Ansible Facts — Gather System Info

---
- name: Show facts
  hosts: all
  # gather_facts: true (default)
  tasks:
    - name: Print OS
      ansible.builtin.debug:
        msg: "{{ ansible_distribution }} {{ ansible_distribution_version }}"
      # Output: "Ubuntu 24.04" or "RedHat 9.3"

# Show all facts for a host
ansible myhost -m setup

# Filter specific facts
ansible myhost -m setup -a "filter=ansible_distribution*"

# Show network facts
ansible myhost -m setup -a "filter=ansible_default_ipv4"

- name: Dump all facts
  ansible.builtin.debug:
    var: ansible_facts

- name: Show specific facts
  ansible.builtin.debug:
    msg:
      os: "{{ ansible_distribution }} {{ ansible_distribution_version }}"
      ip: "{{ ansible_default_ipv4.address }}"
      cpus: "{{ ansible_processor_vcpus }}"
      ram_mb: "{{ ansible_memtotal_mb }}"
      disk: "{{ ansible_mounts | selectattr('mount', 'equalto', '/') | map(attribute='size_total') | first | human_readable }}"

---
- name: OS-specific tasks
  hosts: all
  tasks:
    # Package management by OS family
    - name: Install packages (Debian/Ubuntu)
      ansible.builtin.apt:
        name: "{{ item }}"
        state: present
      loop:
        - nginx
        - python3-pip
      when: ansible_os_family == "Debian"

    - name: Install packages (RHEL/CentOS/Fedora)
      ansible.builtin.dnf:
        name: "{{ item }}"
        state: present
      loop:
        - nginx
        - python3-pip
      when: ansible_os_family == "RedHat"

    # Version-specific logic
    - name: Ubuntu 24.04+ specific config
      ansible.builtin.template:
        src: ubuntu24.conf.j2
        dest: /etc/myapp.conf
      when:
        - ansible_distribution == "Ubuntu"
        - ansible_distribution_major_version | int >= 24

    # Architecture check
    - name: Download binary for correct architecture
      ansible.builtin.get_url:
        url: "https://releases.example.com/app-{{ ansible_architecture }}.tar.gz"
        dest: /tmp/app.tar.gz

    # Memory-based decisions
    - name: Configure for high-memory servers
      ansible.builtin.set_fact:
        db_cache_size: "{{ (ansible_memtotal_mb * 0.7) | int }}m"
      when: ansible_memtotal_mb > 4096

    - name: Configure for low-memory servers
      ansible.builtin.set_fact:
        db_cache_size: "512m"
      when: ansible_memtotal_mb <= 4096

# Generated by Ansible for {{ ansible_fqdn }}
# OS: {{ ansible_distribution }} {{ ansible_distribution_version }}
# CPUs: {{ ansible_processor_vcpus }}

worker_processes {{ ansible_processor_vcpus }};

events {
    worker_connections {{ (ansible_memtotal_mb / 4) | int }};
}

http {
    server {
        listen 80;
        server_name {{ ansible_fqdn }};

        # Access log includes hostname for multi-server setups
        access_log /var/log/nginx/{{ ansible_hostname }}-access.log;
    }
}

---
- name: Quick task (no facts needed)
  hosts: all
  gather_facts: false
  tasks:
    - name: Restart service
      ansible.builtin.service:
        name: myapp
        state: restarted

---
- name: Gather minimal facts
  hosts: all
  gather_facts: false
  tasks:
    - name: Gather only network facts
      ansible.builtin.setup:
        gather_subset:
          - network
          - "!all"

    - name: Gather everything except hardware (faster)
      ansible.builtin.setup:
        gather_subset:
          - "!hardware"

[general]
app_version=2.1.0
environment=production
deploy_date=2026-04-12

[database]
host=db.internal
port=5432

{
  "app_version": "2.1.0",
  "environment": "production"
}

#!/bin/bash
echo '{"disk_usage": "'$(df -h / | tail -1 | awk '{print $5}')'"}'

- name: Use custom facts
  ansible.builtin.debug:
    msg: "App version: {{ ansible_local.myapp.general.app_version }}"

---
- name: Deploy custom facts
  hosts: all
  become: true
  tasks:
    - name: Create facts directory
      ansible.builtin.file:
        path: /etc/ansible/facts.d
        state: directory
        mode: "0755"

    - name: Deploy custom fact file
      ansible.builtin.template:
        src: myapp.fact.j2
        dest: /etc/ansible/facts.d/myapp.fact
        mode: "0644"

    - name: Re-read facts after deploying
      ansible.builtin.setup:
        filter: ansible_local

# ansible.cfg
[defaults]
gathering = smart          # Only gather facts if not cached
fact_caching = jsonfile     # Cache backend
fact_caching_connection = /tmp/ansible-facts-cache
fact_caching_timeout = 3600 # Cache for 1 hour (seconds)

# Redis caching
[defaults]
fact_caching = redis
fact_caching_connection = localhost:6379:0
fact_caching_timeout = 7200

# These can differ!
- ansible.builtin.debug:
    msg:
      ansible_hostname: "{{ ansible_hostname }}"           # web-01
      inventory_hostname: "{{ inventory_hostname }}"       # 10.0.0.5 (if IP in inventory)

- name: Gather network facts explicitly
  ansible.builtin.setup:
    gather_subset:
      - network

- name: Use with fallback
  ansible.builtin.debug:
    msg: "{{ ansible_default_ipv4.address | default('unknown') }}"

# Option 1: Disable entirely
gather_facts: false

# Option 2: Gather only what you need
- ansible.builtin.setup:
    gather_subset:
      - "!all"
      - "!min"
      - network

# Option 3: Use fact caching (see above)

# Must be in /etc/ansible/facts.d/
# Must end in .fact
# Must be valid INI, JSON, or executable returning JSON
# Must be readable (chmod 644 for files, 755 for scripts)