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ansible/docsite/latest/rst/api.rst
Michael DeHaan bcaa983c2f Document inventory script upgrades
2013-08-04 11:45:31 -04:00

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API & Integrations
==================
There are several interesting ways to use Ansible from an API perspective. You can use
the Ansible python API to control nodes, you can extend Ansible to respond to various python events,
and you can plug in inventory data from external data sources. Ansible is written in its own
API so you have a considerable amount of power across the board.
.. contents:: `Table of contents`
:depth: 2
Python API
----------
The Python API is very powerful, and is how the ansible CLI and ansible-playbook
are implemented.
It's pretty simple::
import ansible.runner
runner = ansible.runner.Runner(
module_name='ping',
module_args='',
pattern='web*',
forks=10
)
datastructure = runner.run()
The run method returns results per host, grouped by whether they
could be contacted or not. Return types are module specific, as
expressed in the 'ansible-modules' documentation.::
{
"dark" : {
"web1.example.com" : "failure message"
},
"contacted" : {
"web2.example.com" : 1
}
}
A module can return any type of JSON data it wants, so Ansible can
be used as a framework to rapidly build powerful applications and scripts.
Detailed API Example
````````````````````
The following script prints out the uptime information for all hosts::
#!/usr/bin/python
import ansible.runner
import sys
# construct the ansible runner and execute on all hosts
results = ansible.runner.Runner(
pattern='*', forks=10,
module_name='command', module_args='/usr/bin/uptime',
).run()
if results is None:
print "No hosts found"
sys.exit(1)
print "UP ***********"
for (hostname, result) in results['contacted'].items():
if not 'failed' in result:
print "%s >>> %s" % (hostname, result['stdout'])
print "FAILED *******"
for (hostname, result) in results['contacted'].items():
if 'failed' in result:
print "%s >>> %s" % (hostname, result['msg'])
print "DOWN *********"
for (hostname, result) in results['dark'].items():
print "%s >>> %s" % (hostname, result)
Advanced programmers may also wish to read the source to ansible itself, for
it uses the Runner() API (with all available options) to implement the
command line tools ``ansible`` and ``ansible-playbook``.
Plugins Available Online
------------------------
The remainder of features in the API docs have components available in `ansible-plugins <https://github.com/ansible/ansible/blob/devel/plugins>`_. Send us a github pull request if you develop any interesting features.
External Inventory Scripts
--------------------------
Often a user of a configuration management system will want to keep inventory
in a different system. Frequent examples include LDAP, `Cobbler <http://cobbler.github.com>`_,
or a piece of expensive enterprisey CMDB software. Ansible easily supports all
of these options via an external inventory system. The plugins directory contains some of these already -- including options for EC2/Eucalyptus and OpenStack, which will be detailed below.
It's possible to write an external inventory script in any language. If you are familiar with Puppet terminology, this concept is basically the same as 'external nodes', with the slight difference that it also defines which hosts are managed.
Script Conventions
``````````````````
When the external node script is called with the single argument '--list', the script must return a JSON hash/dictionary of all the groups to be managed.
Each group's value should be either a hash/dictionary containing a list of each host/IP, potential child groups, and potential group variables, or
simply a list of host/IP addresses, like so::
{
"databases" : {
"hosts" : [ "host1.example.com", "host2.example.com" ],
"vars" : {
"a" : true
}
},
"webservers" : [ "host2.example.com", "host3.example.com" ],
"atlanta" : {
"hosts" : [ "host1.example.com", "host4.example.com", "host5.example.com" ],
"vars" : {
"b" : false
},
"children": [ "marietta", "5points" ],
},
"marietta" : [ "host6.example.com" ],
"5points" : [ "host7.example.com" ]
}
.. versionadded: 1.0
Before version 1.0, each group could only have a list of hostnames/IP addresses, like the webservers, marietta, and 5points groups above.
