457 lines
17 KiB
ReStructuredText
457 lines
17 KiB
ReStructuredText
Advanced Playbooks
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==================
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Here are some advanced features of the playbooks language. Using all of these features
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are not neccessary, but many of them will prove useful. If a feature doesn't seem immediately
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relevant, feel free to skip it. For many people, the features documented in `playbooks` will
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be 90% or more of what they use in Ansible.
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Tags
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````
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(New in 0.6) If you have a large playbook it may become useful to be able to run a specific
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part of the configuration. Both plays and tasks support a "tags:" attribute for this reason.
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Example::
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tasks:
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- action: yum name=$item state=installed
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with_items:
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- httpd
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- memcached
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tags:
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- packages
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- action: template src=templates/src.j2 dest=/etc/foo.conf
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tags:
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- configuration
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If you wanted to just run the "configuration" and "packages" part of a very long playbook, you could do this::
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ansible-playbook example.yml --tags "configuration,packages"
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Playbooks Including Playbooks
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`````````````````````````````
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(New in 0.6) To further advance the concept of include files, playbook files can include other playbook
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files. Suppose you define the behavior of all your webservers in "webservers.yml" and
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all your database servers in "dbservers.yml". You can create a "site.yml" that would
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reconfigure all of your systems like this::
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----
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- include: playbooks/webservers.yml
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- include: playbooks/dbservers.yml
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This concept works great with tags to rapidly select exactly what plays you want to run, and exactly
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what parts of those plays.
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Ignoring Failed Commands
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````````````````````````
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(New in 0.6) Generally playbooks will stop executing any more steps on a host that has a failure.
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Sometimes, though, you want to continue on. To do so, write a task that looks like this::
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- name: this will not be counted as a failure
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action: command /bin/false
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ignore_errors: True
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Accessing Complex Variable Data
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```````````````````````````````
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Some provided facts, like networking information, are made available as nested data structures. To access
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them a simple '$foo' is not sufficient, but it is still easy to do. Here's how we get an IP address::
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${ansible_eth0.ipv4.address}
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It is also possible to access variables whose elements are arrays::
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${somelist[0]}
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And the array and hash reference syntaxes can be mixed.
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In templates, the simple access form still holds, but they can also be accessed from Jinja2 in more Python-native ways if
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that is preferred::
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{{ ansible_eth0["ipv4"]["address"] }}
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Accessing Information About Other Hosts
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```````````````````````````````````````
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If your database server wants to check the value of a 'fact' from another node, or an inventory variable
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assigned to another node, it's easy to do so within a template or even an action line::
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${hostvars.hostname.factname}
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.. note::
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No database or other complex system is required to exchange data
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between hosts. The hosts that you want to reference data from must
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be included in either the current play or any previous play.
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Additionally, *group_names* is a list (array) of all the groups the current host is in. This can be used in templates using Jinja2 syntax to make template source files that vary based on the group membership (or role) of the host::
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{% if 'webserver' in group_names %}
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# some part of a configuration file that only applies to webservers
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{% endif %}
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*groups* is a list of all the groups (and hosts) in the inventory. This can be used to enumerate all hosts within a group.
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For example::
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{% for host in groups['app_servers'] %}
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# something that applies to all app servers.
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{% endfor %}
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Use cases include pointing a frontend proxy server to all of the app servers, setting up the correct firewall rules between servers, etc.
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*inventory_hostname* is the name of the hostname as configured in Ansible's inventory host file. This can
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be useful for when you don't want to rely on the discovered hostname `ansible_hostname` or for other mysterious
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reasons. If you have a long FQDN, *inventory_hostname_short* (in Ansible 0.6) also contains the part up to the first
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period.
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Don't worry about any of this unless you think you need it. You'll know when you do.
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Variable File Seperation
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````````````````````````
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It's a great idea to keep your playbooks under source control, but
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you may wish to make the playbook source public while keeping certain
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important variables private. Similarly, sometimes you may just
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want to keep certain information in different files, away from
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the main playbook.
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You can do this by using an external variables file, or files, just like this::
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---
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- hosts: all
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user: root
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vars:
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favcolor: blue
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vars_files:
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- /vars/external_vars.yml
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tasks:
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- name: this is just a placeholder
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action: command /bin/echo foo
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This removes the risk of sharing sensitive data with others when
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sharing your playbook source with them.
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The contents of each variables file is a simple YAML dictionary, like this::
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---
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# in the above example, this would be vars/external_vars.yml
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somevar: somevalue
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password: magic
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.. note::
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It's also possible to keep per-host and per-group variables in very
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similar files, this is covered in :ref:`patterns`.
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Prompting For Sensitive Data
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````````````````````````````
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You may wish to prompt the user for certain input, and can
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do so with the similarly named 'vars_prompt' section. This has uses
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beyond security, for instance, you may use the same playbook for all
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software releases and would prompt for a particular release version
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in a push-script::
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---
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- hosts: all
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user: root
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vars:
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from: "camelot"
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vars_prompt:
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name: "what is your name?"
