395 lines
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ReStructuredText
395 lines
14 KiB
ReStructuredText
Intro to Playbooks
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==================
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.. _about_playbooks:
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About Playbooks
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```````````````
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Playbooks are a completely different way to use ansible than in adhoc task execution mode, and are
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particularly powerful.
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Simply put, playbooks are the basis for a really simple configuration management and multi-machine deployment system,
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unlike any that already exist, and one that is very well suited to deploying complex applications.
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Playbooks can declare configurations, but they can also orchestrate steps of
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any manual ordered process, even as different steps must bounce back and forth
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between sets of machines in particular orders. They can launch tasks
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synchronously or asynchronously.
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While you might run the main /usr/bin/ansible program for ad-hoc
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tasks, playbooks are more likely to be kept in source control and used
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to push out your configuration or assure the configurations of your
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remote systems are in spec.
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There are also some full sets of playbooks illustrating a lot of these techniques in the
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`ansible-examples repository <https://github.com/ansible/ansible-examples>`_. We'd recommend
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looking at these in another tab as you go along.
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There are also many jumping off points after you learn playbooks, so hop back to the documentation
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index after you're done with this section.
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.. _playbook_language_example:
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Playbook Language Example
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`````````````````````````
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Playbooks are expressed in YAML format (see :doc:`YAMLSyntax`) and have a minimum of syntax, which intentionally
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tries to not be a programming language or script, but rather a model of a configuration or a process.
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Each playbook is composed of one or more 'plays' in a list.
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The goal of a play is to map a group of hosts to some well defined roles, represented by
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things ansible calls tasks. At a basic level, a task is nothing more than a call
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to an ansible module, which you should have learned about in earlier chapters.
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By composing a playbook of multiple 'plays', it is possible to
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orchestrate multi-machine deployments, running certain steps on all
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machines in the webservers group, then certain steps on the database
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server group, then more commands back on the webservers group, etc.
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"plays" are more or less a sports analogy. You can have quite a lot of plays that affect your systems
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to do different things. It's not as if you were just defining one particular state or model, and you
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can run different plays at different times.
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For starters, here's a playbook that contains just one play::
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---
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- hosts: webservers
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vars:
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http_port: 80
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max_clients: 200
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remote_user: root
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tasks:
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- name: ensure apache is at the latest version
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yum: pkg=httpd state=latest
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- name: write the apache config file
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template: src=/srv/httpd.j2 dest=/etc/httpd.conf
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notify:
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- restart apache
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- name: ensure apache is running
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service: name=httpd state=started
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handlers:
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- name: restart apache
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service: name=httpd state=restarted
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Below, we'll break down what the various features of the playbook language are.
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.. _playbook_basics:
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Basics
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``````
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.. _playbook_hosts_and_users:
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Hosts and Users
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+++++++++++++++
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For each play in a playbook, you get to choose which machines in your infrastructure
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to target and what remote user to complete the steps (called tasks) as.
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The `hosts` line is a list of one or more groups or host patterns,
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separated by colons, as described in the :doc:`intro_patterns`
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documentation. The `remote_user` is just the name of the user account::
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---
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- hosts: webservers
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remote_user: root
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.. note::
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The `remote_user` parameter was formerly called just `user`. It was renamed in Ansible 1.4 to make it more distinguishable from the `user` module (used to create users on remote systems).
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Remote users can also be defined per task::
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---
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- hosts: webservers
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remote_user: root
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tasks:
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- name: test connection
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ping:
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remote_user: yourname
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.. note::
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The `remote_user` parameter for tasks was added in 1.4.
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Support for running things from sudo is also available::
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---
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- hosts: webservers
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remote_user: yourname
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sudo: yes
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You can also use sudo on a particular task instead of the whole play::
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---
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- hosts: webservers
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remote_user: yourname
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tasks:
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- service: name=nginx state=started
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sudo: yes
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You can also login as you, and then sudo to different users than root::
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---
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- hosts: webservers
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remote_user: yourname
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sudo: yes
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sudo_user: postgres
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If you need to specify a password to sudo, run `ansible-playbook` with ``--ask-sudo-pass`` (`-K`).