When called with the arguments '--host <hostname>' (where <hostname> is a host from above), the script must return either an empty JSON
hash/dictionary, or a hash/dictionary of variables to make available to templates and playbooks. Returning variables is optional,
if the script does not wish to do this, returning an empty hash/dictionary is the way to go::
{
"favcolor" : "red",
"ntpserver" : "wolf.example.com",
"monitoring" : "pack.example.com"
}
Tuning the External Inventory Script
````````````````````````````````````
.. versionadded: 1.3
The stock inventory script system detailed above works for all versions of Ansible, but calling
'--host' for every host can be rather expensive, especially if it involves expensive API calls to
a remote subsystemm. In Ansible
1.3 or later, if the inventory script returns a top level element called "_meta", it is possible
to return all of the host variables in one inventory script call. When this meta element contains
a value for "hostvars", the inventory script will not be invoked with "--host" for each host. This
results in a significant performance increase for large numbers of hosts, and also makes client
side caching easier to implement for the inventory script.
The data to be added to the top level JSON dictionary looks like this::
{
# results of inventory script as above go here
# ...
"_meta" : {
"hostvars" : {
"moocow.example.com" : { "asdf" : 1234 },
"llama.example.com" : { "asdf" : 5678 },
}
}
}
Example: The Cobbler External Inventory Script
``````````````````````````````````````````````
It is expected that many Ansible users will also be `Cobbler <http://cobbler.github.com>`_ users. Cobbler has a generic
layer that allows it to represent data for multiple configuration management systems (even at the same time), and has
been referred to as a 'lightweight CMDB' by some admins. This particular script will communicate with Cobbler
using Cobbler's XMLRPC API.
To tie Ansible's inventory to Cobbler (optional), copy `this script <https://raw.github.com/ansible/ansible/devel/plugins/inventory/cobbler.py>`_ to /etc/ansible/hosts and `chmod +x` the file. cobblerd will now need
to be running when you are using Ansible.
Test the file by running `./etc/ansible/hosts` directly. You should see some JSON data output, but it may not have
anything in it just yet.
Let's explore what this does. In cobbler, assume a scenario somewhat like the following::
cobbler profile add --name=webserver --distro=CentOS6-x86_64
cobbler profile edit --name=webserver --mgmt-classes="webserver" --ksmeta="a=2 b=3"
cobbler system edit --name=foo --dns-name="foo.example.com" --mgmt-classes="atlanta" --ksmeta="c=4"
cobbler system edit --name=bar --dns-name="bar.example.com" --mgmt-classes="atlanta" --ksmeta="c=5"
In the example above, the system 'foo.example.com' will be addressable by ansible directly, but will also be addressable when using the group names 'webserver' or 'atlanta'. Since Ansible uses SSH, we'll try to contract system foo over 'foo.example.com', only, never just 'foo'. Similarly, if you try "ansible foo" it wouldn't find the system... but "ansible 'foo*'" would, because the system DNS name starts with 'foo'.
The script doesn't just provide host and group info. In addition, as a bonus, when the 'setup' module is run (which happens automatically when using playbooks), the variables 'a', 'b', and 'c' will all be auto-populated in the templates::
# file: /srv/motd.j2
Welcome, I am templated with a value of a={{ a }}, b={{ b }}, and c={{ c }}
Which could be executed just like this::
ansible webserver -m setup
ansible webserver -m template -a "src=/tmp/motd.j2 dest=/etc/motd"
.. note::
The name 'webserver' came from cobbler, as did the variables for
the config file. You can still pass in your own variables like
normal in Ansible, but variables from the external inventory script
will override any that have the same name.
So, with the template above (motd.j2), this would result in the following data being written to /etc/motd for system 'foo'::
Welcome, I am templated with a value of a=2, b=3, and c=4
And on system 'bar' (bar.example.com)::
Welcome, I am templated with a value of a=2, b=3, and c=5
And technically, though there is no major good reason to do it, this also works too::
ansible webserver -m shell -a "echo {{ a }}"
So in other words, you can use those variables in arguments/actions as well. You might use this to name
a conf.d file appropriately or something similar. Who knows?
