Facts and Gathering Facts

# Collect and display all facts from a single host
ansible web01.example.com -m ansible.builtin.setup

# Filter to just network facts
ansible web01.example.com -m ansible.builtin.setup -a "filter=ansible_default_ipv4"

# Filter using a wildcard pattern
ansible web01.example.com -m ansible.builtin.setup -a "filter=ansible_*_mb"

- name: Install Nginx on Debian-based systems
  ansible.builtin.apt:
    name: nginx
    state: present
  when: ansible_os_family == "Debian"

- name: Install Nginx on RedHat-based systems
  ansible.builtin.dnf:
    name: nginx
    state: present
  when: ansible_os_family == "RedHat"

# Or more elegantly — use the generic package module with a fact-driven condition:
- name: Fail early if OS is not supported
  ansible.builtin.fail:
    msg: "This playbook only supports Ubuntu 20.04 and 22.04"
  when:
    - ansible_distribution != "Ubuntu"
    - ansible_distribution_major_version not in ["20", "22"]

- name: Configure Nginx worker processes based on CPU count
  ansible.builtin.template:
    src: nginx.conf.j2
    dest: /etc/nginx/nginx.conf

# In nginx.conf.j2:
# worker_processes {{ ansible_processor_vcpus }};
# This renders as "worker_processes 4;" on a 4-core server
# and "worker_processes 8;" on an 8-core server — automatically

- name: Set JVM heap size to 50% of total RAM
  ansible.builtin.set_fact:
    jvm_heap_mb: "{{ (ansible_memtotal_mb * 0.5) | int }}"
    # On a 4096 MB server: jvm_heap_mb = 2048
    # On an 8192 MB server: jvm_heap_mb = 4096
    # The same playbook configures both correctly

- name: Deploy JVM configuration
  ansible.builtin.template:
    src: jvm.options.j2
    dest: /etc/app/jvm.options
  # jvm.options.j2 contains: -Xmx{{ jvm_heap_mb }}m

# Disable gathering entirely for a fast utility play
- name: Check service health across fleet
  hosts: all
  gather_facts: false              # no facts needed — just checking service status
  tasks:
    - name: Check Nginx is running
      ansible.builtin.service_facts:
      register: service_state

    - name: Report Nginx status
      ansible.builtin.debug:
        msg: "Nginx is {{ service_state.ansible_facts.services['nginx.service'].state }}"

---
# Gather only specific fact subsets to save time
- name: Deploy with minimal fact collection
  hosts: webservers
  gather_facts: true
  gather_subset:
    - "!all"           # disable all facts
    - "network"        # then re-enable only network facts
    - "hardware"       # and hardware facts
  tasks:
    - name: Use network and hardware facts only
      ansible.builtin.debug:
        msg: "{{ ansible_default_ipv4.address }} — {{ ansible_memtotal_mb }} MB RAM"

# Step 1 — deploy a custom facts file to the managed node
- name: Create custom facts directory
  ansible.builtin.file:
    path: /etc/ansible/facts.d
    state: directory
    mode: "0755"

- name: Deploy application custom facts
  ansible.builtin.copy:
    content: |
      [application]
      name=myapp
      version=2.4.1
      environment=production
      deploy_user=deploy
    dest: /etc/ansible/facts.d/application.fact
    mode: "0644"

# Step 2 — refresh facts in the same play to make them available immediately
- name: Reload facts after deploying custom facts file
  ansible.builtin.setup:
    filter: ansible_local

# Step 3 — use the custom facts in subsequent tasks
- name: Log the deployed application version
  ansible.builtin.debug:
    msg: >
      Deployed {{ ansible_local.application.application.name }}
      version {{ ansible_local.application.application.version }}
      to {{ ansible_local.application.application.environment }}