Ansible variables are used to store values that can be reused across tasks, plays, or templates. They come in different types and scopes. Here’s a detailed breakdown:

1. Based on Scope / Where Defined

Variable Type	Description	Example
Inventory variables	Defined per host or group in the inventory file.	`db_servers ansible_host=192.168.0.156 ansible_user=oracle`
Host variables	Specific to a host, usually in the `host_vars/<hostname>` folder.	`/host_vars/oe101db.yml`: `db_name: SSRDB`
Group variables	Shared across a group, usually in the `group_vars/<groupname>` folder.	`/group_vars/db_servers.yml`: `oracle_home: /u01/app/oracle`
Play variables	Defined inside a play in the playbook under the `vars:` keyword.	`vars: sga_size: 3GB pga_size: 1GB`
Task variables	Defined for a single task using the `vars:` keyword.	`name: Create DB tablespace vars: ts_name: USERS`
Registered variables	Store the output of a task for reuse later using the `register:` keyword.	`command: "hostname" register: host_out`
Extra variables	Passed at runtime using the `-e` or `--extra-vars` command-line option.	`ansible-playbook play.yml -e "env=prod db_name=SSRDB"`

2. Based on Data Type

Type	Description	Example
String	Sequence of characters.	`db_name: SSRDB`
Integer	Numbers.	`port: 1521`
Float	Decimal numbers.	`threshold: 0.75`
Boolean	True/False values.	`enabled: true`
List (array)	Sequence of items.	`disks: ["/u01", "/u02", "/u03"]`
Dictionary (hash/map)	Key-value pairs.	`yaml users: user1: oracle user2: grid`
Complex / Nested	List of dictionaries or nested structures.	`yaml databases: - name: SSRDB sga: 3GB - name: TESTDB sga: 1GB`

3. Automatic/Magic Variables (Facts and Special)

Variable	Description
`ansible_hostname`	Hostname of the target machine.
`inventory_hostname`	Hostname as defined in inventory.
`ansible_os_family`	OS family (RedHat, Debian).
`ansible_user`	Remote user used to connect.
`ansible_all_ipv4_addresses`	List of IPv4 addresses.
`ansible_playbook_dir`	Directory of the current playbook.
`hostvars`	Access variables of another host.
`groups`	Access hosts in a group.

A simple example.

[oracle@oel01db ansible-project]$ cat ./playbooks/var_demo.yml

- hosts: db_servers

vars:

db_name: SSRDB

sga_size: 3GB

tasks:

- name: Print DB name

debug:

msg: "Database name is {{ db_name }} with SGA {{ sga_size }}"

[oracle@oel01db ansible-project]$

[oracle@oel01db ansible-project]$ ansible-playbook -i ./inventory/hosts ./playbooks/var_demo.yml

PLAY [db_servers] ******************************************************************************************************************************************************************************************************************

TASK [Gathering Facts] *************************************************************************************************************************************************************************************************************

ok: [192.168.0.156]

TASK [Print DB name] ***************************************************************************************************************************************************************************************************************

ok: [192.168.0.156] => {

"msg": "Database name is SSRDB with SGA 3GB"

}

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

192.168.0.156 : ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0

[oracle@oel01db ansible-project]$

Once you define a variable there are different way to refer it

Method	Example	Use case
`{{ region }}`	`msg: "{{ region }}"`	Most common
`vars['region']`	`msg: "{{ vars['region'] }}"`	Dynamic variable names
`hostvars`	`hostvars['host1']['region']`	Access variable of another host
`set_fact`	`my_region: "{{ region }}"`	Create/rename variable
`Loops`	`loop: ["{{ region }}"]`	Use in iteration

An example using postgres database setup

I've installed postgres on my managed node(192.168.0.156) , lets use this set up for learning variables.

[oracle@oel01db ansible-project]$ psql -h 192.168.0.156 -p 5432 -U postgres -d postgres

Password for user postgres:

psql (15.13)

Type "help" for help.

postgres=#

✅ Playbook to check postgres info


[oracle@oel01db ansible-project]$ cat ./playbooks/postgres_db_info.yml

---
- name: Connect to PostgreSQL database using variables
  hosts: db_servers
  gather_facts: no
  become: yes
  become_user: postgres

  vars:
    db_hostname: "{{ inventory_hostname }}"
    db_name_to_check: "postgres"
    db_port_number: 5432

  tasks:

    - name: Check status of the 'postgres' database
      community.postgresql.postgresql_info:
        login_host: "{{ db_hostname }}"  # Use login_host instead of host
        login_port: "{{ db_port_number }}" # Use login_port instead of port
        login_db: "{{ db_name_to_check }}" # Use login_db instead of db
        login_user: "postgres"
        login_password: "postgres"
      register: postgres_status

    - name: Display connection result
      debug:
        msg: >
          Successfully connected to {{ db_name_to_check }} on {{ db_hostname }}.
          Database size: {{ postgres_status.databases[db_name_to_check].size }}
[oracle@oel01db ansible-project]$
[oracle@oel01db ansible-project]$

community.postgresql.postgresql_info:

This is an Ansible module from the community.postgresql collection.

