While Ansible ad hoc commands are useful for simple operations, they are not suited for complex configuration management or orchestration scenarios. For such use cases Playbooks are the way to go.
Playbooks are files which describe the desired configurations or steps to implement on managed hosts. Playbooks can change lengthy, complex administrative tasks into easily repeatable routines with predictable and successful outcomes.
A Playbook is where you can take some of those ad hoc commands you just ran and put them into a repeatable set of Plays and Tasks.
A Playbook can have multiple Plays and a Play can have one or multiple Tasks. In a Task a Module is called, like the Modules in the previous chapter.
Here is a nice analogy: When Ansible Modules are the tools in your workshop, the Inventory is the list of materials and the Playbooks are the instructions.
Playbooks are text files written in YAML format and therefore need:
to start with three dashes (---)
proper indentation using spaces and not tabs!
There are some important concepts:
hosts: the managed hosts to perform the tasks on
tasks: the operations to be performed by invoking Ansible modules and passing them the necessary options.
become: privilege escalation in Playbooks, same as using -b in the ad hoc command.
The ordering of the contents within a Playbook is important, because Ansible executes plays and tasks in the order they are presented.
A Playbook should be idempotent, so if a Playbook is run once to put the hosts in the correct state, it should be safe to run it a second time and it should make no further changes to the hosts.
Most Ansible modules are idempotent, so it is relatively easy to ensure this is true.
Enough theory, it’s time to create your first Playbook. In this lab you create a Playbook to set up an Apache webserver in three steps:
First step: Install httpd package
Second step: Enable/start httpd service
Third step: Create an index.html file
This Playbook makes sure the package containing the Apache webserver is installed on node1.
There is a best practice on the preferred directory structures for playbooks. We strongly encourage you to read and understand these practices as you develop your Ansible ninja skills. That said, our playbook today is very basic and creating a complex structure will just confuse things.
Instead, we are going to create a very simple directory structure for our playbook, and add just a couple of files to it.
In your browser, bring up your code-server terminal (you opened one in the first section) and create a directory called ansible-files in your home directory and change into it:
[student@ansible-1 ~]$ mkdir ansible-files
[student@ansible-1 ~]$ cd ansible-files/
Now use code-server to add a file called apache.yml with the following content.
If you are unsure how to use code-server (basically like VSCode), have a quick look at the Visual Studio Code Server introduction
---
- name: Apache server installed
hosts: node1
become: yes
This shows one of Ansible’s strengths: The Playbook syntax is easy to read and understand. In this Playbook:
A name is given for the play via name:.
The host to run the playbook against is defined via hosts:.
We enable user privilege escalation with become:.
You obviously need to use privilege escalation to install a package or run any other task that requires root permissions. This is done in the Playbook by become: yes.
Now that we’ve defined the play, let’s add a task to get something done. We will add a task in which yum will ensure that the Apache package is installed in the latest version. Modify the file so that it looks like the following listing using the code-server editor:
---
- name: Apache server installed
hosts: node1
become: yes
tasks:
- name: latest Apache version installed
yum:
name: httpd
state: latest
Since playbooks are written in YAML, alignment of the lines and keywords is crucial. Make sure to vertically align the t in task with the b in become. Once you are more familiar with Ansible, make sure to take some time and study a bit the YAML Syntax.
In the added lines:
We started the tasks part with the keyword tasks:.
A task is named and the module for the task is referenced. Here it uses the yum module.
Parameters for the module are added:
name: to identify the package name
state: to define the wanted state of the package
The module parameters are individual to each module. If in doubt, look them up again with ansible-doc.
Save your playbook.
Playbooks are executed using the ansible-playbook command on the control node. Before you run a new Playbook it’s a good idea to check for syntax errors. Head over to the code-server terminal and run:
[student@ansible-1 ansible-files]$ ansible-playbook --syntax-check apache.yml
Now you should be ready to run your Playbook:
[student@ansible-1 ansible-files]$ ansible-playbook apache.yml
The output should not report any errors but provide an overview of the tasks executed and a Play Recap summarizing what has been done. There is also a task called Gathering Facts listed: this is a built-in task that runs automatically at the beginning of each Play. It collects information about the managed nodes. Exercises later on will cover this in more detail.
Use SSH to make sure Apache has been installed on node1. The necessary IP address is provided in the inventory. Grep for the IP address there and use it to SSH to the node.
