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. (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.
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 # main 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/ # ""
Alternatively you can put each inventory file with its
host_vars in a separate directory. This is particularly useful if your
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 Organizing host and group 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 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.
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
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 Roles for more information.
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
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.
If a playbook has a
./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.
Learn about YAML syntax
Review the basic playbook features
Browse existing collections, modules, and plugins
Learn how to extend Ansible by writing your own modules
Learn about how to select hosts
Complete playbook files from the github project source
Questions? Help? Ideas? Stop by the list on Google Groups
© 2012–2018 Michael DeHaan
© 2018–2021 Red Hat, Inc.
Licensed under the GNU General Public License version 3.