The patterns document is now it's own chapter since it applies to playbooks and /usr/bin/ansible alike.
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Michael DeHaan
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.. _patterns:
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Inventory & Patterns
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====================
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Patterns
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++++++++
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Ansible works against multiple systems in your infrastructure at the
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same time. It does this by selecting portions of systems listed in
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Ansible's inventory file, which defaults to /etc/ansible/hosts.
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Patterns in Ansible are how we decide which hosts to manage. This can mean what hosts to communicate with, but in terms
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of :doc:`playbooks` it actually means what hosts to apply a particular configuration or IT process to.
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.. contents::
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:depth: 2
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.. _inventoryformat:
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Hosts and Groups
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++++++++++++++++
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The format for /etc/ansible/hosts is an INI format and looks like this::
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mail.example.com
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[webservers]
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foo.example.com
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bar.example.com
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[dbservers]
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one.example.com
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two.example.com
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three.example.com
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The things in brackets are group names. You don't have to have them,
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but they are useful.
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If you have hosts that run on non-standard SSH ports you can put the port number
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after the hostname with a colon. Ports listed in any SSH config file won't be read,
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so it is important that you set them if things are not running on the default port::
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badwolf.example.com:5309
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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::
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jumper ansible_ssh_port=5555 ansible_ssh_host=192.168.1.50
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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.
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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::
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[webservers]
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www[01:50].example.com
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In 1.0 and later, you can also do this for alphabetic ranges::
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[databases]
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db-[a:f].example.com
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For numeric patterns, leading zeros can be included or removed, as desired. Ranges are inclusive.
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In 1.1 and later, you can also select the connection type and user on a per host basis::
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[targets]
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localhost ansible_connection=local
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other1.example.com ansible_connection=ssh ansible_ssh_user=mpdehaan
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other2.example.com ansible_connection=ssh ansible_ssh_user=mdehaan
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All of these variables can of course also be set outside of the inventory file, in 'host_vars' if you wish
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to keep your inventory file simple.
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List of Reserved Inventory Parameters
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+++++++++++++++++++++++++++++++++++++
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As a summary, you can set these parameters as host inventory variables. (Some we have already
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mentioned).
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ansible_ssh_host
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The name of the host to connect to, if different from the alias you wish to give to it.
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ansible_ssh_port
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The ssh port number, if not 22
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ansible_ssh_user
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The default ssh user name to use.
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ansible_ssh_pass
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The ssh password to use (this is insecure, we strongly recommend using --ask-pass or SSH keys)
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ansible_connection
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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.
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ansible_ssh_private_key_file
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Private key file used by ssh. Useful if using multiple keys and you don't want to use SSH agent.
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ansible_syslog_facility
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The syslog facility to log to.
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ansible_python_interpreter
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The target host python path. This is userful for systems with more
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than one Python or not located at "/usr/bin/python" such as \*BSD, or where /usr/bin/python
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is not a 2.X series Python.
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ansible\_\*\_interpreter
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Works for anything such as ruby or perl and works just like ansible_python_interpreter.
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This replaces shebang of modules which will run on that host.
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Examples from a host file::
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some_host ansible_ssh_port=2222 ansible_ssh_user=manager
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aws_host ansible_ssh_private_key_file=/home/example/.ssh/aws.pem
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freebsd_host ansible_python_interpreter=/usr/local/bin/python
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ruby_module_host ansible_ruby_interpreter=/usr/bin/ruby.1.9.3
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Selecting Targets
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+++++++++++++++++
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We'll go over how to use the command line in :doc:`examples` section, however, basically it looks like this::
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We'll go over how to use the command line in :doc:`intro_examples` section, however, basically it looks like this::
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ansible <pattern_goes_here> -m <module_name> -a <arguments>
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@ -114,12 +14,10 @@ Such as::
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ansible webservers -m service -a "name=httpd state=restarted"
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Within :doc:`playbooks`, these patterns can be used for even greater purposes.
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Anyway, to use Ansible, you'll first need to know how to tell Ansible which hosts in your inventory file to talk to.
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Anyway, to use Ansible, you'll first need to know how to tell Ansible which hosts in your inventory to talk to.
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This is done by designating particular host names or groups of hosts.
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The following patterns target all hosts in the inventory file::
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The following patterns target all hosts in the inventory::
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all
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*
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@ -131,29 +29,34 @@ Basically 'all' is an alias for '*'. It is also possible to address a specific
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192.168.1.50
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192.168.1.*
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The following patterns address one or more groups, which are denoted
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with the aforementioned bracket headers in the inventory file::
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The following patterns address one or more groups. Groups seperated by a colon indicate an "OR" configuration.
