Playbook Roles and Include Statements

• Introduction
• Task Include Files And Encouraging Reuse
• Dynamic versus Static Includes
• Roles
• Role Default Variables
• Role Dependencies
• Embedding Modules and Plugins In Roles
• Ansible Galaxy

Introduction

While it is possible to write a playbook in one very large file (and you might start out learning playbooks this way), eventually you’ll want to reuse files and start to organize things.

At a basic level, including task files allows you to break up bits of configuration policy into smaller files. Task includes pull in tasks from other files. Since handlers are tasks too, you can also include handler files from the ‘handler’ section.

See Playbooks if you need a review of these concepts.

Playbooks can also include plays from other playbook files. When that is done, the plays will be inserted into the playbook to form a longer list of plays.

When you start to think about it – tasks, handlers, variables, and so on – begin to form larger concepts. You start to think about modeling what something is, rather than how to make something look like something. It’s no longer “apply this handful of THINGS to these hosts”, you say “these hosts are dbservers” or “these hosts are webservers”. In programming, we might call that “encapsulating” how things work. For instance, you can drive a car without knowing how the engine works.

Roles in Ansible build on the idea of include files and combine them to form clean, reusable abstractions – they allow you to focus more on the big picture and only dive down into the details when needed.

We’ll start with understanding includes so roles make more sense, but our ultimate goal should be understanding roles – roles are great and you should use them every time you write playbooks.

See the ansible-examples repository on GitHub for lots of examples of all of this put together. You may wish to have this open in a separate tab as you dive in.

Task Include Files And Encouraging Reuse

Suppose you want to reuse lists of tasks between plays or playbooks. You can use include files to do this. Use of included task lists is a great way to define a role that system is going to fulfill. Remember, the goal of a play in a playbook is to map a group of systems into multiple roles. Let’s see what this looks like...

A task include file simply contains a flat list of tasks, like so:

---
# possibly saved as tasks/foo.yml

- name: placeholder foo
  command: /bin/foo

- name: placeholder bar
  command: /bin/bar

Include directives look like this, and can be mixed in with regular tasks in a playbook:

tasks:

  - include: tasks/foo.yml

You can also pass variables into includes. We call this a ‘parameterized include’.

For instance, to deploy to multiple wordpress instances, I could encapsulate all of my wordpress tasks in a single wordpress.yml file, and use it like so:

tasks:
  - include: wordpress.yml wp_user=timmy
  - include: wordpress.yml wp_user=alice
  - include: wordpress.yml wp_user=bob

Starting in 1.0, variables can also be passed to include files using an alternative syntax, which also supports structured variables:

tasks:

  - include: wordpress.yml
    vars:
        wp_user: timmy
        ssh_keys:
          - keys/one.txt
          - keys/two.txt

Using either syntax, variables passed in can then be used in the included files. We’ll cover them in Variables. You can reference them like this:

{{ wp_user }}

(In addition to the explicitly passed-in parameters, all variables from the vars section are also available for use here as well.)

Playbooks can include other playbooks too, but that’s mentioned in a later section.

Includes can also be used in the ‘handlers’ section, for instance, if you want to define how to restart apache, you only have to do that once for all of your playbooks. You might make a handlers.yml that looks like:

---
# this might be in a file like handlers/handlers.yml
- name: restart apache
  service: name=apache state=restarted

And in your main playbook file, just include it like so, at the bottom of a play:

handlers:
  - include: handlers/handlers.yml

You can mix in includes along with your regular non-included tasks and handlers.

Includes can also be used to import one playbook file into another. This allows you to define a top-level playbook that is composed of other playbooks.

For example:

- name: this is a play at the top level of a file
  hosts: all
  remote_user: root

  tasks:

  - name: say hi
    tags: foo
    shell: echo "hi..."

- include: load_balancers.yml
- include: webservers.yml
- include: dbservers.yml

Note that you cannot do variable substitution when including one playbook inside another.

Dynamic versus Static Includes

Ansible 2.0 changes how include tasks are processed. In previous versions of Ansible, includes acted as a pre-processor statement and were read during playbook parsing time. This created problems with things like inventory variables (like group and host vars, which are not available during the parsing time) were used in the included file name.

