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Mapagam

Working with Magic Variables

1. Using hostvars

Variable Description Example Value
hostvars Dictionary containing variables for all hosts in the inventory {"web01": {"ansible_host": "192.168.1.10", "ansible_user": "admin"}, "db01": {"ansible_host": "192.168.1.11", "ansible_user": "dbadmin"}}
hostvars['hostname'] Access variables for a specific host {"ansible_host": "192.168.1.10", "ansible_user": "admin"}

Example: Accessing host-specific variables

- name: Display host-specific variables
  debug:
    msg: "Host {{ inventory_hostname }} has IP {{ hostvars[inventory_hostname].ansible_host }}"

2. Using inventory_hostname

Property Description Example
inventory_hostname The name of the host as defined in the inventory web01
inventory_hostname_short The short name of the host (before any underscores) web

Example: Using inventory_hostname in a task

- name: Create directory with host-specific name
  file:
    path: "/tmp/{{ inventory_hostname }}"
    state: directory

Example: Using inventory_hostname_short in a task

- name: Set up environment based on host type
  set_fact:
    env_prefix: "{{ inventory_hostname_short }}_"

3. Using inventory_hostname_short

Property Description Example
inventory_hostname_short Short name of the inventory host, without any domain suffixes. web01

Example: Using inventory_hostname_short in a task

- name: "Set hostname variable"
  set_fact:
    host_name: "{{ inventory_hostname_short }}"

4. Using group_names

Property Description Example
group_names List of all group names the host belongs to ["web", "production"]

Example: Using group_names in a Playbook

- name: "Display group names"
  hosts: all
  tasks:
    - name: "Print group names"
      debug:
        msg: "Host belongs to groups: {{ group_names }}"
Note: group_names is a read-only variable and cannot be modified.

5. Using groups

Variable Description Example Value
groups All group names and their hosts {"all": ["web1", "db1"], "web": ["web1"], "db": ["db1"]}
group_names Current host's group names ["web"]
group_all All hosts in the inventory ["web1", "db1"]

Example: Accessing group members

- name: Display all hosts in the web group
  debug:
    msg: "Web servers: {{ groups['web'] }}"

Example: Using group names in conditionals

- name: Configure web server
  command: systemctl start nginx
  when: "'web' in group_names"

6. Using ansible_play_hosts

Variable Description Usage
ansible_play_hosts List of all hosts in the current play Used to iterate over all hosts or check membership in a play

Example: Looping over all hosts in a play

- name: Loop over all hosts in the play
  debug:
    msg: "Processing host: {{ item }}"
  loop: "{{ ansible_play_hosts }}"

Example: Check if a host is part of the play

- name: Verify host is in play
  debug:
    msg: "Host {{ inventory_hostname }} is part of the play"
  when: inventory_hostname in ansible_play_hosts

7. Using ansible_play_batch

Variable Description Example Value
ansible_play_batch Contains the list of hosts in the current play's batch ["host1", "host2", "host3"]

Example: Using ansible_play_batch in a Playbook

- name: Display hosts in current batch
  hosts: all
  tasks:
    - name: Show current batch
      debug:
        msg: "Current batch: {{ ansible_play_batch }}"

8. Using playbook_dir

Variable Description Example Value
playbook_dir Directory containing the playbook file being executed /home/user/ansible/playbooks/webapp

Example: Reading playbook_dir in a task

- name: Show playbook directory
  debug:
    msg: "This playbook is located in {{ playbook_dir }}"
Note: The playbook_dir variable is particularly useful when you need to reference files relative to the playbook's location, such as including templates or configuration files.

9. Using role_path

Variable Description Example Value
role_path Path to the current role's directory /etc/ansible/roles/myapp

Example: Accessing role_path in a task

- name: Display role path
  debug:
    msg: "Current role is located at {{ role_path }}"
Note: The role_path variable is automatically set by Ansible when executing tasks within a role context. It provides the absolute path to the directory where the current role is stored.

10. Using ansible_version

Variable Description Example Value
ansible_version Version of Ansible currently running 2.16.5

Example: Display Ansible Version

- name: Display Ansible version
  debug:
    msg: "Running Ansible version {{ ansible_version }}"
Note: The ansible_version variable is particularly useful for conditional logic or logging within playbooks to ensure compatibility with specific Ansible features or bug fixes.

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