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Ansible - Variable

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• Ansible - Variable
  • Variable
    • Variable Types
  • Variable Precedence
  • Register: Output a varialbe
  • Variable Scope
  • Magic variable
    • Magic variable - hostvars
    • Magic variable - groups
  • Ansible Fact
  • Lab: Get Fact Data

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Variable

• Variable

  • store information of the hosts

• Can be defined in

  • the playbook file
  • the a separated file

• Sematic

# define
vars:
  var_name: var_values

# reference var
line: "nameserver " # use Jinja2 Templating format

• Example

# define in variable file
http_port: 8081
snmp_port: 161-162
inter_ip_range: 192.0.2.0

# playbook file
name: Set firewall configuration
hosts: web
task:
  - firewalld:
      service: https
      permanent: true
      state: enabled
  - firewalld:
      port: ""/tcp
      permanent: true
      state: disabled
  - firewalld:
      port: ""/tcp
      permanent: true
      state: disabled
  - firewalld:
      source: ""/tcp
      permanent: internal
      state: enabled

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Variable Types

• String
• Number
  • can be integer or floating-piont
• Boolean
  • Truthly values: True 'true', 't', 'yes', 'y', 'on', '1', 1, 1.0
  • Falsy values: False 'false', 'f', 'no', 'n', 'off', '0', 0, 0.0
• List
  • ordered collection of value
  • can be any type
• Dictionary
  • key-value pairs
  • keys and values can be of any type
  • referencing value: ie.,user.name

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Variable Precedence

• When same variable is defined in multiple places

• Precedence:(highest at the bottom)

  • Role Defaults
  • Group Vars
  • Host Vars
  • Host Facts
  • Play Vars
  • Role Vars
  • Include Vars
  • Set Facts
  • Extra Vars

• ref:

  • https://docs.ansible.com/ansible/latest/reference_appendices/general_precedence.html#variables

---

• Example:
  • dns_server are defined for both group level and host level

web1 ansible_host=172.20.1.100
web2 ansible_host=172.20.1.101 dns_server=10.5.5.4 # define for this host
web3 ansible_host=172.20.1.102

[web_servers]
web1
Web2
web3

[web_servers:vars]
dns_server=10.5.5.3 # variable defined for groups to be applied for each host

dns_server of web1 and web2: 10.5.5.3 dns_server of web2: 10.5.5.4

---

• Example:
  • a dns_server defined in the playbook

- name: Configure DNS server
  hosts: all
  vars:
    dns_server: 10.5.5.5 # play level
  task:
    - nsupdate:
      server: ""

dns_server of all web host: 10.5.5.5

---

• Exmaple:
  • pass value using --extra-vars

ansible-playbook playbook.yml --extra-vars "dns_server=10.5.5.6"

all hosts included in this playbook: 10.5.5.6

---

Register: Output a varialbe

• Output a variable, using register: var_name

- name: check /etc/hosts file
  hosts: all
  tasks:
    - shell: cat /etc/hosts
      register: result # capture the output in var result
    - debug:
        var: result # assign the result to var, this print all message
        # var: result.stdout # print only the stdout message

• option: using option -v
  • ansible-playbook -i inventory playbook.yml -v

---

Variable Scope

• Scope level:
  • Host, defined within a host.
    • ie., dns_server for a host.
  • Play, defined within a play.
    • ie., ntp_server a play, cannot be accessible in another play.
  • Global, defined in configuration file, env var, cli extra-vars.
    • ie., ansible-playbook playbook.yml --extra-vars "ntp_server=10.0.0.1"

---

Magic variable

• Ansible magic variables
  • a set of predefined, immutable variables automatically provided by Ansible during playbook execution.
  • offer insights into the current state of the Ansible environment, the hosts involved, and the execution context.

Magic variable - hostvars

• Ansible process explanation

• for the following inventroy

# /etc/ansible/hosts
web1 ansible_host=172.20.1.100
web2 ansible_host=172.20.1.101 dns_server=10.5.5.4
web3 ansible_host=172.20.1.102

• Subprocesses:
  • When executing, Ansible will create 3 subprocesses for web1, web2, and web3.
• Variable Interpolation:
  • Within each subprocess, variable will be created
  • web1: inventory_hostname=web1, ansible_host=172.20.1.100
  • web2: inventory_hostname=web2, ansible_host=172.20.1.101 dns_server=10.5.5.4
  • web3: inventory_hostname=web3, ansible_host=172.20.1.102

• As a result, the host varialbes dns_server are not available for others, because it exists only within the subprocess web2.

• The magic variable hostvars can be used to share variable only in subprocess web2.

- name: Print dns server
  hosts: all
  task:
    - debug:
        msg: ""

• Common Parameters of magic variable hostvars

Parameter	Desc
hostvars['host_name'].ansible_host	Get the hostname/IP of a host
hostvars['host_name'].ansible_facts.architecture	Get the architecture of a host’s fact
hostvars['host_name'].ansible_facts.devices	Get the devices of a host’s fact
hostvars['host_name'].ansible_facts.mounts	Get the mounts of a host’s fact
hostvars['host_name'].ansible_facts.processor	Get the processor of a host’s fact

---

Magic variable - groups

Magic variable	Desc
groups['group_name']	Get all hosts under a given group
group_names	Get the group name of current host
inventory_hostname	Get the name in the inventory for the current host

---

Ansible Fact

• Ansible facts

  • a type of variable automatically gathered by Ansible about the remote systems (managed hosts) during the execution of a playbook or ad-hoc command.
  • provide detailed information about the system’s state and configuration, which can then be used in playbooks for conditional logic, task execution, or templating.

• Ref:

  • https://docs.ansible.com/ansible/latest/playbook_guide/playbooks_vars_facts.html
• gathers facts before executing tasks
  • using setup module
  • the host to be gathtered controlled by the playbook
    • a playbook for a specific host will gather fact only from the specific host, not from all hosts defined in the inventory.
• Control by
  • playbook directive gather_facts
    • default: true
    • Disabling Facts: gather_facts: false
  • Ansible configuration
    • default: gathering = implicit, gether facts automatically
    • Disabling: gathering = explicit, not gether facts when executing.
      • Can be overriden by playbook setting gather_facts: true
• Facts are stored in the ansible_facts variable

---

Lab: Get Fact Data

# inventory.yml
tee > "inventory.yaml" <<EOF
all:
  hosts:
    server1:
      ansible_host: 192.168.100.107
      ansible_user: ubuntuadmin
EOF

ansible -i inventory.yaml all -m ping

tee >get_fact_variable.yaml << EOF
- name: Ansible Fact Lab Playbook
  hosts: all
  tasks:
    - name: Print all facts
      debug:
        msg: ""

    - name: Print host facts
      debug:
        msg: "Memory:  MB, Distribution: , Architecture: "
EOF

ansible-playbook -i inventory.yaml get_fact_variable.yaml
# TASK [Print host facts] **************************************************************************
# ok: [server1] => {
#     "msg": "Memory: 7892 MB, Distribution: Ubuntu, Architecture: x86_64"
# }