Ansible 2.0 instead makes includes “dynamic”, meaning they are not evaluated until the include task is reached during the play execution. This change allows the reintroduction of loops on include statements, such as the following:

- include: foo.yml param={{item}}
  with_items:
  - 1
  - 2
  - 3

It is also possible to use variables from any source with a dynamic include:

- include: "{{inventory_hostname}}.yml"

Dynamic includes introduced some other limitations due to the fact that the included file is not read in until that task is reached during the execution of the play. When using dynamic includes, it is important to keep these limitations in mind:

• You cannot use notify to trigger a handler name which comes from a dynamic include.
• You cannot use --start-at-task to begin execution at a task inside a dynamic include.
• Tags which only exist inside a dynamic include will not show up in –list-tags output.
• Tasks which only exist inside a dynamic include will not show up in –list-tasks output.

To work around these limitations, Ansible 2.1 introduces the static option for includes:

- include: foo.yml
  static: <yes|no|true|false>

By default in Ansible 2.1 and higher, includes are automatically treated as static rather than dynamic when the include meets the following conditions:

• The include does not use any loops
• The included file name does not use any variables
• The static option is not explicitly disabled (ie. static: no)
• The ansible.cfg options to force static includes (see below) are disabled

Two options are available in the ansible.cfg configuration for static includes:

• task_includes_static - forces all includes in tasks sections to be static.
• handler_includes_static - forces all includes in handlers sections to be static.

These options allow users to force playbooks to behave exactly as they did in 1.9.x and before.

Roles

Now that you have learned about tasks and handlers, what is the best way to organize your playbooks? The short answer is to use roles! 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.

Roles are just automation around ‘include’ directives as described above, and really don’t contain much additional magic beyond some improvements to search path handling for referenced files. However, that can be a big thing!

Example project structure:

site.yml
webservers.yml
fooservers.yml
roles/
   common/
     files/
     templates/
     tasks/
     handlers/
     vars/
     defaults/
     meta/
   webservers/
     files/
     templates/
     tasks/
     handlers/
     vars/
     defaults/
     meta/

In a playbook, it would look like this:

---
- 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

In Ansible 1.4 and later you can configure a 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.

If any files are not present, they are just ignored. So it’s ok to not have a ‘vars/’ subdirectory for the role, for instance.

Note, you are still allowed to list tasks, vars_files, and handlers “loose” in playbooks without using roles, but roles are a good organizational feature and are highly recommended. If there are loose things in the playbook, the roles are evaluated first.

Also, should you wish to parameterize roles, by adding variables, you can do so, like this:

---

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

While it’s probably not something you should do often, you can also conditionally apply roles like so:

---

- hosts: webservers
  roles:
    - { role: some_role, when: "ansible_os_family == 'RedHat'" }

This works by applying the conditional to every task in the role. Conditionals are covered later on in the documentation.

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"] }

Note that this tags all of the tasks in that role with the tags specified, overriding any tags that are specified inside the role. 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.

If the play still has a ‘tasks’ section, those tasks are executed after roles are applied.

If you want to define certain tasks to happen before AND after roles are applied, you can do this:

---

- hosts: webservers

  pre_tasks:
    - shell: echo 'hello'

  roles:
    - { role: some_role }

  tasks:
    - shell: echo 'still busy'

  post_tasks:
    - shell: echo 'goodbye'

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. 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 can also be specified as a full path, just like top level roles:

---
dependencies:
   - { role: '/path/to/common/roles/foo', x: 1 }

Role dependencies can also be installed from source control repos or tar files (via galaxy) using comma separated format of path, an optional version (tag, commit, branch etc) and optional friendly role name (an attempt is made to derive a role name from the repo name or archive filename). Both through the command line or via a requirements.yml passed to ansible-galaxy.

Roles dependencies are always executed before the role that includes them, and are recursive. By default, roles can also only be added as a dependency once - if another role also lists it as a dependency it will not be run again. This behavior can be overridden by adding allow_duplicates: yes to the meta/main.yml file. For example, a role named ‘car’ could add a role named ‘wheel’ to its dependencies as follows:

---
dependencies:
- { role: wheel, n: 1 }
- { role: wheel, n: 2 }
- { role: wheel, n: 3 }
- { role: wheel, n: 4 }

And the meta/main.yml for wheel contained the following:

---
allow_duplicates: yes
dependencies:
- { role: tire }
- { role: brake }

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

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’

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.