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.
Table of contents
The format for /etc/ansible/hosts is an INI format and 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.
If you have hosts that run on non-standard SSH ports you can put the port number after the hostname with a colon.
four.example.com:5309
In 0.6 and later, if you have a lot of hosts following similar patterns you can do this:
[webservers]
www[01-50].example.com
Leading zeros can be included or removed, as desired, and the ranges are inclusive.
We’ll go over how to use the command line in Command Line Examples And Next Steps section, however, basically it looks like this:
ansible <pattern_goes_here> -m <module_name> -a <arguments>
Such as:
ansible webservers -m service -a "name=httpd state=restarted"
Within Playbooks, these patterns can 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
You can exclude groups as well, for instance, all webservers not in Phoenix:
webservers:!phoenix
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
Easy enough. See Command Line Examples And Next Steps and then Playbooks for how to do things to selected hosts.
It is easy to assign variables to hosts that will be used later in playbooks:
[atlanta]
host1 http_port=80 maxRequestsPerChild=808
host2 http_port=303 maxRequestsPerChild=909
Variables can also be applied to an entire group at once:
[atlanta]
host1
host2
[atlanta:vars]
ntp_server=ntp.atlanta.example.com
proxy=proxy.atlanta.example.com
It is also possible to make groups of groups and assign variables to groups. These variables can be used by /usr/bin/ansible-playbook, but not /usr/bin/ansible:
[atlanta]
host1
host2
[raleigh]
host2
host3
[southeast:children]
atlanta
raleigh
[southeast:vars]
some_server=foo.southeast.example.com
halon_system_timeout=30
self_destruct_countdown=60
escape_pods=2
[usa:children]
southeast
northeast
southwest
southeast
If you need to store lists or hash data, or prefer to keep host and group specific variables seperate from the inventory file, see the next section.
New in version 0.6.
In addition to the storing variables directly in the INI file, host and group variables can be stored in individual files relative to the inventory file. These variable files are in YAML format.
Assuming the inventory file path is:
/etc/ansible/hosts
If the host is named ‘foosball’, and in groups ‘raleigh’ and ‘webservers’, variables in YAML files at the following locations will be made available to the host:
/etc/ansible/group_vars/raleigh
/etc/ansible/group_vars/webservers
/etc/ansible/host_vars/foosball
For instance, suppose you have hosts grouped by datacenter, and each datacenter uses some different servers. The data in the groupfile ‘/etc/ansible/group_vars/raleigh’ for the ‘raleigh’ group might look like:
---
ntp_server: acme.example.org
database_server: storage.example.org
It is ok if these files do not exist, this is an optional feature.
Tip: Keeping your inventory file and variables in a git repo (or other version control) is an excellent way to track changes to your inventory and host variables.
New in version 0.5: If you ever have two python interpreters on a system, set a variable called ‘ansible_python_interpreter’ to the Python interpreter path you would like to use.
Deprecated since version 0.7.
Ansible’s YAML inventory format is deprecated and will be removed in Ansible 0.7. Ansible 0.6 includes a conversion script.
Usage:
yaml_to_ini.py /etc/ansible/hosts
See also