Ansible works against multiple systems in your infrastructure at the same time. It does this by selecting portions of systems listed in Ansible’s inventory file, which defaults to /etc/ansible/hosts.
The format for /etc/ansible/hosts looks like this:
mail.example.com
[webservers]
foo.example.com
bar.example.com
[dbservers]
one.example.com
two.example.com
three.example.com
The things in brackets are group names, you don’t have to have them, but they are useful.
We’ll go over how to use the command line in Command Line Examples section, however, basically it looks like this:
ansible <pattern_goes_here> -m <module_name> -a <arguments>
Such as:
ansible <pattern_goes_here> -m service -a “name=httpd state=running”
Within Playbooks, these patterns can also be used, for even greater purposes.
Anyway, to use Ansible, you’ll first need to know how to tell Ansible which hosts in your inventory file to talk to. This is done by designating particular host names or groups of hosts.
The following patterns target all hosts in the inventory file:
all
*
Basically ‘all’ is an alias for ‘*’. It is also possible to address a specific host or hosts:
one.example.com
one.example.com:two.example.com
192.168.1.50
192.168.1.*
The following patterns address one or more groups, which are denoted with the aforementioned bracket headers in the inventory file:
webservers
webservers:dbservers
Individual host names (or IPs), but not groups, can also be referenced using wildcards:
*.example.com
*.com
It’s also ok to mix wildcard patterns and groups at the same time:
one*.com:dbservers
Note
It is not possible to target a host not in the inventory file. This is a safety feature.
Easy enough. Now see Command Line Examples and then Playbooks for how to do things to selected hosts.
See also