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If you run a sudo playbook and the playbook seems to hang, it's probably stuck at the sudo prompt.
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Just `Control-C` to kill it and run it again with `-K`.
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.. important::
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When using `sudo_user` to a user other than root, the module
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arguments are briefly written into a random tempfile in /tmp.
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These are deleted immediately after the command is executed. This
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only occurs when sudoing from a user like 'bob' to 'timmy', not
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when going from 'bob' to 'root', or logging in directly as 'bob' or
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'root'. If this concerns you that this data is briefly readable
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(not writable), avoid transferring uncrypted passwords with
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`sudo_user` set. In other cases, '/tmp' is not used and this does
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not come into play. Ansible also takes care to not log password
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parameters.
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.. _tasks_list:
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Tasks list
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++++++++++
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Each play contains a list of tasks. Tasks are executed in order, one
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at a time, against all machines matched by the host pattern,
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before moving on to the next task. It is important to understand that, within a play,
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all hosts are going to get the same task directives. It is the purpose of a play to map
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a selection of hosts to tasks.
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When running the playbook, which runs top to bottom, hosts with failed tasks are
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taken out of the rotation for the entire playbook. If things fail, simply correct the playbook file and rerun.
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The goal of each task is to execute a module, with very specific arguments.
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Variables, as mentioned above, can be used in arguments to modules.
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Modules are 'idempotent', meaning if you run them
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again, they will make only the changes they must in order to bring the
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system to the desired state. This makes it very safe to rerun
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the same playbook multiple times. They won't change things
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unless they have to change things.
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The `command` and `shell` modules will typically rerun the same command again,
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which is totally ok if the command is something like
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'chmod' or 'setsebool', etc. Though there is a 'creates' flag available which can
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be used to make these modules also idempotent.
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Every task should have a `name`, which is included in the output from
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running the playbook. This is output for humans, so it is
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nice to have reasonably good descriptions of each task step. If the name
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is not provided though, the string fed to 'action' will be used for
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output.
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Tasks can be declared using the legacy "action: module options" format, but
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it is recommended that you use the more conventional "module: options" format.
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This recommended format is used throughout the documentation, but you may
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encounter the older format in some playbooks.
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Here is what a basic task looks like. As with most modules,
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the service module takes key=value arguments::
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tasks:
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- name: make sure apache is running
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service: name=httpd state=running
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The `command` and `shell` modules are the only modules that just take a list
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of arguments and don't use the key=value form. This makes
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them work as simply as you would expect::
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tasks:
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- name: disable selinux
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command: /sbin/setenforce 0
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The command and shell module care about return codes, so if you have a command
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whose successful exit code is not zero, you may wish to do this::
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tasks:
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- name: run this command and ignore the result
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shell: /usr/bin/somecommand || /bin/true
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Or this::
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tasks:
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- name: run this command and ignore the result
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shell: /usr/bin/somecommand
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ignore_errors: True
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If the action line is getting too long for comfort you can break it on
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a space and indent any continuation lines::
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tasks:
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- name: Copy ansible inventory file to client
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copy: src=/etc/ansible/hosts dest=/etc/ansible/hosts
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owner=root group=root mode=0644
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Variables can be used in action lines. Suppose you defined
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a variable called 'vhost' in the 'vars' section, you could do this::
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tasks:
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- name: create a virtual host file for {{ vhost }}
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template: src=somefile.j2 dest=/etc/httpd/conf.d/{{ vhost }}
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Those same variables are usable in templates, which we'll get to later.
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Now in a very basic playbook all the tasks will be listed directly in that play, though it will usually
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make more sense to break up tasks using the 'include:' directive. We'll show that a bit later.
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.. _action_shorthand:
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Action Shorthand
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````````````````
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.. versionadded:: 0.8
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Ansible prefers listing modules like this in 0.8 and later::
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template: src=templates/foo.j2 dest=/etc/foo.conf
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You will notice in earlier versions, this was only available as::
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action: template src=templates/foo.j2 dest=/etc/foo.conf
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The old form continues to work in newer versions without any plan of deprecation.
