Ansible ansible.builtin vs ansible.legacy: Collection Namespaces Explained

localhost ansible_connection=local

[defaults]
action_plugins = plugins/action

# Copyright 2012, Dag Wieers <dag@wieers.com>
# Copyright 2016, Toshio Kuratomi <tkuratomi@ansible.com>
#
# This file is part of Ansible
#
# Ansible is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# Ansible is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
from __future__ import (absolute_import, division, print_function)
__metaclass__ = type

from ansible.errors import AnsibleUndefinedVariable
from ansible.module_utils.six import string_types
from ansible.module_utils._text import to_text
from ansible.plugins.action import ActionBase

class ActionModule(ActionBase):
    ''' Print statements during execution '''

    TRANSFERS_FILES = False
    _VALID_ARGS = frozenset(('msg', 'var', 'verbosity'))

    def run(self, tmp=None, task_vars=None):
        if task_vars is None:
            task_vars = dict()

        validation_result, new_module_args = self.validate_argument_spec(
            argument_spec={
                'msg': {'type': 'raw', 'default': 'Hello world!'},
                'var': {'type': 'raw'},
                'verbosity': {'type': 'int', 'default': 0},
            },
            mutually_exclusive=(
                ('msg', 'var'),
            ),
        )

        result = super(ActionModule, self).run(tmp, task_vars)
        del tmp  # tmp no longer has any effect

        # get task verbosity
        verbosity = new_module_args['verbosity']

        if verbosity <= self._display.verbosity:
            if new_module_args['var']:
                try:
                    results = self._templar.template(new_module_args['var'], convert_bare=True, fail_on_undefined=True)
                    if results == new_module_args['var']:
                        # if results is not str/unicode type, raise an exception
                        if not isinstance(results, string_types):
                            raise AnsibleUndefinedVariable
                        # If var name is same as result, try to template it
                        results = self._templar.template("{{" + results + "}}", convert_bare=True, fail_on_undefined=True)
                except AnsibleUndefinedVariable as e:
                    results = u"VARIABLE IS NOT DEFINED!"
                    if self._display.verbosity > 0:
                        results += u": %s" % to_text(e)

                if isinstance(new_module_args['var'], (list, dict)):
                    # If var is a list or dict, use the type as key to display
                    result[to_text(type(new_module_args['var']))] = results
                else:
                    result[new_module_args['var']] = results
            else:
                result['msg'] = (new_module_args['msg'] + "foo")

            # force flag to make debug output module always verbose
            result['_ansible_verbose_always'] = True
        else:
            result['skipped_reason'] = "Verbosity threshold not met."
            result['skipped'] = True

        result['failed'] = False

        return result

---
- name: debug module Playbook
  hosts: all
  vars:
    fruit: "apple"
  tasks:
    - name: Builtin
      ansible.builtin.debug:
        msg: "{{ fruit }}"

$ ansible-playbook -i inventory ansible.builtin.yml

PLAY [debug module Playbook] ****************************************************************

TASK [Gathering Facts] ******************************************************************
ok: [localhost]

TASK [Builtin] **************************************************************************
ok: [localhost] => {
    "msg": "apple"
}

PLAY RECAP ******************************************************************************
localhost                  : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

---
- name: debug module Playbook
  hosts: all
  vars:
    fruit: "apple"
  tasks:
    - name: Legacy
      ansible.legacy.debug:
        msg: "{{ fruit }}"

$ ansible-playbook -i inventory ansible.legacy.yml 

PLAY [debug module Playbook] ****************************************************************

TASK [Gathering Facts] ******************************************************************
ok: [localhost]

TASK [Legacy] ***************************************************************************
ok: [localhost] => {
    "msg": "applefoo"
}

PLAY RECAP ******************************************************************************
localhost                  : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

---
- name: debug module Playbook
  hosts: all
  vars:
    fruit: "apple"
  tasks:
    - name: Vanilla
      debug:
        msg: "{{ fruit }}"

$ ansible-playbook -i inventory ansible.vanilla.yml 

PLAY [debug module Playbook] ****************************************************************

TASK [Gathering Facts] ******************************************************************
ok: [localhost]

TASK [Vanilla] **************************************************************************
ok: [localhost] => {
    "msg": "applefoo"
}

PLAY RECAP ******************************************************************************
localhost                  : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

