Skip to content

Latest commit

 

History

History
344 lines (246 loc) · 13 KB

README.md

File metadata and controls

344 lines (246 loc) · 13 KB
Raw

Workshop Exercise - Writing Your First Playbook

Table of Contents

Objective

This exercise covers using Ansible to build two Apache web servers on Red Hat Enterprise Linux. This exercise covers the following Ansible fundamentals:

Guide

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. The goal of a play is to map a group of hosts. The goal of a task is to implement modules against those hosts.

Tip

Here is a nice analogy: When Ansible modules are the tools in your workshop, the inventory is the materials and the Playbooks are the instructions.

Step 1 - Playbook Basics

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.

Warning

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.

Tip

Most Ansible modules are idempotent, so it is relatively easy to ensure this is true.

Step 2 - Creating a Directory Structure and File for your Playbook

Enough theory, it’s time to create your first Ansible Playbook. In this lab you create a playbook to set up an Apache web server in three steps:

  1. Install httpd package
  2. Enable/start httpd service
  3. Copy over an web.html file to each web host

This Playbook makes sure the package containing the Apache web server 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.

On your control host ansible, create a directory called ansible-files in your home directory and change directories into it:

[user@control ~]$ mkdir ansible-files
[user@control ~]$ cd ansible-files/

Add a file called apache.yml with the following content. As discussed in the previous exercises, use vi/vim or, if you are new to editors on the command line, check out the editor intro again.

---
- 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:.

Tip

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:

---
- name: Apache server installed
  hosts: node1
  become: yes
  tasks:
  - name: latest Apache version installed
    yum:
      name: httpd
      state: latest

Tip

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

Tip

The module parameters are individual to each module. If in doubt, look them up again with ansible-doc.

Save your playbook and exit your editor.

Step 3 - Running the Playbook

Ansible 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:

[user@control ansible-files]$ ansible-playbook --syntax-check apache.yml

Now you should be ready to run your playbook:

[user@control 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 there: this is an 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.

Connect to node1 via SSH to make sure Apache has been installed:

[user@control ansible-files]$ ssh node1
Last login: Wed May 15 14:03:45 2019 from 44.55.66.77
Managed by Ansible

Use the command rpm -qi httpd to verify httpd is installed:

[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!

[user@control 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" is different now. This make it easy to spot what Ansible actually did.

Step 4 - Extend your Playbook: Start & Enable Apache

The next part of the Ansible Playbook makes sure the Apache application is enabled and started on node1.

On the control host, as your student user, edit the file ~/ansible-files/apache.yml 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

Thus with the second task we make sure the Apache server is indeed running on the target machine. Run your extended Playbook:

[user@control 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.

Step 5 - Extend your Playbook: Create an web.html

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.

Warning

Expect a lot of red lines and a 403 status!

[user@control 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 web.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 web.html file? On the ansible control host, as the user user, create the directory files to hold file resources in ~/ansible-files/:

[user@control ansible-files]$ mkdir files

Then create the file ~/ansible-files/files/web.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 commandline 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 web.html
    copy:
      src: web.html
      dest: /var/www/html/index.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:

[user@control 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.

Step 6 - Practice: Apply to Multiple Host

This was nice but the real power of Ansible is to apply the same set of tasks reliably to many hosts.

  • So what about changing the apache.yml Playbook to run on node1 and node2 and node3?

As you might remember, the inventory lists all nodes as members of the group web:

[web]
node1 ansible_host=192.168.55.201
node2 ansible_host=192.168.55.202
node3 ansible_host=192.168.55.203

Tip

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 web.html
    copy:
      src: web.html
      dest: /var/www/html/index.html

Now run the Playbook:

[user@control ansible-files]$ ansible-playbook apache.yml

Finally check if Apache is now running on both 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.

Tip

An alternative way to verify that Apache is running on both servers is to use the command ansible node2,node3 -m uri -a "url=http://localhost/".

Navigation
Previous Exercise - Next Exercise

Click here to return to the Ansible for Red Hat Enterprise Linux Workshop