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.
Patterns in Ansible are how we decide which hosts to manage. This can mean what hosts to communicate with, but in terms
of :doc:`playbooks` it actually means what hosts to apply a particular configuration or IT process to.
..contents::
:depth:2
.._inventoryformat:
Hosts and Groups
++++++++++++++++
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::
badwolf.example.com:5309
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::
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::
[webservers]
www[01:50].example.com
In 1.0 and later, you can also do this for alphabetic ranges::
[databases]
db-[a:f].example.com
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::
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.
List of Reserved Inventory Parameters
+++++++++++++++++++++++++++++++++++++
As a summary, you can set these parameters as host inventory variables. (Some we have already
mentioned).
ansible_ssh_host
The name of the host to connect to, if different from the alias you wish to give to it.
ansible_ssh_port
The ssh port number, if not 22
ansible_ssh_user
The default ssh user name to use.
ansible_ssh_pass
The ssh password to use (this is insecure, we strongly recommend using --ask-pass or SSH keys)
ansible_connection
Connection type of the host. Candidates are local, ssh or paramiko. The default is paramiko before Ansible 1.2, and 'smart' afterwards which detects whether usage of 'ssh' would be feasible based on whether ControlPersist is supported.
ansible_ssh_private_key_file
Private key file used by ssh. Useful if using multiple keys and you don't want to use SSH agent.
ansible_syslog_facility
The syslog facility to log to.
ansible_python_interpreter
The target host python path. This is userful for systems with more
than one Python or not located at "/usr/bin/python" such as \*BSD, or where /usr/bin/python
is not a 2.X series Python.
ansible\_\*\_interpreter
Works for anything such as ruby or perl and works just like ansible_python_interpreter.
This replaces shebang of modules which will run on that host.
We'll go over how to use the command line in :doc:`examples` section, however, basically it looks like this::
We'll go over how to use the command line in :doc:`intro_examples` section, however, basically it looks like this::
ansible <pattern_goes_here> -m <module_name> -a <arguments>
@ -114,12 +14,10 @@ Such as::
ansible webservers -m service -a "name=httpd state=restarted"
Within :doc:`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.
Anyway, to use Ansible, you'll first need to know how to tell Ansible which hosts in your inventory 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::
The following patterns target all hosts in the inventory::
all
*
@ -131,29 +29,34 @@ Basically 'all' is an alias for '*'. It is also possible to address a specific
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::
The following patterns address one or more groups. Groups seperated by a colon indicate an "OR" configuration.
This means the host may be in either one group or the other::
webservers
webservers:dbservers
You can exclude groups as well, for instance, all webservers not in Phoenix::
You can exclude groups as well, for instance, all machines must be in the group webservers but not in the group phoenix::
webservers:!phoenix
You can also specify the intersection of two groups::
You can also specify the intersection of two groups. This would mean the hosts must be in the group webservers and
the host must also be in the group staging::
webservers:&staging
You can do combinations::
webservers:dbservers:!phoenix:&staging
webservers:dbservers:&staging:!phoenix
You can also use variables::
The above configuration means "all machines in the groups 'webservers' and 'dbservers' are to be managed if they are in
the group 'staging' also, but the machines are not to be managed if they are in the group 'phoenix' ... whew!
You can also use variables if you want to pass some group specifiers via the "-e" argument to ansible-playbook, but this
is uncommonly used::
webservers:!{{excluded}}:&{{required}}
Individual host names, IPs and groups, can also be referenced using
You also don't have to manage by strictly defined groups. Individual host names, IPs and groups, can also be referenced using
wildcards::
*.example.com
@ -167,110 +70,15 @@ And if the pattern starts with a '~' it is treated as a regular expression::
~(web|db).*\.example\.com
Easy enough. See :doc:`examples` and then :doc:`playbooks` for how to do things to selected hosts.
Host Variables
++++++++++++++
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
Group Variables
+++++++++++++++
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
Groups of Groups, and Group Variables
+++++++++++++++++++++++++++++++++++++
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.
Splitting Out Host and Group Specific Data
++++++++++++++++++++++++++++++++++++++++++
..versionadded:: 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: In Ansible 1.2 or later the group_vars/ and host_vars/ directories can exist in either
the playbook directory OR the inventory directory. If both paths exist, variables in the playbook
directory will be loaded second.
While we're jumping a bit ahead, additionally, you can add an exclusion criteria just by supplying the "--limit" flag to /usr/bin/ansible or /usr/bin/ansible-playbook.
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.
ansible-playbook site.yml --limit datacenter2
..versionadded:: 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.
Easy enough. See :doc:`intro_adhoc` and then :doc:`playbooks` for how to apply this knowledge.
..seealso::
:doc:`examples`
:doc:`intro_adhoc`
Examples of basic commands
:doc:`playbooks`
Learning ansible's configuration management language
Michael DeHaan
11 years ago