[student@ansible-1 ansible-files]$ grep node1 ~/lab_inventory/hosts
node1 ansible_host=11.22.33.44
[student@ansible-1 ansible-files]$ ssh 11.22.33.44
Last login: Wed May 15 14:03:45 2019 from 44.55.66.77
Managed by Ansible
[...]
[ec2-user@node1 ~]$ rpm -qi httpd
Name : httpd
Version : 2.4.6
[...]
Log out of node1 with the command exit so that you are back on the control host, and verify the installed package with an Ansible ad hoc command!
[student@ansible-1 ansible-files]$ ansible node1 -m command -a 'rpm -qi httpd'
Run the Playbook a second time, and compare the output: The output changed from changed to ok, and the color changed from yellow to green. Also the PLAY RECAP output is different now. This make it easy to spot what Ansible actually did.
The next part of the Playbook makes sure the Apache webserver is enabled and started on node1.
On the control host, as your student user, edit the file ~/ansible-files/apache.yml again to add a second task using the service module. The Playbook should now look like this:
---
- name: Apache server installed
hosts: node1
become: yes
tasks:
- name: latest Apache version installed
yum:
name: httpd
state: latest
- name: Apache enabled and running
service:
name: httpd
enabled: true
state: started
Again: what these lines do is easy to understand:
a second task is created and named
a module is specified (service)
parameters for the module are supplied
With the second task we make sure the Apache server is indeed running on the target machine. Run your extended Playbook:
[student@ansible-1 ansible-files]$ ansible-playbook apache.yml
Note the output now: Some tasks are shown as ok in green and one is shown as changed in yellow.
Use an Ansible ad hoc command again to make sure Apache has been enabled and started, e.g. with: systemctl status httpd.
Run the Playbook a second time to get used to the change in the output.
Check that the tasks were executed correctly and Apache is accepting connections: Make an HTTP request using Ansible’s uri module in an ad hoc command from the control node. Make sure to replace the IP with the IP for the node from the inventory.
Expect a lot of red lines and a 403 status
[student@ansible-1 ansible-files]$ ansible localhost -m uri -a "url=http://<IP>"
There are a lot of red lines and an error: As long as there is not at least an index.html file to be served by Apache, it will throw an ugly HTTP Error 403: Forbidden status and Ansible will report an error.
So why not use Ansible to deploy a simple index.html file? Create the file ~/ansible-files/index.html on the control node:
<body>
<h1>Apache is running fine</h1>
</body>
You already used Ansible’s copy module to write text supplied on the command line into a file. Now you’ll use the module in your Playbook to actually copy a file:
On the control node as your student user edit the file ~/ansible-files/apache.yml and add a new task utilizing the copy module. It should now look like this:
---
- name: Apache server installed
hosts: node1
become: yes
tasks:
- name: latest Apache version installed
yum:
name: httpd
state: latest
- name: Apache enabled and running
service:
name: httpd
enabled: true
state: started
- name: copy index.html
copy:
src: ~/ansible-files/index.html
dest: /var/www/html/
You are getting used to the Playbook syntax, so what happens? The new task uses the copy module and defines the source and destination options for the copy operation as parameters.
Run your extended Playbook:
[student@ansible-1 ansible-files]$ ansible-playbook apache.yml
Have a good look at the output
Run the ad hoc command using the “uri” module from further above again to test Apache: The command should now return a friendly green “status: 200” line, amongst other information.
This was nice but the real power of Ansible is to apply the same set of tasks reliably to many hosts.
node1 and node2 and node3?As you might remember, the inventory lists all nodes as members of the group web:
[web]
node1 ansible_host=11.22.33.44
node2 ansible_host=22.33.44.55
node3 ansible_host=33.44.55.66
The IP addresses shown here are just examples, your nodes will have different IP addresses.
Change the Playbook to point to the group web:
---
- name: Apache server installed
hosts: web
become: yes
tasks:
- name: latest Apache version installed
yum:
name: httpd
state: latest
- name: Apache enabled and running
service:
name: httpd
enabled: true
state: started
- name: copy index.html
copy:
src: ~/ansible-files/index.html
dest: /var/www/html/
Now run the Playbook:
[student@ansible-1 ansible-files]$ ansible-playbook apache.yml
Finally check if Apache is now running on all servers. Identify the IP addresses of the nodes in your inventory first, and afterwards use them each in the ad hoc command with the uri module as we already did with the node1 above. All output should be green.