Ansible Tips and Tricks

updated: 12th of June 2019

published: 11th of June 2018

Overview

A collection of useful tips and tricks for Ansible which don't really justify a full blog post on their own. I'll keep updating this post when I come across something of value.

Callbacks

Convert the output of a playbook run to json. Either set the stdout_callback = json setting in the ansible.cfg or alternatively set the ANSIBLE_STDOUT_CALLBACK=json variable at the CLI on playbook execution.

    cmd
  
    ANSIBLE_STDOUT_CALLBACK=json ansible-playbook some-playbook.yml

Inventory

create an ad-hoc inventory using the -i or --inventory flags. An ad-hoc inventory allows you to run ansible or ansible-playbook against a node (or list of nodes) without creating an inventory file.

    cmd
  
    ansible-playbook -i myhost,<another-host> all -a 'uname -a'

Credit: https://gist.github.com/alces/f7e3de25d98a19550a4e4f97cabc2cf4

Roles

There is a fair bit of boilerplate involved in creating a role. There is an ansible-galaxy command to aid in the process of building a role. Optionaly add the --offline flag if the role is not intended for Ansible galaxy.

    cmd
  

    ansible-galaxy init role-name --offline

# output
- role-name was created successfully

# role-name directory contents
role-name/
├── defaults
│   └── main.yml
├── files
├── handlers
│   └── main.yml
├── meta
│   └── main.yml
├── README.md
├── tasks
│   └── main.yml
├── templates
├── tests
│   ├── inventory
│   └── test.yml
└── vars
    └── main.yml

8 directories, 8 files
  

Credit: https://docs.ansible.com/ansible/latest/reference_appendices/galaxy.html#create-roles

Variables

Get a json dict of all vars that will be applicable to a host at playbook runtime. The following command also shows you which groups a host belongs to and all groups that are available.

    cmd
  

    ansible -i inventory a.example.com -m debug -a "var=hostvars[inventory_hostname]"

# output
a.example.com | success >> {
    "var": {
        "hostvars": {
            "ansible_ssh_host": "10.0.0.1",
            "ansible_ssh_user": "user",
            "group_names": [
                "group1",
                "groups"
            ],
            "groups": {
                "all": [
                    "x.example.com",
                    "y.example.com",
                    "a.example.com",
                    "b.example.com"
                ],
                "group1": [
                    "a.example.com"
                ],
                "group2": [
                    "b.example.com"
                ],
                "groups": [
                    "a.example.com",
                    "b.example.com"
                ],
                "ungrouped": [
                    "x.example.com",
                    "y.example.com"
                ]
            },
            "inventory_hostname": "a.example.com",
            "inventory_hostname_short": "a"
        }
    }
}
  

Credit: https://unix.stackexchange.com/a/208854/294891

Find the source file that a variable was derived from. This is quite useful when you are using the Ansible variable precedence system to see which file a variable actually came from.

    cmd
  

    ansible -i inventory leaf01 -m debug -a "var=hostvars[inventory_hostname]['bgp']['asn']._data_source"

# output
leaf01 | SUCCESS => {
    "hostvars[inventory_hostname]['bgp']['asn']._data_source": "/path/to/host_vars/leaf01.yml"
}
  

Credit: https://twitter.com/codethenetwork/status/936733364089794560

# ansible