So that's the Cobbler integration support -- using the cobbler script as an example, it should be trivial to adapt Ansible to pull inventory, as well as variable information, from any data source. If you create anything interesting, please share with the mailing list, and we can keep it in the source code tree for others to use.
Example: AWS EC2 External Inventory Script
``````````````````````````````````````````
If you use Amazon Web Services EC2, maintaining an inventory file might not be the best approach. For this reason, you can use the `EC2 external inventory <https://raw.github.com/ansible/ansible/devel/plugins/inventory/ec2.py>`_ script.
You can use this script in one of two ways. The easiest is to use Ansible's ``-i`` command line option and specify the path to the script.
ansible -i ec2.py -u ubuntu us-east-1d -m ping
The second option is to copy the script to `/etc/ansible/hosts` and `chmod +x` it. You will also need to copy the `ec2.ini <https://raw.github.com/ansible/ansible/devel/plugins/inventory/ec2.ini>`_ file to `/etc/ansible/ec2.ini`. Then you can run ansible as you would normally.
To successfully make an API call to AWS, you will need to configure Boto (the Python interface to AWS). There are a `variety of methods <http://docs.pythonboto.org/en/latest/boto_config_tut.html>`_ available, but the simplest is just to export two environment variables:
export AWS_ACCESS_KEY_ID='AK123'
export AWS_SECRET_ACCESS_KEY='abc123'
You can test the script by itself to make sure your config is correct
cd plugins/inventory
./ec2.py --list
After a few moments, you should see your entire EC2 inventory across all regions in JSON.
Since each region requires its own API call, if you are only using a small set of regions, feel free to edit ``ec2.ini`` and list only the regions you are interested in. There are other config options in ``ec2.ini`` including cache control, and destination variables.
At their heart, inventory files are simply a mapping from some name to a destination address. The default ``ec2.ini`` settings are configured for running Ansible from outside EC2 (from your laptop for example). If you are running Ansible from within EC2, internal DNS names and IP addresses may make more sense than public DNS names. In this case, you can modify the ``destination_variable`` in ``ec2.ini`` to be the private DNS name of an instance. This is particularly important when running Ansible within a private subnet inside a VPC, where the only way to access an instance is via its private IP address. For VPC instances, `vpc_destination_variable` in ``ec2.ini`` provides a means of using which ever `boto.ec2.instance variable <http://docs.pythonboto.org/en/latest/ref/ec2.html#module-boto.ec2.instance>`_ makes the most sense for your use case.
The EC2 external inventory provides mappings to instances from several groups:
Instance ID
These are groups of one since instance IDs are unique.
e.g.
``i-00112233``
``i-a1b1c1d1``
Region
A group of all instances in an AWS region.
e.g.
``us-east-1``
``us-west-2``
Availability Zone
A group of all instances in an availability zone.
e.g.
``us-east-1a``
``us-east-1b``
Security Group
Instances belong to one or more security groups. A group is created for each security group, with all characters except alphanumerics, dashes (-) converted to underscores (_). Each group is prefixed by ``security_group_``
e.g.
``security_group_default``
``security_group_webservers``
``security_group_Pete_s_Fancy_Group``
Tags
Each instance can have a variety of key/value pairs associated with it called Tags. The most common tag key is 'Name', though anything is possible. Each key/value pair is its own group of instances, again with special characters converted to underscores, in the format ``tag_KEY_VALUE``
e.g.
