Ansible Variables

• • Ansible variables are case-sensitive
• • Ansible variables should not have duplicate names, especially not conflict with built-in variables
• • Ansible variable names can consist of numbers, letters, and underscores, but must start with a letter

Connection Variables

Connection variables are built-in variables in Ansible that control how Ansible connects to managed hosts.

They can be set in the inventory, Playbook, and <span>ansible -e</span>.

• • ansible_host: Specifies the real IP address of the host in the inventory
• • ansible_port: Specifies the port of the host in the inventory
• • ansible_user: Specifies the connection user for the host in the inventory
• • ansible_become: Whether to escalate privileges
• • ansible_become_user: The user to escalate privileges to
• • ansible_become_password: If a password is required for privilege escalation, it can be specified with this variable
• • ansible_sudo_exec: If the sudo command is not in the default path, specify the path to the sudo command
• • ansible_connection: The type of SSH connection: local, ssh, paramiko, default is ssh
• • ansible_ssh_password: The password for SSH connection
• • ansible_ssh_private_key_file: The path to the key file, can be used if you do not want to use ssh-agent to manage the key file
• • ansible_ssh_executable: If the ssh command is not in the default path, this variable can define its path
• • ansible_ssh_extra_args: Additional SSH parameters.
• • ansible_python_interpreter: Specifies the location of Python on the managed host

Here is an example of setting variables in the inventory:

[all:vars]
ansible_ssh_user = root
ansible_ssh_password = redhat
ansible_become = true
ansible_become_user = redhat

Defining Variables

Inventory Definition

server1 MYSQL_VERSION=5.7 MYSQL_MASTER=true
[web]
server2
server3

[web:vars]
HTTPD_VERSION=2.4

[all:vars]
SYSTEM_TYPE=RHEL

• • Host variables are written after the host separated by spaces, such as MYSQL_VERSION and MYSQL_MASTER
• • Group variables are defined by appending <span>:vars</span> to the group name, such as [web:vars]
• • Variables for all hosts can be defined using [all:vars]

You can also define the inventory in YAML format

ungrouped:
  hosts:
    server1:
      MYSQL_VERSION: 5.7
      MYSQL_MASTER: true

web:
  hosts:
    server2:
    server3:
  vars:
    HTTPD_VERSION: 2.4

all:
  vars:
    SYSTEM_TYPE: RHEL

Defining and Using Variables in Ansible Playbook

Setting with vars Keyword

---
- name: set sssd
  hosts: all
  gather_facts: false
  vars:
    sssd_packages:
    - sssd
    - sssd-tools
    - oddjob
    - oddjob-mkhomedir
    - libsss_sudo
  tasks:
  - name: install packages
    ansible.builtin.yum:
      name: "{{ sssd_packages }}"

sssd_packages is the defined variable

Setting with set_fact Module

- name: set fact
  hosts: localhost
  gather_facts: false
  tasks:
  - name: set fact
    ansible.builtin.set_fact:
      var1: one
      var2:
      - two
      - three
  - name: print vars
    ansible.builtin.debug:
      msg: "{{ var1 }} and {{ var2 }} "

var1 and var2 are variables set using the <span>set_fact</span> module, and variables set with <span>set_fact</span> can be used in subsequent modules.

Setting Variables via Files

Custom Variable File

cat vars_file.yml
---
var3: three
var4: four

cat test.yml
- name: set fact
  hosts: localhost
  gather_facts: false
  vars_files:
  - ./vars_file.yml
  tasks:
  - name: print vars
    ansible.builtin.debug:
      msg: "{{ var3 }} and {{ var4 }} "

Write variables into the vars_file.yml file, and load the variable file in the playbook using vars_files

Setting Host Variables

cat host_vars/localhost/vars.yml
---
HTTPD_VERSION: 2.4
cat test.yml
- name: set fact
  hosts: localhost
  gather_facts: false
  tasks:
  - name: print vars
    ansible.builtin.debug:
      msg: "{{ HTTPD_VERSION }}"

Create a host_vars directory in the directory where the Ansible configuration file is located, and create a directory under host_vars that corresponds to the name or address in the inventory, such as <span>./host_vars/localhost/</span> (indicating setting variables for the <span>localhost</span> host), and create any file under <span>./host_vars/localhost/</span> (the file can be named anything, preferably ending with <span>.yml</span> or <span>.yaml</span> for easy viewing), write variables into the file, such as <span>./host_vars/localhost/vars.yml</span>, Ansible will automatically read the files in the same-named directory, and the Playbook can directly reference the variables.