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.. _handlers:
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Handlers: Running Operations On Change
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``````````````````````````````````````
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As we've mentioned, modules are written to be 'idempotent' and can relay when
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they have made a change on the remote system. Playbooks recognize this and
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have a basic event system that can be used to respond to change.
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These 'notify' actions are triggered at the end of each block of tasks in a playbook, and will only be
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triggered once even if notified by multiple different tasks.
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For instance, multiple resources may indicate
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that apache needs to be restarted because they have changed a config file,
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but apache will only be bounced once to avoid unnecessary restarts.
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Here's an example of restarting two services when the contents of a file
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change, but only if the file changes::
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- name: template configuration file
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template: src=template.j2 dest=/etc/foo.conf
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notify:
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- restart memcached
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- restart apache
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The things listed in the 'notify' section of a task are called
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handlers.
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Handlers are lists of tasks, not really any different from regular
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tasks, that are referenced by name. Handlers are what notifiers
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notify. If nothing notifies a handler, it will not run. Regardless
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of how many things notify a handler, it will run only once, after all
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of the tasks complete in a particular play.
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Here's an example handlers section::
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handlers:
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- name: restart memcached
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service: name=memcached state=restarted
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- name: restart apache
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service: name=apache state=restarted
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Handlers are best used to restart services and trigger reboots. You probably
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won't need them for much else.
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.. note::
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Notify handlers are always run in the order written.
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Roles are described later on. It's worthwhile to point out that handlers are
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automatically processed between 'pre_tasks', 'roles', 'tasks', and 'post_tasks'
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sections. If you ever want to flush all the handler commands immediately though,
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in 1.2 and later, you can::
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tasks:
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- shell: some tasks go here
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- meta: flush_handlers
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- shell: some other tasks
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In the above example any queued up handlers would be processed early when the 'meta'
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statement was reached. This is a bit of a niche case but can come in handy from
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time to time.
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.. _executing_a_playbook:
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Executing A Playbook
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````````````````````
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Now that you've learned playbook syntax, how do you run a playbook? It's simple.
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Let's run a playbook using a parallelism level of 10::
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ansible-playbook playbook.yml -f 10
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.. _ansible-pull:
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Ansible-Pull
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````````````
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Should you want to invert the architecture of Ansible, so that nodes check in to a central location, instead
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of pushing configuration out to them, you can.
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Ansible-pull is a small script that will checkout a repo of configuration instructions from git, and then
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run ansible-playbook against that content.
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Assuming you load balance your checkout location, ansible-pull scales essentially infinitely.
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Run ``ansible-pull --help`` for details.
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There's also a `clever playbook <https://github.com/ansible/ansible-examples/blob/master/language_features/ansible_pull.yml>`_ available to configure ansible-pull via a crontab from push mode.
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.. _tips_and_tricks:
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Tips and Tricks
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```````````````
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Look at the bottom of the playbook execution for a summary of the nodes that were targeted
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and how they performed. General failures and fatal "unreachable" communication attempts are
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kept separate in the counts.
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If you ever want to see detailed output from successful modules as well as unsuccessful ones,
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use the ``--verbose`` flag. This is available in Ansible 0.5 and later.
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Ansible playbook output is vastly upgraded if the cowsay
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package is installed. Try it!
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To see what hosts would be affected by a playbook before you run it, you
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can do this::
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ansible-playbook playbook.yml --list-hosts
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.. seealso::
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:doc:`YAMLSyntax`
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Learn about YAML syntax
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:doc:`playbooks_best_practices`
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Various tips about managing playbooks in the real world
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:doc:`index`
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Hop back to the documentation index for a lot of special topics about playbooks
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:doc:`modules`
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Learn about available modules
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:doc:`developing_modules`
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Learn how to extend Ansible by writing your own modules
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:doc:`intro_patterns`
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Learn about how to select hosts
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`Github examples directory <https://github.com/ansible/ansible-examples>`_
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Complete end-to-end playbook examples
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`Mailing List <http://groups.google.com/group/ansible-project>`_
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Questions? Help? Ideas? Stop by the list on Google Groups
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