.. _playbooks_delegation: Controlling where tasks run: delegation and local actions ========================================================= By default Ansible gathers facts and executes all tasks on the machines that match the ``hosts`` line of your playbook. This page shows you how to delegate tasks to a different machine or group, delegate facts to specific machines or groups, or run an entire playbook locally. Using these approaches, you can manage inter-related environments precisely and efficiently. For example, when updating your webservers, you might need to remove them from a load-balanced pool temporarily. You cannot perform this task on the webservers themselves. By delegating the task to localhost, you keep all the tasks within the same play. .. contents:: :local: Tasks that cannot be delegated ------------------------------ Some tasks always execute on the controller. These tasks, including ``include``, ``add_host``, and ``debug``, cannot be delegated. .. _delegation: Delegating tasks ---------------- If you want to perform a task on one host with reference to other hosts, use the ``delegate_to`` keyword on a task. This is ideal for managing nodes in a load balanced pool or for controlling outage windows. You can use delegation with the :ref:`serial <rolling_update_batch_size>` keyword to control the number of hosts executing at one time:: --- - hosts: webservers serial: 5 tasks: - name: Take out of load balancer pool ansible.builtin.command: /usr/bin/take_out_of_pool {{ inventory_hostname }} delegate_to: 127.0.0.1 - name: Actual steps would go here ansible.builtin.yum: name: acme-web-stack state: latest - name: Add back to load balancer pool ansible.builtin.command: /usr/bin/add_back_to_pool {{ inventory_hostname }} delegate_to: 127.0.0.1 The first and third tasks in this play run on 127.0.0.1, which is the machine running Ansible. There is also a shorthand syntax that you can use on a per-task basis: ``local_action``. Here is the same playbook as above, but using the shorthand syntax for delegating to 127.0.0.1:: --- # ... tasks: - name: Take out of load balancer pool local_action: ansible.builtin.command /usr/bin/take_out_of_pool {{ inventory_hostname }} # ... - name: Add back to load balancer pool local_action: ansible.builtin.command /usr/bin/add_back_to_pool {{ inventory_hostname }} You can use a local action to call 'rsync' to recursively copy files to the managed servers:: --- # ... tasks: - name: Recursively copy files from management server to target local_action: ansible.builtin.command rsync -a /path/to/files {{ inventory_hostname }}:/path/to/target/ Note that you must have passphrase-less SSH keys or an ssh-agent configured for this to work, otherwise rsync asks for a passphrase. To specify more arguments, use the following syntax:: --- # ... tasks: - name: Send summary mail local_action: module: community.general.mail subject: "Summary Mail" to: "{{ mail_recipient }}" body: "{{ mail_body }}" run_once: True The `ansible_host` variable reflects the host a task is delegated to. .. _delegate_facts: Delegating facts ---------------- Delegating Ansible tasks is like delegating tasks in the real world - your groceries belong to you, even if someone else delivers them to your home. Similarly, any facts gathered by a delegated task are assigned by default to the `inventory_hostname` (the current host), not to the host which produced the facts (the delegated to host). To assign gathered facts to the delegated host instead of the current host, set ``delegate_facts`` to ``true``:: --- - hosts: app_servers tasks: - name: Gather facts from db servers ansible.builtin.setup: delegate_to: "{{ item }}" delegate_facts: true loop: "{{ groups['dbservers'] }}" This task gathers facts for the machines in the dbservers group and assigns the facts to those machines, even though the play targets the app_servers group. This way you can lookup `hostvars['dbhost1']['ansible_default_ipv4']['address']` even though dbservers were not part of the play, or left out by using `--limit`. .. _local_playbooks: Local playbooks --------------- It may be useful to use a playbook locally on a remote host, rather than by connecting over SSH. This can be useful for assuring the configuration of a system by putting a playbook in a crontab. This may also be used to run a playbook inside an OS installer, such as an Anaconda kickstart. To run an entire playbook locally, just set the ``hosts:`` line to ``hosts: 127.0.0.1`` and then run the playbook like so:: ansible-playbook playbook.yml --connection=local Alternatively, a local connection can be used in a single playbook play, even if other plays in the playbook use the default remote connection type:: --- - hosts: 127.0.0.1 connection: local .. note:: If you set the connection to local and there is no ansible_python_interpreter set, modules will run under /usr/bin/python and not under {{ ansible_playbook_python }}. Be sure to set ansible_python_interpreter: "{{ ansible_playbook_python }}" in host_vars/localhost.yml, for example. You can avoid this issue by using ``local_action`` or ``delegate_to: localhost`` instead. .. seealso:: :ref:`playbooks_intro` An introduction to playbooks :ref:`playbooks_strategies` More ways to control how and where Ansible executes `Ansible Examples on GitHub <https://github.com/ansible/ansible-examples>`_ Many examples of full-stack deployments `User Mailing List <https://groups.google.com/group/ansible-devel>`_ Have a question? Stop by the google group! `irc.freenode.net <http://irc.freenode.net>`_ #ansible IRC chat channel