``tag_Name_Web``
``tag_Name_redis-master-001``
``tag_aws_cloudformation_logical-id_WebServerGroup``
When the Ansible is interacting with a specific server, the EC2 inventory script is called again with the ``--host HOST`` option. This looks up the HOST in the index cache to get the instance ID, and then makes an API call to AWS to get information about that specific instance. It then makes information about that instance available as variables to your playbooks. Each variable is prefixed by ``ec2_``. Here are some of the variables available:
- ec2_architecture
- ec2_description
- ec2_dns_name
- ec2_id
- ec2_image_id
- ec2_instance_type
- ec2_ip_address
- ec2_kernel
- ec2_key_name
- ec2_launch_time
- ec2_monitored
- ec2_ownerId
- ec2_placement
- ec2_platform
- ec2_previous_state
- ec2_private_dns_name
- ec2_private_ip_address
- ec2_public_dns_name
- ec2_ramdisk
- ec2_region
- ec2_root_device_name
- ec2_root_device_type
- ec2_security_group_ids
- ec2_security_group_names
- ec2_spot_instance_request_id
- ec2_state
- ec2_state_code
- ec2_state_reason
- ec2_status
- ec2_subnet_id
- ec2_tag_Name
- ec2_tenancy
- ec2_virtualization_type
- ec2_vpc_id
Both ``ec2_security_group_ids`` and ``ec2_security_group_names`` are comma-separated lists of all security groups. Each EC2 tag is a variable in the format ``ec2_tag_KEY``.
To see the complete list of variables available for an instance, run the script by itself::
cd plugins/inventory
./ec2.py --host ec2-12-12-12-12.compute-1.amazonaws.com
Example: OpenStack Inventory Script
```````````````````````````````````
Though not detailed here in as much depth as the EC2 module, there's also a OpenStack Compute external inventory source in the plugins directory. It requires the Grizzly release of OpenStack or
later. See the inline comments in the module source for how to use it.
Callback Plugins
----------------
Ansible can be configured via code to respond to external events. This can include enhancing logging, signalling an external software
system, or even (yes, really) making sound effects. Some examples are contained in the plugins directory.
Connection Type Plugins
-----------------------
By default, ansible ships with a 'paramiko' SSH, native ssh (just called 'ssh'), and 'local' connection type, and an accelerated connection type named 'fireball'. All of these can be used
in playbooks and with /usr/bin/ansible to decide how you want to talk to remote machines. The basics of these connection types
are covered in the 'getting started' section. Should you want to extend Ansible to support other transports (SNMP? Message bus?
Carrier Pigeon?) it's as simple as copying the format of one of the existing modules and dropping it into the connection plugins
directory. The value of 'smart' for a connection allows selection of paramiko or openssh based on system capabilities, and chooses
'ssh' if OpenSSH supports ControlPersist, in Ansible 1.2.1 an later. Previous versions did not support 'smart'.
Lookup Plugins
--------------
Language constructs like "with_fileglob" and "with_items" are implemented via lookup plugins. Just like other plugin types, you can write your own.
Vars Plugins
------------
Playbook constructs like 'host_vars' and 'group_vars' work via 'vars' plugins. They inject additional variable
data into ansible runs that did not come from an inventory, playbook, or command line. Note that variables
can also be returned from inventory, so in most cases, you won't need to write or understand vars_plugins.
Filter Plugins
--------------
If you want more Jinja2 filters available in a Jinja2 template (filters like to_yaml and to_json are provided by default), they can be extended by writing a filter plugin.
Distributing Plugins
--------------------
.. versionadded: 0.8
Plugins are loaded from both Python's site_packages (those that ship with ansible) and a configured plugins directory, which defaults
to /usr/share/ansible/plugins, in a subfolder for each plugin type::
* action_plugins
* lookup_plugins
* callback_plugins
* connection_plugins
* filter_plugins
* vars_plugins
To change this path, edit the ansible configuration file.
In addition, plugins can be shipped in a subdirectory relative to a top-level playbook, in folders named the same as indicated above.
.. seealso::
:doc:`modules`
List of built-in modules
`Mailing List <http://groups.google.com/group/ansible-project>`_
Questions? Help? Ideas? Stop by the list on Google Groups
`irc.freenode.net <http://irc.freenode.net>`_
#ansible IRC chat channel
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