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This means the host may be in either one group or the other::
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webservers
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webservers:dbservers
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You can exclude groups as well, for instance, all webservers not in Phoenix::
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You can exclude groups as well, for instance, all machines must be in the group webservers but not in the group phoenix::
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webservers:!phoenix
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You can also specify the intersection of two groups::
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You can also specify the intersection of two groups. This would mean the hosts must be in the group webservers and
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the host must also be in the group staging::
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webservers:&staging
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You can do combinations::
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webservers:dbservers:!phoenix:&staging
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webservers:dbservers:&staging:!phoenix
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You can also use variables::
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The above configuration means "all machines in the groups 'webservers' and 'dbservers' are to be managed if they are in
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the group 'staging' also, but the machines are not to be managed if they are in the group 'phoenix' ... whew!
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You can also use variables if you want to pass some group specifiers via the "-e" argument to ansible-playbook, but this
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is uncommonly used::
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webservers:!{{excluded}}:&{{required}}
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Individual host names, IPs and groups, can also be referenced using
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You also don't have to manage by strictly defined groups. Individual host names, IPs and groups, can also be referenced using
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wildcards::
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*.example.com
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@ -167,110 +70,15 @@ And if the pattern starts with a '~' it is treated as a regular expression::
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~(web|db).*\.example\.com
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Easy enough. See :doc:`examples` and then :doc:`playbooks` for how to do things to selected hosts.
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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.
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Host Variables
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++++++++++++++
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ansible-playbook site.yml --limit datacenter2
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It is easy to assign variables to hosts that will be used later in playbooks::
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[atlanta]
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host1 http_port=80 maxRequestsPerChild=808
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host2 http_port=303 maxRequestsPerChild=909
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Group Variables
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+++++++++++++++
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Variables can also be applied to an entire group at once::
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[atlanta]
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host1
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host2
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[atlanta:vars]
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ntp_server=ntp.atlanta.example.com
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proxy=proxy.atlanta.example.com
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Groups of Groups, and Group Variables
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+++++++++++++++++++++++++++++++++++++
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It is also possible to make groups of groups and assign
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variables to groups. These variables can be used by /usr/bin/ansible-playbook, but not
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/usr/bin/ansible::
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[atlanta]
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host1
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host2
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[raleigh]
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host2
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host3
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[southeast:children]
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atlanta
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raleigh
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[southeast:vars]
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some_server=foo.southeast.example.com
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halon_system_timeout=30
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self_destruct_countdown=60
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escape_pods=2
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[usa:children]
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southeast
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northeast
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southwest
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southeast
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If you need to store lists or hash data, or prefer to keep host and group specific variables
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separate from the inventory file, see the next section.
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Splitting Out Host and Group Specific Data
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++++++++++++++++++++++++++++++++++++++++++
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.. versionadded:: 0.6
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In addition to the storing variables directly in the INI file, host
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and group variables can be stored in individual files relative to the
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inventory file. These variable files are in YAML format.
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Assuming the inventory file path is::
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/etc/ansible/hosts
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If the host is named 'foosball', and in groups 'raleigh' and 'webservers', variables
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in YAML files at the following locations will be made available to the host::
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/etc/ansible/group_vars/raleigh
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/etc/ansible/group_vars/webservers
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/etc/ansible/host_vars/foosball
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For instance, suppose you have hosts grouped by datacenter, and each datacenter
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uses some different servers. The data in the groupfile '/etc/ansible/group_vars/raleigh' for
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the 'raleigh' group might look like::
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---
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ntp_server: acme.example.org
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database_server: storage.example.org
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It is ok if these files do not exist, this is an optional feature.
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Tip: In Ansible 1.2 or later the group_vars/ and host_vars/ directories can exist in either
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the playbook directory OR the inventory directory. If both paths exist, variables in the playbook
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directory will be loaded second.
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Tip: Keeping your inventory file and variables in a git repo (or other version control)
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is an excellent way to track changes to your inventory and host variables.
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.. versionadded:: 0.5
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If you ever have two python interpreters on a system, or your Python version 2 interpreter is not found
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at /usr/bin/python, set an inventory variable called 'ansible_python_interpreter' to the Python
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interpreter path you would like to use.
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Easy enough. See :doc:`intro_adhoc` and then :doc:`playbooks` for how to apply this knowledge.
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.. seealso::
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:doc:`examples`
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:doc:`intro_adhoc`
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Examples of basic commands
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:doc:`playbooks`
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Learning ansible's configuration management language
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