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quest: "what is your quest?"
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favcolor: "what is your favorite color?"
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There are full examples of both of these items in the github examples/playbooks directory.
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An alternative form of vars_prompt allows for hiding input from the user, and may later support
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some other options, but otherwise works equivalently::
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vars_prompt:
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- name: "some_password"
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prompt: "Enter password"
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private: True
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- name: "release_version"
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prompt: "Product release version"
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private: False
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Passing Variables On The Command Line
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`````````````````````````````````````
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In addition to `vars_prompt` and `vars_files`, it is possible to send variables over
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the ansible command line. This is particularly useful when writing a generic release playbook
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where you may want to pass in the version of the application to deploy::
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ansible-playbook release.yml --extra-vars "version=1.23.45 other_variable=foo"
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This is useful, for, among other things, setting the hosts group or the user for the playbook.
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Example::
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-----
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- user: $user
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hosts: $hosts
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tasks:
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- ...
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ansible-playbook release.yml --extra-vars "hosts=vipers user=starbuck"
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Conditional Execution
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`````````````````````
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Sometimes you will want to skip a particular step on a particular host. This could be something
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as simple as not installing a certain package if the operating system is a particular version,
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or it could be something like performing some cleanup steps if a filesystem is getting full.
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This is easy to do in Ansible, with the `only_if` clause, which actually is a Python expression.
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Don't panic -- it's actually pretty simple::
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vars:
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favcolor: blue
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is_favcolor_blue: "'$favcolor' == 'blue'"
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is_centos: "'$facter_operatingsystem' == 'CentOS'"
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tasks:
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- name: "shutdown if my favorite color is blue"
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action: command /sbin/shutdown -t now
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only_if: '$is_favcolor_blue'
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Variables from tools like `facter` and `ohai` can be used here, if installed, or you can
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use variables that bubble up from ansible, which many are provided by the :ref:`setup` module. As a reminder,
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these variables are prefixed, so it's `$facter_operatingsystem`, not `$operatingsystem`. Ansible's
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built in variables are prefixed with `ansible_`.
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The only_if expression is actually a tiny small bit of Python, so be sure to quote variables and make something
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that evaluates to `True` or `False`. It is a good idea to use 'vars_files' instead of 'vars' to define
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all of your conditional expressions in a way that makes them very easy to reuse between plays
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and playbooks.
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You cannot use live checks here, like 'os.path.exists', so don't try.
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It's also easy to provide your own facts if you want, which is covered in :doc:`moduledev`. To run them, just
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make a call to your own custom fact gathering module at the top of your list of tasks, and variables returned
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there will be accessible to future tasks::
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tasks:
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- name: gather site specific fact data
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action: site_facts
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- action: command echo ${my_custom_fact_can_be_used_now}
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Conditional Imports
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```````````````````
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Sometimes you will want to do certain things differently in a playbook based on certain criteria.
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Having one playbook that works on multiple platforms and OS versions is a good example.
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As an example, the name of the Apache package may be different between CentOS and Debian,
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but it is easily handled with a minimum of syntax in an Ansible Playbook::
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---
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- hosts: all
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user: root
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vars_files:
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- "vars/common.yml"
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- [ "vars/$facter_operatingsystem.yml", "vars/os_defaults.yml" ]
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tasks:
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- name: make sure apache is running
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action: service name=$apache state=running
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.. note::
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The variable (`$facter_operatingsystem`) is being interpolated into
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the list of filenames being defined for vars_files.
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As a reminder, the various YAML files contain just keys and values::
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---
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# for vars/CentOS.yml
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apache: httpd
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somethingelse: 42
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How does this work? If the operating system was 'CentOS', the first file Ansible would try to import
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would be 'vars/CentOS.yml', followed up by '/vars/os_defaults.yml' if that file
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did not exist. If no files in the list were found, an error would be raised.
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On Debian, it would instead first look towards 'vars/Debian.yml' instead of 'vars/CentOS.yml', before
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falling back on 'vars/os_defaults.yml'. Pretty simple.
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To use this conditional import feature, you'll need facter or ohai installed prior to running the playbook, but
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you can of course push this out with Ansible if you like::
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# for facter
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ansible -m yum -a "pkg=facter ensure=installed"
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ansible -m yum -a "pkg=ruby-json ensure=installed"
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# for ohai
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ansible -m yum -a "pkg=ohai ensure=installed"
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Ansible's approach to configuration -- seperating variables from tasks, keeps your playbooks
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from turning into arbitrary code with ugly nested ifs, conditionals, and so on - and results
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in more streamlined & auditable configuration rules -- especially because there are a
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minimum of decision points to track.
