While it is possible to write a playbook in one file as we've done throughout this workshop, eventually you’ll want to reuse files and start to organize things.
Ansible Roles are the way we do this. When you create a role, you deconstruct your playbook into parts and those parts sit in a directory structure. This is explained in more detail in the best practice.
This exercise will cover:
- the folder structure of an Ansible Role
- how to build an Ansible Role
- creating an Ansible Play to use and execute a role
- using Ansible to create a Apache VirtualHost on node2
Roles follow a defined directory structure; a role is named by the top level directory. Some of the subdirectories contain YAML files, named main.yml. The files and templates subdirectories can contain objects referenced by the YAML files.
An example project structure could look like this, the name of the role would be "apache":
apache/
├── defaults
│ └── main.yml
├── files
├── handlers
│ └── main.yml
├── meta
│ └── main.yml
├── README.md
├── tasks
│ └── main.yml
├── templates
├── tests
│ ├── inventory
│ └── test.yml
└── vars
└── main.yml
The various main.yml files contain content depending on their location in the directory structure shown above. For instance, vars/main.yml references variables, handlers/main.yaml describes handlers, and so on. Note that in contrast to playbooks, the main.yml files only contain the specific content and not additional playbook information like hosts, become or other keywords.
Tip
There are actually two directories for variables:
varsanddefault: Default variables have the lowest precedence and usually contain default values set by the role authors and are often used when it is intended that their values will be overridden.. Variables can be set in eithervars/main.ymlordefaults/main.yml, but not in both places.
Using roles in a Playbook is straight forward:
---
- name: launch roles
hosts: web
roles:
- role1
- role2For each role, the tasks, handlers and variables of that role will be included in the Playbook, in that order. Any copy, script, template, or include tasks in the role can reference the relevant files, templates, or tasks without absolute or relative path names. Ansible will look for them in the role's files, templates, or tasks respectively, based on their use.
Ansible looks for roles in a subdirectory called roles in the project directory. This can be overridden in the Ansible configuration. Each role has its own directory. To ease creation of a new role the tool ansible-galaxy can be used.
Tip
Ansible Galaxy is your hub for finding, reusing and sharing the best Ansible content.
ansible-galaxyhelps to interact with Ansible Galaxy. For now we'll just using it as a helper to build the directory structure.
Okay, lets start to build a role. We'll build a role that installs and configures Apache to serve a virtual host. Run these commands in your ~/ansible-files directory:
[user@control ansible-files]$ mkdir roles
[user@control ansible-files]$ ansible-galaxy init --offline roles/apache_vhostHave a look at the role directories and their content:
[user@control ansible-files]$ tree rolesroles/
└── apache_vhost
├── defaults
│ └── main.yml
├── files
├── handlers
│ └── main.yml
├── meta
│ └── main.yml
├── README.md
├── tasks
│ └── main.yml
├── templates
├── tests
│ ├── inventory
│ └── test.yml
└── vars
└── main.yml
The main.yml file in the tasks subdirectory of the role should do the following:
- Make sure httpd is installed
- Make sure httpd is started and enabled
- Put HTML content into the Apache document root
- Install the template provided to configure the vhost
WARNING
The
main.yml(and other files possibly included by main.yml) can only contain tasks, not complete playbooks!
Edit the roles/apache_vhost/tasks/main.yml file:
---
- name: install httpd
yum:
name: httpd
state: latest
- name: start and enable httpd service
service:
name: httpd
state: started
enabled: trueNote that here just tasks were added. The details of a playbook are not present.
The tasks added so far do:
- Install the httpd package using the yum module
- Use the service module to enable and start httpd
Next we add two more tasks to ensure a vhost directory structure and copy html content:
- name: ensure vhost directory is present
file:
path: "/var/www/vhosts/{{ ansible_hostname }}"
state: directory
- name: deliver html content
copy:
src: web.html
dest: "/var/www/vhosts/{{ ansible_hostname }}/index.html"Note that the vhost directory is created/ensured using the file module.
The last task we add uses the template module to create the vhost configuration file from a j2-template:
- name: template vhost file
template:
src: vhost.conf.j2
dest: /etc/httpd/conf.d/vhost.conf
owner: root
group: root
mode: 0644
notify:
- restart_httpdNote it is using a handler to restart httpd after an configuration update.
The full tasks/main.yml file is:
---
- name: install httpd
yum:
name: httpd
state: latest
- name: start and enable httpd service
service:
name: httpd
state: started
enabled: true
- name: ensure vhost directory is present
file:
path: "/var/www/vhosts/{{ ansible_hostname }}"
state: directory
- name: deliver html content
copy:
src: web.html
dest: "/var/www/vhosts/{{ ansible_hostname }}/index.html"
- name: template vhost file
template:
src: vhost.conf.j2
dest: /etc/httpd/conf.d/vhost.conf
owner: root
group: root
mode: 0644
notify:
- restart_httpdCreate the handler in the file roles/apache_vhost/handlers/main.yml to restart httpd when notified by the template task:
---
# handlers file for roles/apache_vhost
- name: restart_httpd
service:
name: httpd
state: restartedCreate the HTML content that will be served by the webserver.
- Create an web.html file in the "src" directory of the role,
files:
#> echo 'simple vhost index' > ~/ansible-files/roles/apache_vhost/files/web.html- Create the
vhost.conf.j2template file in the role'stemplatessubdirectory.
#> cat roles/apache_vhost/templates/vhost.conf.j2# {{ ansible_managed }}
<VirtualHost *:8080>
ServerAdmin webmaster@{{ ansible_fqdn }}
ServerName {{ ansible_fqdn }}
ErrorLog logs/{{ ansible_hostname }}-error.log
CustomLog logs/{{ ansible_hostname }}-common.log common
DocumentRoot /var/www/vhosts/{{ ansible_hostname }}/
<Directory /var/www/vhosts/{{ ansible_hostname }}/>
Options +Indexes +FollowSymlinks +Includes
Order allow,deny
Allow from all
</Directory>
</VirtualHost>
You are ready to test the role against node2. But since a role cannot be assigned to a node directly, first create a playbook which connects the role and the host. Create the file test_apache_role.yml in the directory ~/ansible-files:
---
- name: use apache_vhost role playbook
hosts: node2
become: true
pre_tasks:
- debug:
msg: 'Beginning web server configuration.'
roles:
- apache_vhost
post_tasks:
- debug:
msg: 'Web server has been configured.'Note the pre_tasks and post_tasks keywords. Normally, the tasks of roles execute before the tasks of a playbook. To control order of execution pre_tasks are performed before any roles are applied. The post_tasks are performed after all the roles have completed. Here we just use them to better highlight when the actual role is executed.
Now you are ready to run your playbook:
[user@control ansible-files]$ ansible-playbook test_apache_role.ymlRun a curl command against node2 to confirm that the role worked:
[user@control ansible-files]$ curl -s http://node2:8080
simple vhost indexCongratulations! You have successfully completed this exercise!
Did the final curl work? You can see what ports the web server is running by using the netstat command:
#> sudo netstat -tulpnThere should be a line like this:
tcp6 0 0 :::8080 :::* LISTEN 25237/httpdIf it is not working make sure that /etc/httpd/conf/httpd.conf has Listen 8080 in it. This should have been changed by Exercise 1.5
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