ansible.md

Abstractly speaking, Ansible is an utility for management of remote (and local ones too, though that sounds boring) PC instances. I personally have used it for managing VMs under vCenter, but the Ansible objective is far more broad. It's useful to see what it does and how.

First you have a task. It may be commands to run, or something special such as connecting to vCenter and powering off a VM. Tasks seems to always be described through means of a plugin/module, which is written in python.

Ansible just executes the task.

You may not trust the plugin, in this case you may set up a host with ssh connection on which you'd like to execute the task. Ansible requires setting the variable hosts:, which describes the host on which you want this to be executed (usually it's localhost though). How it works: Ansible connects to the host with ssh (unless it's localhost), and copies the plugin code there along with a small wrapper. Then executes it.

Tasks may be described as a "playbook" or "ad-hoc commands" (read as "a playbook written on the command line to ansible executable").

Misc

• Plugins and Modules are different things.
• Authentication involves writing a config which is parsed by a plugin. E.g. managing vSphere/vCenter involves writing a myconfig.yaml file with host addresses to connect, etc; the format is usually the same between all plugins, but it seems it may differ. Example of such plugin:

  - hosts: localhost
    connection: local
    tasks:
      - vmware_guest_powerstate:
          hostname: "vcenter-host"
          username: "my-user"
          password: "********"
          validate_certs: no
          name: "vm name"
          state: powered-on
        register: deploy
  

• listing available VMs: ansible-inventory --list -i myconfig.yaml

Plugins

Installation involves putting into a special directory. An example ~/.ansible/plugins/inventory/vmware_vm_inventory.py. To get the actual directories list where a plugin being looked up use ansible-doc -t <plugin_type> foo, for example ansible-doc -t inventory foo. The idea is that the command gonna fail because sure you don't have a plugin foo, and then it gonna print the directories.

Ad-hoc commands

Supposedly, you can run ansible from command line by writing down stuff you'd otherwise put in a playbook. Though for me the examples I used from the official docs were throwing errors. I deemed it wasn't worth putting further efforts.

Playbook

A configuration file used to execute commands/actions against VMs. Use with ansible-playbook command.

Running a single task

It's possible by providing a tags: field on tasks, and then exploiting --tags= option of ansible-playbook, but it doesn't look like a mature feature because if the tag did not match anything, there will be no errors. I had to work this around by splitting a playbook to multiple smaller ones, so I could run everything in it explicitly, without any tags.