Purpose: gather information about PostgreSQL databases.

Can return database size, owners, encoding, tables, etc.

The result is stored in a variable (register: postgres_status).

For this to playbook to work we need to install

1) Ensure community.postgresql collection is installed

Run on your control node:


ansible-galaxy collection install community.postgresql

(PostgreSQL modules are not included by default.)

2) Make sure the host has `psycopg2` package

On the managed node (target DB server):


sudo yum install python3-psycopg2 -y

[oracle@oel01db ansible-project]$ ansible-playbook -i ./inventory/hosts ./playbooks/postgres_db_info.yml

PLAY [Connect to PostgreSQL database using variables] ***************************************************************************************************************************************************************************************

TASK [Check status of the 'postgres' database] **********************************************************************************************************************************************************************************************

fatal: [192.168.0.156]: FAILED! => {"ansible_facts": {"discovered_interpreter_python": "/usr/bin/python"}, "changed": false, "msg": "Failed to import the required Python library (psycopg2) on oel02db.mydb.com's Python /usr/bin/python. Plase read module documentation and install in the appropriate location. If the required library is installed, but Ansible is using the wrong Python interpreter, please consult the documentation on ansible_python_interpreter"}

192.168.0.156 : ok=0 changed=0 unreachable=0 failed=1 skipped=0 rescued=0 ignored=0

[oracle@oel01db ansible-project]$

What’s happening

You installed python3-psycopg2 on the managed host.
Ansible, by default, is using /usr/bin/python (likely Python 2.7) on that host:


"discovered_interpreter_python": "/usr/bin/python"

Python 2 doesn’t have psycopg2 installed, so the module fails.

Installing python3-psycopg2 alone is not enough unless Ansible uses Python 3.

postgres@oel02db:~$ /usr/bin/python --version

Python 2.7.5

postgres@oel02db:~$ /usr/bin/python3 --version

Python 3.6.8

postgres@oel02db:~$

Solution: Tell Ansible to use Python 3

Option 1: Set in inventory

Edit your inventory for the db host:


[db_servers]
192.168.0.156 ansible_python_interpreter=/usr/bin/python3

Option 2: Set in the playbook

Add at the top under vars::


vars:
  ansible_python_interpreter: /usr/bin/python3
  db_hostname: "{{ inventory_hostname }}"
  db_name_to_check: "postgres"
  db_port_number: 5432

 I updated my playbook.

[oracle@oel01db ansible-project]$ vi ./playbooks/postgres_db_info.yml

[oracle@oel01db ansible-project]$ cat ./playbooks/postgres_db_info.yml | grep -i ansible_python_interpreter

ansible_python_interpreter: /usr/bin/python3

[oracle@oel01db ansible-project]$

[oracle@oel01db ansible-project]$ ansible-playbook -i ./inventory/hosts ./playbooks/postgres_db_info.yml

ok: [192.168.0.156]

TASK [Display connection result] ************************************************************************************************************************************************************************************************************

ok: [192.168.0.156] => {

"msg": "Successfully connected to postgres on 192.168.0.156. Database size: 91198255\n"

}

192.168.0.156 : ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0

[oracle@oel01db ansible-project]$

devopsbasic

Saturday, 6 December 2025

Ansible 11. Variables - classification

3. Automatic/Magic Variables (Facts and Special)

✅ Playbook to check postgres info

2) Make sure the host has `psycopg2` package

What’s happening

Solution: Tell Ansible to use Python 3

Option 1: Set in inventory

Option 2: Set in the playbook

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Building a Safer PostgreSQL CI/CD Pipeline with GitHub Actions: Dev → PR Review → Test Promotion

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Saturday, 6 December 2025

Ansible 11. Variables - classification

3. Automatic/Magic Variables (Facts and Special)

✅ Playbook to check postgres info

2) Make sure the host has psycopg2 package

What’s happening

Solution: Tell Ansible to use Python 3

Option 1: Set in inventory

Option 2: Set in the playbook

No comments:

Post a Comment

Building a Safer PostgreSQL CI/CD Pipeline with GitHub Actions: Dev → PR Review → Test Promotion

2) Make sure the host has `psycopg2` package