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Loop Shorthand
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``````````````
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To save some typing, repeated tasks can be written in short-hand like so::
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- name: add user $item
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action: user name=$item state=present groups=wheel
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with_items:
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- testuser1
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- testuser2
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If you have defined a YAML list in a variables file, or the 'vars' section, you can also do::
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with_items: $somelist
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The above would be the equivalent of::
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- name: add user testuser1
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action: user name=testuser1 state=present groups=wheel
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- name: add user testuser2
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action: user name=testuser2 state=present groups=wheel
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In a future release, the yum and apt modules will use with_items to execute fewer package
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manager transactions.
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Selecting Files And Templates Based On Variables
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````````````````````````````````````````````````
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Sometimes a configuration file you want to copy, or a template you will use may depend on a variable.
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The following construct selects the first available file appropriate for the variables of a given host,
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which is often much cleaner than putting a lot of if conditionals in a template.
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The following example shows how to template out a configuration file that was very different between, say,
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CentOS and Debian::
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- name: template a file
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action: template src=$item dest=/etc/myapp/foo.conf
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first_available_file:
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- /srv/templates/myapp/${ansible_distribution}.conf
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- /srv/templates/myapp/default.conf
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Asynchronous Actions and Polling
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````````````````````````````````
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By default tasks in playbooks block, meaning the connections stay open
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until the task is done on each node. If executing playbooks with
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a small parallelism value (aka ``--forks``), you may wish that long
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running operations can go faster. The easiest way to do this is
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to kick them off all at once and then poll until they are done.
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You will also want to use asynchronous mode on very long running
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operations that might be subject to timeout.
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To launch a task asynchronously, specify its maximum runtime
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and how frequently you would like to poll for status. The default
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poll value is 10 seconds if you do not specify a value for `poll`::
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---
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- hosts: all
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user: root
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tasks:
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- name: simulate long running op (15 sec), wait for up to 45, poll every 5
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action: command /bin/sleep 15
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async: 45
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poll: 5
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.. note::
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There is no default for the async time limit. If you leave off the
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'async' keyword, the task runs synchronously, which is Ansible's
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default.
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Alternatively, if you do not need to wait on the task to complete, you may
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"fire and forget" by specifying a poll value of 0::
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---
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- hosts: all
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user: root
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tasks:
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- name: simulate long running op, allow to run for 45, fire and forget
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action: command /bin/sleep 15
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async: 45
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poll: 0
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.. note::
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You shouldn't "fire and forget" with operations that require
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exclusive locks, such as yum transactions, if you expect to run other
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commands later in the playbook against those same resources.
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.. note::
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Using a higher value for ``--forks`` will result in kicking off asynchronous
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tasks even faster. This also increases the efficiency of polling.
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Local Playbooks
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```````````````
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It may be useful to use a playbook locally, rather than by connecting over SSH. This can be useful
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for assuring the configuration of a system by putting a playbook on a crontab. This may also be used
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to run a playbook inside a OS installer, such as an Anaconda kickstart.
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To run an entire playbook locally, just set the "hosts:" line to "hosts:127.0.0.1" and then run the playbook like so::
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ansible-playbook playbook.yml --connection=local
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Alternatively, a local connection can be used in a single playbook play, even if other plays in the playbook
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use the default remote connection type::
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hosts: 127.0.0.1
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connection: local
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Turning Off Facts
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`````````````````
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If you know you don't need any fact data about your hosts, and know everything about your systems centrally, you
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can turn off fact gathering. This has advantages in scaling ansible in push mode with very large numbers of
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systems, mainly, or if you are using Ansible on experimental platforms. In any play, just do this::
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- hosts: whatever
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gather_facts: False
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Pull-Mode Playbooks
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```````````````````
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The use of playbooks in local mode (above) is made extremely powerful with the addition of `ansible-pull`.
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A script for setting up ansible-pull is provided in the examples/playbooks directory of the source
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checkout.
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The basic idea is to use Ansible to set up a remote copy of ansible on each managed node, each set to run via
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cron and update playbook source via git. This interverts the default push architecture of ansible into a pull
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architecture, which has near-limitless scaling potential. The setup playbook can be tuned to change
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the cron frequency, logging locations, and parameters to ansible-pull.
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This is useful both for extreme scale-out as well as periodic remediation. Usage of the 'fetch' module to retrieve
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logs from ansible-pull runs would be an excellent way to gather and analyze remote logs from ansible-pull.
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Style Points
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````````````
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Ansible playbooks are colorized. If you do not like this, set the ANSIBLE_NOCOLOR=1 environment variable.
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Ansible playbooks also look more impressive with cowsay installed, and we encourage installing this package.
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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`
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Review the basic playbook features
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:doc:`bestpractices`
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Various tips about playbooks in the real world
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:doc:`modules`
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Learn about available modules
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:doc:`moduledev`
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Learn how to extend Ansible by writing your own modules
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:doc:`patterns`
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Learn about how to select hosts
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`Github examples directory <https://github.com/ansible/ansible/tree/devel/examples/playbooks>`_
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Complete playbook files from the github project source
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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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