Facts¶

• In this section, we will cover Ansible Facts.
• Ansible facts are essentially “Ansible Scripts” and constitute one of the building blocks of Ansible.
• Ansible facts are data corresponding to your remote systems, which includes operating systems, IP addresses, attached filesystems, and more.
• Ansible facts are gathered, and relate to target nodes (host nodes to be configured). They are returned back to the controller node.

What will we learn?¶

• How to view and use Ansible facts
• How to use facts in playbooks for conditional logic
• How to disable fact gathering
• How to create and use custom facts

Prerequisites¶

• Complete the previous lab in order to have Ansible set up with playbooks.

01. How to View Facts?¶

• Ansible gathers facts about remote systems using the setup module.
• You can view facts of a remote machine by running the following command:

ansible all -m setup

• Example Output (Truncated for brevity):

  {
    "ansible_facts": {
      "ansible_distribution": "Ubuntu",
      "ansible_distribution_version": "22.04",
      "ansible_architecture": "x86_64",
      "ansible_memory_mb": {
        "real": {
          "total": 7989,
          "used": 2034
        }
      },
      "ansible_default_ipv4": {
        "address": "192.168.1.10",
        "netmask": "255.255.255.0",
        "gateway": "192.168.1.1"
      }
    }
  }
  

02. How to use facts in playbooks?¶

• Facts allow you to base your playbook logic on the properties of the target hosts.
• All facts are prefixed with ansible_x.
• For example, to access the operating system distribution of a host, you would use ansible_distribution.
• Here are some examples of how to use facts in playbooks:

• Example: Installing Packages Based on OS¶

  ---
  - hosts: all
    tasks:
      - name: Install Nginx on Debian using APT
        ansible.builtin.apt:
          name: nginx
          state: present
        when: ansible_distribution == "Ubuntu"
  
      - name: Install Nginx on RedHat using DNF
        ansible.builtin.dnf:
          name: nginx
          state: present
        when: ansible_distribution == "CentOS"
  

• Example: Conditional execution based on memory¶

  - name: Restart Service if Memory is Low
    ansible.builtin.service:
      name: my_service
      state: restarted
    when: ansible_memory_mb.real.total < 4000
  

03. Commonly used facts¶

System Information¶

Networking¶

Hardware¶

User-defined Facts¶

04. Disabling fact gathering¶

• By default, Ansible gathers facts before running a playbook.
• In order to disable it, add the following at the beginning of your playbook:
• To disable fact gathering, set gather_facts to no in your playbook:

- hosts: all
  gather_facts: no
  tasks:
    - name: Print a message
      debug:
        msg: "Facts gathering is disabled!"

05. Custom Facts¶

• You can define custom facts by creating .fact files, placing them inside /etc/ansible/facts.d/ directory on the managed host.

Example: Creating a custom fact¶

• Create the file /etc/ansible/facts.d/custom.fact with:

[custom]
environment=production
app_version=1.2.3

• Retrieve the fact in a playbook:

- hosts: all
  tasks:
    - debug:
        msg: "App version is {{ ansible_local.custom.app_version }}"

Using Custom Facts¶

• Another way to define your own custom facts using the set_fact module in your playbooks.
• Here is an example:

- hosts: all
  tasks:
    - name: Set custom fact
      ansible.builtin.set_fact:
        my_custom_fact: "Hello, Ansible!"
    - name: Print custom fact
      debug:
        msg: "{{ my_custom_fact }}"

06. Hands-on¶

• Use the setup module to gather and print all facts from linux-server-1.

??? success “Solution” bash ansible linux-server-1 -m setup

• Use the setup module to gather and print only the network-related facts from linux-server-2.

??? success “Solution” bash ansible linux-server-2 -m setup -a "filter=ansible_default_ipv4*"

• Create a playbook that installs nginx only if the target host is running Ubuntu.

??? success “Solution” yaml --- - hosts: all tasks: - name: Install nginx on Ubuntu ansible.builtin.apt: name: nginx state: present when: ansible_distribution == "Ubuntu"

• Create a playbook that restarts a service only if the host has less than 4GB of RAM.

??? success “Solution” yaml --- - hosts: all tasks: - name: Restart service if memory low ansible.builtin.service: name: my_service state: restarted when: ansible_memory_mb.real.total < 4096

• Create a custom fact that defines the environment as development and print it in a playbook.

??? success “Solution” First, create /etc/ansible/facts.d/custom.fact on the host:

  ```ini
  [custom]
  environment=development
  ```

  Then playbook:

  ```yaml
  ---
  - hosts: all
    tasks:
      - debug:
          msg: "Environment is {{ ansible_local.custom.environment }}"
  ```

• Create a playbook that sets a custom fact deployment_stage to staging and prints it.

??? success “Solution” yaml --- - hosts: all tasks: - name: Set custom fact ansible.builtin.set_fact: deployment_stage: staging - name: Print custom fact debug: msg: "Deployment stage: {{ deployment_stage }}"

• Disable fact gathering in a playbook and print a message indicating that facts are not gathered.

??? success “Solution” yaml --- - hosts: all gather_facts: no tasks: - name: Print message debug: msg: "Facts gathering is disabled!"

• Create a playbook that prints the hostname of each target host using the appropriate fact.

??? success “Solution” yaml --- - hosts: all tasks: - name: Print hostname debug: msg: "Hostname: {{ ansible_hostname }}"

• Create a playbook that checks the OS family and installs a package accordingly (e.g., nginx for Debian, httpd for RedHat).

??? success “Solution” yaml --- - hosts: all tasks: - name: Install nginx on Debian ansible.builtin.apt: name: nginx state: present when: ansible_os_family == "Debian" - name: Install httpd on RedHat ansible.builtin.dnf: name: httpd state: present when: ansible_os_family == "RedHat"

• Create a playbook that gathers facts and prints the total memory of each host.

??? success “Solution” yaml --- - hosts: all tasks: - name: Print total memory debug: msg: "Total memory: {{ ansible_memory_mb.real.total }} MB"

• Create a playbook that checks the default gateway and prints it.

??? success “Solution” yaml --- - hosts: all tasks: - name: Print default gateway debug: msg: "Default gateway: {{ ansible_default_ipv4.gateway }}"

• Create a playbook that sets a custom fact backup_required to yes and prints a message if backup is required.

??? success “Solution” yaml --- - hosts: all tasks: - name: Set custom fact ansible.builtin.set_fact: backup_required: yes - name: Print message if backup required debug: msg: "Backup is required" when: backup_required == "yes"

• Create a playbook that uses the ansible_user fact to print the current user on each host.

??? success “Solution” yaml --- - hosts: all tasks: - name: Print current user debug: msg: "Current user: {{ ansible_user }}"

• Print the IP addresses of all the machines.

??? success “Solution” bash ansible all -m setup -a "filter=ansible_default_ipv4.address"

• Bonus - Try printing the address of linux-server-2 only, without modifying the inventory file.

??? success “Solution” bash ansible linux-server-2 -m setup -a "filter=ansible_default_ipv4.address"

07. Summary¶

• Ansible facts provide system details dynamically.
• They are automatically gathered using the setup module.
• They are useful for conditional logic in playbooks.
• Facts may include OS, networking, CPU, memory and more.
• Custom facts can be created for customized automation.