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. Ports listed in any SSH config file won’t be read, so it is important that you set them if things are not running on the default port:
Suppose you have just static IPs and want to set up some aliases that don’t live in your host file, or you are connecting through tunnels. You can do things like this:
jumper ansible_ssh_port=5555 ansible_ssh_host=192.168.1.50
In the above example, trying to ansible against the host alias “jumper” (which may not even be a real hostname) will contact 192.168.1.50 on port 5555.
Adding a lot of hosts? In 0.6 and later, if you have a lot of hosts following similar patterns you can do this rather than listing each hostname:
In 1.0 and later, you can also do this for alphabetic ranges:
For numeric patterns, leading zeros can be included or removed, as desired. Ranges are inclusive.
In 1.1 and later, you can also select the connection type and user on a per host basis:
[targets] localhost ansible_connection=local other1.example.com ansible_connection=ssh ansible_ssh_user=mpdehaan other2.example.com ansible_connection=ssh ansible_ssh_user=mdehaan
All of these variables can of course also be set outside of the inventory file, in ‘host_vars’ if you wish to keep your inventory file simple.
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>
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:
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:
You can exclude groups as well, for instance, all webservers not in Phoenix:
You can also specify the intersection of two groups:
You can do combinations:
You can also use variables:
Individual host names, IPs and groups, can also be referenced using wildcards:
It’s also ok to mix wildcard patterns and groups at the same time:
And if the pattern starts with a ‘~’ it is treated as a regular expression:
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 separate 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:
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, or your Python version 2 interpreter is not found at /usr/bin/python, set an inventory variable called ‘ansible_python_interpreter’ to the Python interpreter path you would like to use.