166 lines
6.1 KiB
ReStructuredText
166 lines
6.1 KiB
ReStructuredText
.. _lookup_plugins:
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Lookup Plugins
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==============
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.. contents::
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:local:
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:depth: 2
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Lookup plugins allow Ansible to access data from outside sources.
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This can include reading the filesystem in addition to contacting external datastores and services.
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Like all templating, these plugins are evaluated on the Ansible control machine, not on the target/remote.
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The data returned by a lookup plugin is made available using the standard templating system in Ansible,
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and are typically used to load variables or templates with information from those systems.
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Lookups are an Ansible-specific extension to the Jinja2 templating language.
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.. note::
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- Lookups are executed with a working directory relative to the role or play,
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as opposed to local tasks, which are executed relative the executed script.
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- Since Ansible version 1.9, you can pass wantlist=True to lookups to use in Jinja2 template "for" loops.
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- Lookup plugins are an advanced feature; to best leverage them you should have a good working knowledge of how to use Ansible plays.
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.. warning::
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- Some lookups pass arguments to a shell. When using variables from a remote/untrusted source, use the `|quote` filter to ensure safe usage.
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.. _enabling_lookup:
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Enabling lookup plugins
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-----------------------
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You can activate a custom lookup by either dropping it into a ``lookup_plugins`` directory adjacent to your play, inside a role, or by putting it in one of the lookup directory sources configured in :ref:`ansible.cfg <ansible_configuration_settings>`.
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.. _using_lookup:
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Using lookup plugins
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--------------------
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Lookup plugins can be used anywhere you can use templating in Ansible: in a play, in variables file, or in a Jinja2 template for the :ref:`template <template_module>` module.
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.. code-block:: yaml
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vars:
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file_contents: "{{lookup('file', 'path/to/file.txt')}}"
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Lookups are an integral part of loops. Wherever you see ``with_``, the part after the underscore is the name of a lookup.
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This is also the reason most lookups output lists and take lists as input; for example, ``with_items`` uses the :ref:`items <items_lookup>` lookup:
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.. code-block:: yaml
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tasks:
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- name: count to 3
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debug: msg={{item}}
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with_items: [1, 2, 3]
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You can combine lookups with :ref:`playbooks_filters`, :ref:`playbooks_tests` and even each other to do some complex data generation and manipulation. For example:
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.. code-block:: yaml
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tasks:
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- name: valid but useless and over complicated chained lookups and filters
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debug: msg="find the answer here:\n{{ lookup('url', 'https://google.com/search/?q=' + item|urlencode)|join(' ') }}"
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with_nested:
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- "{{lookup('consul_kv', 'bcs/' + lookup('file', '/the/question') + ', host=localhost, port=2000')|shuffle}}"
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- "{{lookup('sequence', 'end=42 start=2 step=2')|map('log', 4)|list)}}"
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- ['a', 'c', 'd', 'c']
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.. versionadded:: 2.6
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You can now control how errors behave in all lookup plugins by setting ``errors`` to ``ignore``, ``warn``, or ``strict``. The default setting is ``strict``, which causes the task to fail. For example:
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To ignore errors::
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- name: file doesnt exist, but i dont care .. file plugin itself warns anyways ...
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debug: msg="{{ lookup('file', '/idontexist', errors='ignore') }}"
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[WARNING]: Unable to find '/idontexist' in expected paths (use -vvvvv to see paths)
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ok: [localhost] => {
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"msg": ""
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}
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To get a warning instead of a failure::
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- name: file doesnt exist, let me know, but continue
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debug: msg="{{ lookup('file', '/idontexist', errors='warn') }}"
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[WARNING]: Unable to find '/idontexist' in expected paths (use -vvvvv to see paths)
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[WARNING]: An unhandled exception occurred while running the lookup plugin 'file'. Error was a <class 'ansible.errors.AnsibleError'>, original message: could not locate file in lookup: /idontexist
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ok: [localhost] => {
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"msg": ""
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}
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Fatal error (the default)::
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- name: file doesnt exist, FAIL (this is the default)
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debug: msg="{{ lookup('file', '/idontexist', errors='strict') }}"
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[WARNING]: Unable to find '/idontexist' in expected paths (use -vvvvv to see paths)
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fatal: [localhost]: FAILED! => {"msg": "An unhandled exception occurred while running the lookup plugin 'file'. Error was a <class 'ansible.errors.AnsibleError'>, original message: could not locate file in lookup: /idontexist"}
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.. _query:
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Invoking lookup plugins with ``query``
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--------------------------------------
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.. versionadded:: 2.5
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In Ansible 2.5, a new jinja2 function called ``query`` was added for invoking lookup plugins. The difference between ``lookup`` and ``query`` is largely that ``query`` will always return a list.
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The default behavior of ``lookup`` is to return a string of comma separated values. ``lookup`` can be explicitly configured to return a list using ``wantlist=True``.
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This was done primarily to provide an easier and more consistent interface for interacting with the new ``loop`` keyword, while maintaining backwards compatibility with other uses of ``lookup``.
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The following examples are equivalent::
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lookup('dict', dict_variable, wantlist=True)
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query('dict', dict_variable)
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As demonstrated above the behavior of ``wantlist=True`` is implicit when using ``query``.
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Additionally, ``q`` was introduced as a shortform of ``query``::
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q('dict', dict_variable)
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.. _lookup_plugins_list:
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Plugin list
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-----------
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You can use ``ansible-doc -t lookup -l`` to see the list of available plugins. Use ``ansible-doc -t lookup <plugin name>`` to see specific documents and examples.
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.. toctree:: :maxdepth: 1
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:glob:
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lookup/*
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.. seealso::
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:ref:`about_playbooks`
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An introduction to playbooks
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:ref:`inventory_plugins`
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Ansible inventory plugins
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:ref:`callback_plugins`
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Ansible callback plugins
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:ref:`playbooks_filters`
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Jinja2 filter plugins
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:ref:`playbooks_tests`
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Jinja2 test plugins
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:ref:`playbooks_lookups`
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Jinja2 lookup plugins
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`User Mailing List <https://groups.google.com/group/ansible-devel>`_
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Have a question? Stop by the google group!
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`irc.freenode.net <http://irc.freenode.net>`_
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#ansible IRC chat channel
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