You have learned about playbooks, inventory, roles, and variables. This section pulls all those elements together, outlining a sample setup for automating a web service. You can find more example playbooks illustrating these patterns in our `ansible-examples repository <https://github.com/ansible/ansible-examples>`_. (NOTE: These may not use all of the features in the latest release, but are still an excellent reference!).
The sample setup organizes playbooks, roles, inventory, and variables files by function, with tags at the play and task level for greater granularity and control. This is a powerful and flexible approach, but there are other ways to organize Ansible content. Your usage of Ansible should fit your needs, not ours, so feel free to modify this approach and organize your content as you see fit.
..contents::
:local:
Sample directory layout
-----------------------
This layout organizes most tasks in roles, with a single inventory file for each environment and a few playbooks in the top-level directory::
production # inventory file for production servers
staging # inventory file for staging environment
group_vars/
group1.yml # here we assign variables to particular groups
group2.yml
host_vars/
hostname1.yml # here we assign variables to particular systems
hostname2.yml
library/ # if any custom modules, put them here (optional)
module_utils/ # if any custom module_utils to support modules, put them here (optional)
filter_plugins/ # if any custom filter plugins, put them here (optional)
site.yml # master playbook
webservers.yml # playbook for webserver tier
dbservers.yml # playbook for dbserver tier
tasks/ # task files included from playbooks
webservers-extra.yml # <-- avoids confusing playbook with task files
roles/
common/ # this hierarchy represents a "role"
tasks/ #
main.yml # <-- tasks file can include smaller files if warranted
handlers/ #
main.yml # <-- handlers file
templates/ # <-- files for use with the template resource
ntp.conf.j2 # <------- templates end in .j2
files/ #
bar.txt # <-- files for use with the copy resource
foo.sh # <-- script files for use with the script resource
vars/ #
main.yml # <-- variables associated with this role
defaults/ #
main.yml # <-- default lower priority variables for this role
meta/ #
main.yml # <-- role dependencies
library/ # roles can also include custom modules
module_utils/ # roles can also include custom module_utils
lookup_plugins/ # or other types of plugins, like lookup in this case
webtier/ # same kind of structure as "common" was above, done for the webtier role
monitoring/ # ""
fooapp/ # ""
.. note: By default, Ansible assumes your playbooks are stored in one directory with roles stored in a sub-directory called ``roles/``. As you use Ansible to automate more tasks, you may want to move your playbooks into a sub-directory called ``playbooks/``. If you do this, you must configure the path to your ``roles/`` directory using the ``roles_path`` setting in ansible.cfg.
Alternative directory layout
----------------------------
Alternatively you can put each inventory file with its ``group_vars``/``host_vars`` in a separate directory. This is particularly useful if your ``group_vars``/``host_vars`` don't have that much in common in different environments. The layout could look something like this::
inventories/
production/
hosts # inventory file for production servers
group_vars/
group1.yml # here we assign variables to particular groups
group2.yml
host_vars/
hostname1.yml # here we assign variables to particular systems
hostname2.yml
staging/
hosts # inventory file for staging environment
group_vars/
group1.yml # here we assign variables to particular groups
group2.yml
host_vars/
stagehost1.yml # here we assign variables to particular systems
stagehost2.yml
library/
module_utils/
filter_plugins/
site.yml
webservers.yml
dbservers.yml
roles/
common/
webtier/
monitoring/
fooapp/
This layout gives you more flexibility for larger environments, as well as a total separation of inventory variables between different environments. However, this approach is harder to maintain, because there are more files. For more information on organizing group and host variables, see :ref:`splitting_out_vars`.
.._groups_and_hosts:
Sample group and host variables
-------------------------------
These sample group and host variables files record the variable values that apply to each machine or group of machines. For instance, the data center in Atlanta has its own NTP servers, so when setting up ntp.conf, we should use them::
---
# file: group_vars/atlanta
ntp: ntp-atlanta.example.com
backup: backup-atlanta.example.com
Similarly, the webservers have some configuration that does not apply to the database servers::
---
# file: group_vars/webservers
apacheMaxRequestsPerChild: 3000
apacheMaxClients: 900
Default values, or values that are universally true, belong in a file called group_vars/all::
---
# file: group_vars/all
ntp: ntp-boston.example.com
backup: backup-boston.example.com
If necessary, you can define specific hardware variance in systems in a host_vars file::
---
# file: host_vars/db-bos-1.example.com
foo_agent_port: 86
bar_agent_port: 99
Again, if you are using :ref:`dynamic inventory <dynamic_inventory>`, Ansible creates many dynamic groups automatically. So a tag like "class:webserver" would load in variables from the file "group_vars/ec2_tag_class_webserver" automatically.
