="$1$9y7.D67S$1YUykTsDFaZjyQUg8wjvo0"

Important :   Overriding  variables 

root@xpert:/etc/ansible/playbooks# ansible-playbook  user.yml  -e "x=adhoc"

PLAY ***************************************************************************

TASK [setup] *******************************************************************

ok: [localhost]

TASK [testing hello vars] ******************************************************

changed: [localhost]

PLAY RECAP *********************************************************************

localhost                  : ok=2    changed=1    unreachable=0    failed=0   

IMportant :  Defining  variables in Inventory  with group variables

[root@station147 user]# cat   /etc/ansible/hosts

[dc]
192.168.10.121
192.168.10.65
[dc:vars]
username=root1
password=$1$hJTfjIRI$N75O5l2yGXEVl86MduBoj0

Note:  we can use these variables in you playbooks

------------------------------

[root@station147 user]# cat   /etc/ansible/playbooks/uservarsfile.yml
---
 - hosts: all
   tasks:
    - name: adding user with passowrd
      user: name="{{ username }}" password="{{ password }}"  shell=/bin/bash state=present


Note:   Nested group variables

 [root@station147 user]# cat   /etc/ansible/hosts
[ub]
192.168.10.121

[red]
192.168.10.65

[nested:children]
red
ub
[nested:vars]
username=nupppp
password=$1$hJTfjIRI$N75O5l2yGXEVl86MduBoj0

Important :

Final use case :

i)  Inventory file

[root@station147 user]# cat /etc/ansible/hostgroupvars

[ub]
192.168.10.121

[red]
192.168.10.65

[nested:children]
red
ub







ii)    playbook

[root@station147 user]# cd /etc/ansible/playbooks/user/

[root@station147 user]# cat uservarsfile.yml
---
 - hosts: all
   tasks:
    - name: adding user with passowrd
      user: name="{{ username }}" password="{{ password }}"  shell=/bin/bash state=present

iii)  group and host variables

[root@station147 user]# cat  group_vars/nested  
username: ashutoshhh2
password: redhat3
[root@station147 user]# cat host_vars/192.168.10.65
username: hacked
password: google

Important :   This type of work flow generally work with Cisco and other networking devices

Define  category :

These variables can be define into 3 category 

1.  Global scope
2.  Play scope 
3.   Host scope 

Register variables :

To store the output of running module and play then debug to dump it back on the screen
[root@localhost apache]# cat  web.yml
---
 - hosts: all
   vars:
    - x: httpd
   tasks:
    - name: Installing web server
      yum: name="{{ x }}" state=present
      register: outputvar
     
    - debug: var=outputvar

#  Magic variable :-

as we know to use variables either we need to define or need to extract from facts .

but there are some variables that can be used without defining although they are not even facts 


4  magic  variables:


i)  hostvars
Contains the variables for managed hosts, and can be used to get the values for another
managed host's variables. It won't include the managed host's facts if they haven't been
gathered yet for that host. 

Example: 

-bash-4.3$ ansible all  -m debug -a "var=hostvars"

192.168.10.55 | SUCCESS => {
    "hostvars": {
        "192.168.0.10": {
            "ansible_check_mode": false,
            "ansible_playbook_python": "/usr/bin/python2",
            "ansible_version": {
                "full": "2.4.1.0",
                "major": 2,
                "minor": 4,
 



ii)  group_namesLists all groups the current managed host is in. 



Example:

-bash-4.3$ ansible all  -m debug -a "var=group_names"
192.168.10.55 | SUCCESS => {
    "group_names": [
        "a",
        "c"
    ]
}
192.168.0.10 | SUCCESS => {
    "group_names": [
        "b",
        "c"
    ]
}


iii)  groups
Lists all groups and hosts in the inventory.


Example:

-bash-4.3$ ansible all  -u code -b -m debug -a "var=groups"
192.168.10.55 | SUCCESS => {
    "groups": {
        "a": [
            "192.168.10.55"
        ],
        "all": [
            "192.168.10.55",
            "192.168.0.10"
        ],
        "b": [
            "192.168.0.10"
        ],
        "c": [
            "192.168.10.55",
            "192.168.0.10"
        ],
        "ungrouped": []
    }
}


iv)    inventory_hostname

Contains the hostname for the current managed host as configured in the inventory. This
may be different from the hostname reported by facts for various reasons.
There are a number of other "magic variables" as well. For more information, see http://
docs.ansible.com/ansible/playbooks_variables.html. One way to get insight into their values is to
use the debug module to report on the contents of the hostvars variable for a particular host:



Using include option :


##  main playbook

-bash-4.3$ cat  playbook.yml
---
 - hosts: localhost
   become: true
   tasks:
    - name: including variables
      include_vars: vars/var.yml

    - name: task include
      include: tasks/env.yml

##  now  var.yml

-bash-4.3$ cat  vars/var.yml ---
firewall_pkg: firewalld
package: httpd
service: httpd
svc_state: started
 


## now   env.yml


-bash-4.3$ cat tasks/env.yml
---
  - name: installing  the {{ package }} package
    dnf:
     name: "{{ package }}"
     state: installed

  - name: starting the {{ service}}   service
    service:
     name: "{{ service }}"
     state: "{{ svc_state }}"