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Ansible is an automation tool used for configuration management using human-readable YAML templates. Ansible is distinguished for being agentless, meaning no special software is required on the nodes it manages.

Ansible playbooks represent a sequence of scripted actions which apply changes uniformly over a set of hosts. Modules are standalone scripts that enable a particular task across many OSes, services, applications, etc. Predefined modules are available in the module library, and new ones can be defined via Python or JSON.

Ansible host management relies on a .ini file containing a list of IP addresses or hostnames organized in groups.

There are several areas where Ansible can be used in personal projects for learning purposes. ^ref

1. Use the users module to manage users, assign groups, and define custom aliases in the profile property.
2. Put a time limit on the availability of the sudo command
3. Use Ansible Tower to produce a GUI interface to restart certain services.
4. Use Ansible Tower to look for files larger than a particular size in a directory.
5. Debug a system performance problem.

Syntax

Ansible can be used in one of two ways:

1. Running ad hoc commands, that is commands executed in realtime by an administrator working at the terminal, using the ansible command.
2. Running playbooks, YAML documents containing tasks each of which are equivalent to a single ad hoc command, using the ansible-playbook command. Any ad hoc command can be rewritten as a playbook, but some modules can only be used effectively as playbooks.

Playbooks, in turn, can be written in two styles:

1. Using "k=v" syntax, where keys and values are defined inline

tasks:
  - name: Install htop
    dnf: name=htop state=latest

2. Using proper YAML syntax

tasks:
  - name: Install htop
    dnf:
      name: htop
      state: latest

Variable substitution

Variable substitution is done by specifying the name of the placeholder variable and its value under vars as a sibling to tasks and handlers ^{linuxjournal.com}

---
- hosts: webservers
  become: yes
  vars:
    package_name: apache2
  tasks:
    - name: this installs a package
      apt: "name={{ package_name }} update_cache=yes state=latest"
      notify: enable apache

  handlers:
    - name: enable apache
      service: "name={{ package_name }} enabled=yes state=started" 

Conditional logic

Conditional logic is implemented with each task by defining a condition as the value for a property when ^{linuxjournal.com}

---
- hosts: webservers
  become: yes
  tasks:
    - name: install apache this way
      apt: name=apache2 update_cache=yes state=latest
      notify: start apache2
      when: ansible_os_family == "Debian"

    - name: install apache that way
      yum: name=httpd state=latest
      notify: start httpd
      when: ansible_os_family == "RedHat"

  handlers:
    - name: start apache2
      service: name=apache2 enabled=yes state=started

    - name: start httpd
      service: name=httpd enabled=yes state=started