# Short name (legacy, still works)
- copy:
    src: file.txt
    dest: /tmp/

# FQCN - builtin (recommended)
- ansible.builtin.copy:
    src: file.txt
    dest: /tmp/

# FQCN - legacy
- ansible.legacy.copy:
    src: file.txt
    dest: /tmp/

# Problem: "copy" could be YOUR custom module or the built-in
- copy:  # Which one?
    src: file.txt
    dest: /tmp/

# Solution: FQCN is explicit
- ansible.builtin.copy:  # Definitely the built-in
    src: file.txt
    dest: /tmp/

- myorg.tools.copy:  # Definitely your custom one
    src: file.txt
    dest: /tmp/

# Use ansible-lint to find short names
ansible-lint playbook.yml
# Rule: fqcn[action-core] - Use FQCN for builtin module actions

# Or find manually
grep -rn "^\s*- \(copy\|template\|file\|service\|apt\|yum\|debug\|command\|shell\|user\|group\):" roles/

- hosts: all
  tasks:
    - apt: name=nginx state=present
    - template: src=nginx.conf.j2 dest=/etc/nginx/nginx.conf
    - service: name=nginx state=started enabled=true
    - file: path=/var/www state=directory
    - copy: src=index.html dest=/var/www/index.html

- hosts: all
  tasks:
    - ansible.builtin.apt: name=nginx state=present
    - ansible.builtin.template: src=nginx.conf.j2 dest=/etc/nginx/nginx.conf
    - ansible.builtin.service: name=nginx state=started enabled=true
    - ansible.builtin.file: path=/var/www state=directory
    - ansible.builtin.copy: src=index.html dest=/var/www/index.html

# All these are ansible.builtin.*
ansible.builtin.apt
ansible.builtin.yum
ansible.builtin.dnf
ansible.builtin.copy
ansible.builtin.template
ansible.builtin.file
ansible.builtin.service
ansible.builtin.systemd
ansible.builtin.user
ansible.builtin.group
ansible.builtin.command
ansible.builtin.shell
ansible.builtin.debug
ansible.builtin.set_fact
ansible.builtin.assert
ansible.builtin.include_role
ansible.builtin.include_tasks
ansible.builtin.import_tasks
ansible.builtin.uri
ansible.builtin.get_url
ansible.builtin.unarchive
ansible.builtin.lineinfile
ansible.builtin.blockinfile
ansible.builtin.stat
ansible.builtin.setup
ansible.builtin.ping
ansible.builtin.raw
ansible.builtin.reboot
ansible.builtin.wait_for

# These need collection installation
community.general.timezone
community.general.ufw
community.docker.docker_container
amazon.aws.ec2_instance
ansible.posix.sysctl
ansible.windows.win_copy
community.mysql.mysql_db

# .ansible-lint
rules:
  fqcn:
    # Require FQCN for builtin modules
    - fqcn[action-core]
    # Require FQCN for all modules
    - fqcn[action]

# FQCN — recommended
- ansible.builtin.copy:
    src: file.txt
    dest: /tmp/file.txt

# Short name — still works but triggers lint warning
- copy:
    src: file.txt
    dest: /tmp/file.txt

fqcn[action-core]: Use FQCN for builtin module actions (copy).

# Fix: add ansible.builtin. prefix
- ansible.builtin.apt:
    name: nginx
- ansible.builtin.service:
    name: nginx
    state: started
- ansible.builtin.template:
    src: config.j2
    dest: /etc/config

# Community collections use their own namespace
- community.general.ufw:
    rule: allow
    port: 80

- community.docker.docker_container:
    name: web
    image: nginx

- amazon.aws.ec2_instance:
    instance_type: t3.micro

# Custom module in library/ directory
# library/my_custom_module.py

# Referenced as:
- my_custom_module:          # resolves via ansible.legacy
    param: value

# Or explicitly:
- ansible.legacy.my_custom_module:
    param: value

# Find all non-FQCN module usage
ansible-lint --profile moderate .

# Common replacements:
# copy → ansible.builtin.copy
# file → ansible.builtin.file
# apt → ansible.builtin.apt
# yum → ansible.builtin.yum
# service → ansible.builtin.service
# command → ansible.builtin.command
# shell → ansible.builtin.shell
# debug → ansible.builtin.debug
# template → ansible.builtin.template
# user → ansible.builtin.user
# group → ansible.builtin.group