Ansible

Ansible is an automated configuration manager for controlling infrastructure. By using ansible we can divide our infrastructure (nodes) into groups and define tasks (roles) for them. Ansible is implemented with python and it works using ssh.

Ansible is module based, meaning that it has plugins and modules in order to define your tasks. Also, you can use the shell feature of ansible to write your own manifests. However, the modules are implemented in a better way, in case of errors and edge cases.

structure

Ansible structure consists of inventory, roles, logs, playbooks and an ansible config file. In the next part we are going to dive into each of these sections.

inventory

Each ansible template has a hosts.ini (or hosts.yaml) file that contains information about our hosts for grouping them.

[all:children]
web
db

[web]
host2

[db]
host1

We put them in a directory called inventory. We can group our hosts by using the following structure:

|_ inventory
  |_ region-e
    |_ hosts-dc1.ini
    |_ hosts-dc2.ini
  |_ region-w
    |_ hosts-dc3.ini

playbooks

For executing tasks on each group, we assign some roles to each group. We need to create playbooks in order to perform such operation. A playbook looks like this:

---
- name: web
  hosts: web
  roles:
    - app
    - nginx

We can also import playbooks in another playbook:

---
- import_playbook: default.yml

vars

In order to create our variables to use them in other files, we have group_vars and host_vars. In group_vars we set variables for hosts groups, and in host_vars we set variables for hosts. We also have a vars directory for general variables.

|_ group_vars
  |_ web.yml
|_ host_vars
  |_ host1.yml
|_ vars

roles

In this directory we create the tasks that we want to execute during configuration. For each operation we create a directory. In each directory we have a structure like this:

|_ roles
  |_ nginx
    |_ defaults (setting default variables)
      |_ main.yml
    |_ files (static config files)
    |_ handlers (triggering systemd commands)
      |_ main.yml
    |_ tasks (operations)
      |_ main.yml
    |_ templates (dynamic config files)
      |_ main.yml
    |_ vars
      |_ main.yml

Each role has a defaults directory for its own variables. It has files and templates for config files. It has a tasks directory for defining the tasks the are need to be done over a playbook.