Setting Group Variables

cat inventory
[webserver]
server1
server2
cat group_vars/webserver/vars.yml
---
SYSTEM_TYPE: RHEL
cat test.yml
- name: set fact
  hosts: webserver
  gather_facts: false
  tasks:
  - name: print vars
    ansible.builtin.debug:
      msg: "{{ SYSTEM_TYPE }}"

Similar to host_vars, but the host is replaced with a group.

Registering Variables

cat test.yml
- name: set fact
  hosts: webserver
  gather_facts: false
  tasks:
  - name: register
    ansible.builtin.command: id
    register: register_var
  - name: print vars
    ansible.builtin.debug:
      msg: "{{ register_var }}"

After the module executes successfully, you can use <span>register</span> to register the output as a variable, the registered variable output is as follows

ok: [server1] => {
    "msg": {
        "ansible_facts": {
            "discovered_interpreter_python": "/usr/libexec/platform-python"
        },
        "changed": true,
        "cmd": [
            "id"
        ],
        "delta": "0:00:00.004153",
        "end": "2024-08-04 23:09:14.460466",
        "failed": false,
        "msg": "",
        "rc": 0,
        "start": "2024-08-04 23:09:14.456313",
        "stderr": "",
        "stderr_lines": [],
        "stdout": "uid=0(root) gid=0(root) groups=0(root) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023",
        "stdout_lines": [
            "uid=0(root) gid=0(root) groups=0(root) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023"
        ]
    }
}

Here are some valuable outputs: <span>failed</span>, <span>rc</span>, <span>stderr</span>, <span>stderr_lines</span>, <span>stdout</span>, and <span>stdout_lines</span>, these outputs can be used to determine whether the execution was successful and for subsequent modules to reference the content of this execution result.

Setting Variables via Ansible Ad-Hoc

ansible localhost -e SYSTEM_TYPE=RHEL -m debug -a 'msg="{{ SYSTEM_TYPE }}"'

Use the <span>-e</span> option to set variables, with highest priority.

Referencing Variables in Ansible Playbook

Referencing with {{}}

---
- name: set sssd
  hosts: all
  gather_facts: false
  vars:
    sssd_packages:
    - sssd
    - sssd-tools
    - oddjob
    - oddjob-mkhomedir
    - libsss_sudo
  tasks:
  - name: install packages
    ansible.builtin.yum:
      name: "{{ sssd_packages }}"

<span>"{{ sssd_packages }}"</span> is the way to reference a variable, if there are multiple variables, it is written as follows <span>"{{ var1 }} {{ var2 }}"</span>

When using variables in a playbook, pay attention to the use of double quotes. If a paragraph starts with a variable call, i.e., starts with <span>{{</span>, then that paragraph needs to be enclosed in double quotes, but if it starts with a string, then double quotes can be omitted.

---
- name: vars example
  hosts: all
  vars:
    var1: one
    var2: two
  tasks:
  - name: debug1
    ansible.builtin.debug:
      msg: vars is {{ var1 }} and {{ var2 }}
  - name: debug2
    ansible.builtin.debug:
      msg: "{{ var1 }} and {{ var2 }}"

The template module can also use variables, in the same way as above.

Referencing with []

<span>[]</span> references differ from <span>{{}}</span> in that the values inside <span>[]</span> are treated as variables. For example:

---
- name: test
  hosts: localhost
  vars:
    netcard: ens18
  tasks:
  - name: loop list
    debug:
      msg: "{{ ansible_facts[netcard].ipv4.address }}"

The above <span>"{{ ansible_facts[netcard].ipv4.address }}"</span> uses <span>[]</span>, and <span>netcard</span> will also be treated as a variable, the actual variable to print is <span>ansible_facts.ens18.ipv4.address</span>.

In some cases, when referencing variables, <span>['']</span> is used, which does not treat the value inside as a variable. For example: <span>ansible_facts['ens18'].ipv4.address</span> is <span>ansible_facts.ens18.ipv4.address</span>.

Note that when using <span>[]</span>, there is no <span>.</span> on the left side, for example: <span>ansible_facts[netcard].ipv4['address']</span>.