.._split_by_role:
Sample playbooks organized by function
--------------------------------------
With this setup, a single playbook can define all the infrastructure. The site.yml playbook imports two other playbooks, one for the webservers and one for the database servers::
---
# file: site.yml
- import_playbook: webservers.yml
- import_playbook: dbservers.yml
The webservers.yml file, also at the top level, maps the configuration of the webservers group to the roles related to the webservers group::
---
# file: webservers.yml
- hosts: webservers
roles:
- common
- webtier
With this setup, you can configure your whole infrastructure by "running" site.yml, or run a subset by running webservers.yml. This is analogous to the Ansible "--limit" parameter but a little more explicit::
ansible-playbook site.yml --limit webservers
ansible-playbook webservers.yml
.._role_organization:
Sample task and handler files in a function-based role
Ansible loads any file called ``main.yml`` in a role sub-directory. This sample ``tasks/main.yml`` file is simple - it sets up NTP, but it could do more if we wanted::
---
# file: roles/common/tasks/main.yml
- name: be sure ntp is installed
yum:
name: ntp
state: present
tags: ntp
- name: be sure ntp is configured
template:
src: ntp.conf.j2
dest: /etc/ntp.conf
notify:
- restart ntpd
tags: ntp
- name: be sure ntpd is running and enabled
service:
name: ntpd
state: started
enabled: yes
tags: ntp
Here is an example handlers file. As a review, handlers are only fired when certain tasks report changes, and are run at the end
of each play::
---
# file: roles/common/handlers/main.yml
- name: restart ntpd
service:
name: ntpd
state: restarted
See :ref:`playbooks_reuse_roles` for more information.
.._organization_examples:
What the sample setup enables
-----------------------------
The basic organizational structure described above enables a lot of different automation options. To reconfigure your entire infrastructure::
ansible-playbook -i production site.yml
To reconfigure NTP on everything::
ansible-playbook -i production site.yml --tags ntp
To reconfigure only the webservers::
ansible-playbook -i production webservers.yml
To reconfigure only the webservers in Boston::
ansible-playbook -i production webservers.yml --limit boston
To reconfigure only the first 10 webservers in Boston, and then the next 10::
ansible-playbook -i production webservers.yml --limit boston[0:9]
ansible-playbook -i production webservers.yml --limit boston[10:19]
The sample setup also supports basic ad-hoc commands::
ansible boston -i production -m ping
ansible boston -i production -m command -a '/sbin/reboot'
To discover what tasks would run or what hostnames would be affected by a particular Ansible command::
# confirm what task names would be run if I ran this command and said "just ntp tasks"
ansible-playbook -i production webservers.yml --tags ntp --list-tasks
# confirm what hostnames might be communicated with if I said "limit to boston"
ansible-playbook -i production webservers.yml --limit boston --list-hosts
.._dep_vs_config:
Organizing for deployment or configuration
------------------------------------------
The sample setup models a typical configuration topology. When doing multi-tier deployments, there are going
to be some additional playbooks that hop between tiers to roll out an application. In this case, 'site.yml'
may be augmented by playbooks like 'deploy_exampledotcom.yml' but the general concepts still apply. Ansible allows you to deploy and configure using the same tool, so you would likely reuse groups and keep the OS configuration in separate playbooks or roles from the app deployment.
Consider "playbooks" as a sports metaphor -- you can have one set of plays to use against all your infrastructure and situational plays that you use at different times and for different purposes.
.._ship_modules_with_playbooks:
Using local Ansible modules
---------------------------
If a playbook has a :file:`./library` directory relative to its YAML file, this directory can be used to add Ansible modules that will
automatically be in the Ansible module path. This is a great way to keep modules that go with a playbook together. This is shown
in the directory structure example at the start of this section.
