Roles are ways of automatically loading certain vars_files, tasks, and handlers based on a known file structure. Grouping content by roles also allows easy sharing of roles with other users.
Role Directory Structure
````````````````````````
Example project structure::
site.yml
webservers.yml
fooservers.yml
roles/
common/
tasks/
handlers/
files/
templates/
vars/
defaults/
meta/
webservers/
tasks/
defaults/
meta/
Roles expect files to be in certain directory names. Roles must include at least one of these directories, however it is perfectly fine to exclude any which are not being used. When in use, each directory must contain a ``main.yml`` file, which contains the relevant content:
-``tasks`` - contains the main list of tasks to be executed by the role.
-``handlers`` - contains handlers, which may be used by this role or even anywhere outside this role.
-``files`` - contains files which can be deployed via this role.
-``templates`` - contains templates which can be deployed via this role.
-``meta`` - defines some meta data for this role. See below for more details.
Other YAML files may be included in certain directories. For example, it is common practice to have platform-specific tasks included from the ``tasks/main.yml`` file::
Roles may also include modules and other plugin types. For more information, please refer to the :ref:`embedding_modules_and_plugins_in_roles` section below.
The classic (original) way to use roles is via the ``roles:`` option for a given play::
---
- hosts: webservers
roles:
- common
- webservers
This designates the following behaviors, for each role 'x':
- If roles/x/tasks/main.yml exists, tasks listed therein will be added to the play.
- If roles/x/handlers/main.yml exists, handlers listed therein will be added to the play.
- If roles/x/vars/main.yml exists, variables listed therein will be added to the play.
- If roles/x/defaults/main.yml exists, variables listed therein will be added to the play.
- If roles/x/meta/main.yml exists, any role dependencies listed therein will be added to the list of roles (1.3 and later).
- Any copy, script, template or include tasks (in the role) can reference files in roles/x/{files,templates,tasks}/ (dir depends on task) without having to path them relatively or absolutely.
When used in this manner, the order of execution for your playbook is as follows:
- Each role listed in ``roles`` will execute in turn. Any role dependencies defined in the roles ``meta/main.yml`` will be run first, subject to tag filtering and conditionals.
If using tags with tasks (described later as a means of only running part of a playbook), be sure to also tag your pre_tasks, post_tasks, and role dependencies and pass those along as well, especially if the pre/post tasks and role dependencies are used for monitoring outage window control or load balancing.
The ``include_role`` option was introduced in Ansible 2.3. The usage has changed slightly as of Ansible 2.4 to match the include (dynamic) vs. import (static) usage. See :ref:`dynamic_vs_static` for more details.
You can conditionally execute a role. This is not generally recommended with the classic syntax, but is common when using ``import_role`` or ``include_role``::
This *tags all of the tasks in that role with the tags specified*, appending to any tags that are specified inside the role. The tags in this example will *not* be added to tasks inside an ``include_role``. Tag the ``include_role`` task directly in order to apply tags to tasks in included roles. If you find yourself building a role with lots of tags and you want to call subsets of the role at different times, you should consider just splitting that role into multiple roles.
Ansible will only allow a role to execute once, even if defined multiple times, if the parameters defined on the role are not different for each definition. For example::
In this example, because each role definition has different parameters, ``foo`` will run twice.
Example 2 - using ``allow_duplicates: true``::
# playbook.yml
---
- hosts: webservers
roles:
- foo
- foo
# roles/foo/meta/main.yml
---
allow_duplicates: true
In this example, ``foo`` will run twice because we have explicitly enabled it to do so.
Role Default Variables
``````````````````````
..versionadded:: 1.3
Role default variables allow you to set default variables for included or dependent roles (see below). To create
defaults, simply add a ``defaults/main.yml`` file in your role directory. These variables will have the lowest priority
of any variables available, and can be easily overridden by any other variable, including inventory variables.
Role Dependencies
`````````````````
..versionadded:: 1.3
Role dependencies allow you to automatically pull in other roles when using a role. Role dependencies are stored in the ``meta/main.yml`` file contained within the role directory, as noted above. This file should contain a list of roles and parameters to insert before the specified role, such as the following in an example ``roles/myapp/meta/main.yml``::
Role dependencies must use the classic role definition style.
Role dependencies are always executed before the role that includes them, and may be recursive. Dependencies also follow the duplication rules specified above. If another role also lists it as a dependency, it will not be run again based on the same rules given above.
..note::
Always remember that when using ``allow_duplicates: true``, it needs to be in the dependent role's ``meta/main.yml``, not the parent.
For example, a role named ``car`` depends on a role named ``wheel`` as follows::
---
dependencies:
- { role: wheel, n: 1 }
- { role: wheel, n: 2 }
- { role: wheel, n: 3 }
- { role: wheel, n: 4 }
And the ``wheel`` role depends on two roles: ``tire`` and ``brake``. The ``meta/main.yml`` for wheel would then contain the following::
---
dependencies:
- { role: tire }
- { role: brake }
And the ``meta/main.yml`` for ``tire`` and ``brake`` would contain the following::
---
allow_duplicates: true
The resulting order of execution would be as follows::
tire(n=1)
brake(n=1)
wheel(n=1)
tire(n=2)
brake(n=2)
wheel(n=2)
...
car
Note that we did not have to use ``allow_duplicates: true`` for ``wheel``, because each instance defined by ``car`` uses different parameter values.
..note::
Variable inheritance and scope are detailed in the :doc:`playbooks_variables`.
If you write a custom module (see :ref:`developing_modules`) or a plugin (see :ref:`developing_plugins`), you may wish to distribute it as part of a role.
Generally speaking, Ansible as a project is very interested in taking high-quality modules into ansible core for inclusion, so this shouldn't be the norm, but it's quite easy to do.
A good example for this is if you worked at a company called AcmeWidgets, and wrote an internal module that helped configure your internal software, and you wanted other
people in your organization to easily use this module -- but you didn't want to tell everyone how to configure their Ansible library path.
Alongside the 'tasks' and 'handlers' structure of a role, add a directory named 'library'. In this 'library' directory, then include the module directly inside of it.
Assuming you had this::
roles/
my_custom_modules/
library/
module1
module2
The module will be usable in the role itself, as well as any roles that are called *after* this role, as follows::
- hosts: webservers
roles:
- my_custom_modules
- some_other_role_using_my_custom_modules
- yet_another_role_using_my_custom_modules
This can also be used, with some limitations, to modify modules in Ansible's core distribution, such as to use development versions of modules before they are released in production releases. This is not always advisable as API signatures may change in core components, however, and is not always guaranteed to work. It can be a handy way of carrying a patch against a core module, however, should you have good reason for this. Naturally the project prefers that contributions be directed back to github whenever possible via a pull request.
The same mechanism can be used to embed and distribute plugins in a role, using the same schema. For example, for a filter plugin::
roles/
my_custom_filter/
filter_plugins
filter1
filter2
They can then be used in a template or a jinja template in any role called after 'my_custom_filter'
In Ansible 1.4 and later you can configure an additional roles_path to search for roles. Use this to check all of your common roles out to one location, and share them easily between multiple playbook projects. See :ref:`intro_configuration` for details about how to set this up in ansible.cfg.
`Ansible Galaxy <https://galaxy.ansible.com>`_ is a free site for finding, downloading, rating, and reviewing all kinds of community developed Ansible roles and can be a great way to get a jumpstart on your automation projects.
You can sign up with social auth, and the download client 'ansible-galaxy' is included in Ansible 1.4.2 and later.
Read the "About" page on the Galaxy site for more information.
