Roles

• Role Directory Structure
• Using Roles
• Role Duplication and Execution
• Role Default Variables
• Role Dependencies
• Embedding Modules and Plugins In Roles
• Role Search Path
• Ansible Galaxy

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.
• defaults - default variables for the role (see Variables for more information).
• vars - other variables for the role (see Variables for more information).
• 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/example/tasks/main.yml
- name: added in 2.4, previouslly you used 'include'
  import_tasks: redhat.yml
  when: ansible_os_platform|lower == 'redhat'
- import_tasks: debian.yml
  when: ansible_os_platform|lower == 'debian'

# roles/example/tasks/redhat.yml
- yum:
    name: "httpd"
    state: present

# roles/example/tasks/debian.yml
- apt:
    name: "apache2"
    state: present

Roles may also include modules and other plugin types. For more information, please refer to the Embedding Modules and Plugins In Roles section below.

Using Roles

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:

• Any pre_tasks defined in the play.
• Any handlers triggered so far will be run.
• 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.
• Any tasks defined in the play.
• Any handlers triggered so far will be run.
• Any post_tasks defined in the play.
• Any handlers triggered so far will be run.

As of Ansible 2.4, you can now use roles inline with any other tasks using import_role or include_role:

---

- hosts: webservers
  tasks:
  - debug:
      msg: "before we run our role"
  - import_role:
      name: example
  - include_role:
      name: example
  - debug:
      msg: "after we ran our role"

When roles are defined in the classic manner, they are treated as static imports and processed during playbook parsing.

The name used for the role can be a simple name (see Role Search Path below), or it can be a fully qualified path:

---

- hosts: webservers
  roles:
    - { role: '/path/to/my/roles/common' }

Roles can accept parameters:

---

- hosts: webservers
  roles:
    - common
    - { role: foo_app_instance, dir: '/opt/a', app_port: 5000 }
    - { role: foo_app_instance, dir: '/opt/b', app_port: 5001 }

Or, using the newer syntax:

---

- hosts: webservers
  tasks:
  - include_role:
       name: foo_app_instance
    vars:
      dir: '/opt/a'
      app_port: 5000
  ...

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:

---

- hosts: webservers
  tasks:
  - include_role:
      name: some_role
    when: "ansible_os_family == 'RedHat'"

Finally, you may wish to assign tags to the roles you specify. You can do so inline:

---

- hosts: webservers
  roles:
    - { role: foo, tags: ["bar", "baz"] }

Or, again, using the newer syntax:

---

- hosts: webservers
  tasks:
  - import_role:
      name: foo
    tags:
    - bar
    - baz

Role Duplication and Execution

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:

---
- hosts: webservers
  roles:
  - foo
  - foo

Given the above, the role foo will only be run once.

To make roles run more than once, there are two options:

1. Pass different parameters in each role definition.
2. Add allow_duplicates: true to the meta/main.yml file for the role.

Example 1 - passing different parameters:

---
- hosts: webservers
  roles:
  - { role: foo, message: "first" }
  - { role: foo, message: "second" }

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

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

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:

---
dependencies:
  - { role: common, some_parameter: 3 }
  - { role: apache, apache_port: 80 }
  - { role: postgres, dbname: blarg, other_parameter: 12 }

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.

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.

Embedding Modules and Plugins In Roles

This is an advanced topic that should not be relevant for most users.

If you write a custom module (see Developing Modules) or a plugin (see 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’

Role Search Path

Ansible will search for roles in the following way:

• A roles/ directory, relative to the playbook file.
• By default, in /etc/ansible/roles

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 Configuration file for details about how to set this up in ansible.cfg.

Ansible Galaxy

Ansible Galaxy 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.