The instructions define the use and work with Ansible Playbook, in addition to a quick introduction of their structure.
You can read about how to install Ansible on Ubuntu 18.04 in our other guide.
What is Ansible Playbooks?
A playbook in Ansible specifies a collection of some activities to be done and dealt with to specific collections of web servers. Unlike some other tuning tools, Playbook does not describe the state of the maker, as well as Ansible establishes all the changes that need to be made by itself. However, playbooks must be made as idempotents, which suggests that they can be run more than when without adverse repercussions.
Playbooks are usually utilized to carry out initial web server arrangement – including customers and directories, managing software packages as well as files.
A playbook is a YAML file that usually has the following structure:
---
- hosts: [target hosts]
remote_user: [yourname]
tasks:
- [task 1]
- [task 2]
For example, the following playbook will belong to all servers in the marketingservers group and will run the Apache web server:
---
-hosts: [marketingservers]
remote_user: webadmin
tasks:
- name: Ensure the Apache daemon has started
service:name=httpd state=started
become: yes
become_method: sudo
The playbook above shows an example of a task:
tasks:
- name: Ensure the Apache daemon has started
service:name=httpd state=started
become: yes
become_method: sudo
Each task should have a name that is subsequently logged and can help track progress. After the name line (name) is the module that will be launched, in this case it is the service module. Other attributes allow more options, the Ansible example allows sudo privileges.
Running Ansible Playbook
You can run the finished playbook using the following command:
ansible-playbook playbook.yml
For example:
ansible-playbook nginx.yml
However, if you want to filter the list of hosts so that the script only applies to one of those hosts, you can add a flag and specify a subset of the hosts in the file:
ansible-playbook -l host_subset playbook.yml
For example:
ansible-playbook -l host3 nginx.yml
Registration of results
When you install and configure services manually, you almost always need to know the outcome of your actions. You can configure this functionality using registration.
For each task, if desired, it is possible to log its result (failure or success) in a variable that can be checked later. When using this functionality, it’s a good idea to tell Ansible to ignore errors for such a task, as it’s common for the playbook to abort if there are any problems.
Thus, if you need to check whether a task has completed or not and decide on the next steps, you must use the registration functionality.
For example, let’s tell playbook to load the index.php file if it exists. If this task fails, the index.html file will start loading:
---
- hosts:droplets
tasks:
-name: Installs nginx webserver
apt: pkg=nginx state=installed update_cache=true
notify:
- start nginx
-name: Upload default index.php for host
copy: src=static_files/index.php dest=/usr/share/nginx/www/mode=0644
register: php
ignore_errors: True
-name: Remove index.html for host
command: rm /usr/share/nginx/www/index.html
when: php|success
-name: Upload default index.html for host
copy: src=static_files/index.html dest=/usr/share/nginx/www/mode=0644
when: php|failed
handlers:
- name: start nginx
service: name=nginx state=started
This script tries to upload a PHP file to the host. Ansible logs the success of the operation in a variable called php. If this operation was successful, the next task is to delete the index.html file. If the operation fails, the index.html file will be loaded.
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