Basics

Basic Concepts for using Chef

Updated: 03 September 2023

Basics of Chef

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Infrastructure Automation > Learn the Basics > Ubuntu > Docker

Note About Environment

I am running a VM with access to a Shared Drive using VirtualBox, this can be found at root/media/sf_name on the Ubuntu VM

Set Up a Docker Container to Manage

We’ll make use of a Docker container with Ubuntu to work with Chef - generally though Docker containers are treated as immutable infrastructure

Before starting we will need to ensure that Docker is installed on our system so that we can run chef in the container

Make a Working Directory

Make a new directory in which we can work

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mkdir learn-chef
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cd learn-chef

Start the Docker Container

Download the Ubuntu 14.04 image from Docker hub and start the container

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docker pull ubuntu:14:04

From the shared learn-chef directory, run the following command

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$ docker run -it -v $(pwd):/root/chef-repo -p 8100:80 ubuntu:14.04 /bin/bash

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PS> docker run -it -v ${pwd}:/root/chef-repo -p 8100:80 ubuntu:14.04 /bin/bash

Running the container as above will expose also give our docker container access to our system ~ /chef-repo directory so that we can edit our chef code directly from there

From the Container

Update the container package list and install curl

Install Chef in Container

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apt-get update
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apt-get install curl -y

Next we can run Chef Workstation as follows:

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curl https://omnitruck.chef.io/install.sh | sudo bash -s -- -P chef-workstation -c stable -v 0.2.41

Set Up the Working Directory

From the container cd into the ~/chef-repo directory that we initialized previously

In this directory (the same as your local learn-chef) directory, create the initial MOTD file by using chef-client in local mode (usually chef-client will download the latest code from a server though)

Inside of the chef-repo directory create a file called hello.rb with the following content

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file '/tmp/motd' do
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  content 'hello world'
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end

And then run the above file with the following command

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chef-client --local-mode hello.rb

This will create a new file /tmp/motd which contains the text hello world

We can view the contents of this file using more or cat

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more /tmp/motd

If we run the chef-client command again we will see that no resources were updated

We can update the hello.rb file contents to contain the following

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file '/tmp/motd' do
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  content 'hello chef'
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end

And then update the resource with

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chef-client --local-mode hello.rb

And we will see that the file was updated with the following

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- update content in file /tmp/motd from b94d27 to c38c60
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--- /tmp/motd  2019-02-11 14:47:29.431735359 +0000
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+++ /tmp/.chef-motd20190211-4014-8rvcal  2019-02-11 14:53:48.291735359 +0000
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@@ -1,2 +1,2 @@
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-hello world
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+hello chef

If we manually change the /tmp/motd file, running chef-client will restore the correct configuration

You can test this by running the following command to modify the file

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echo 'hello robots' > /tmp/motd

And then having chef restore it

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chef-client --local-mode hello.rb

Chef endsures that the actual state of a resource matches the state that was specified, even if it is altered by an external resource. Usually we configure chef-client to run periodically or as part of a continuous automation system which helps our resources be correctly configured

Delete MOTD file

Create a file called goodbye.rb with the following contents

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file '/tmp/motd' do
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  action :delete
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end

Then use the chef-client to run it

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chef-client --local-mode goodbye.rb

This will give us the following output

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Recipe: @recipe_files::/root/chef-repo/goodbye.rb
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  * file[/tmp/motd] action delete
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    - delete file /tmp/motd

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more /tmp/motd
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#/tmp/motd: No such file or directory

Summary

Resources describe the what, not the how. A recipe is a file that describes what state a part of the system should be in, but not how to get there - that is handled by Chef

Resources have actions, such as :delete which is a process by which a desired state is reached. Every resource has a default action, such as create a file or install a package. :create is the defult action for a file resource

Recipes are an ordered list of configuration states and typically contain related states

Configure a Package and Service

Packages and services, like files, are also resource types

For this portion we will be managing an Apache HTTP Server Package and its associated Service

Update Apt Cache

We can run the apt-get update command manually every time we bring up an instance, but chef provides us with an apt_update resource to automate the process

Chef allows us to periodically carry out a specific task, in this case we can update our apt cache every 24 hours (86 400 seconds)

In the chef-repo directory create a webserver.rb file with the instructions to periodically update the cache as follows

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apt_update 'Update the apt cache daily' do
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  frequency 86_400
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  action :periodic
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end

Instead of :periodic we can also use the :update action to update each time chef runs

Install the Apache Package

Next we can install the apache2 package, modify the webserver.rb package to do this

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apt_update 'Update the apt cache daily' do
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  frequency 86_400
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  action :periodic
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end
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package 'apache2'

We don’t need to specify the :install action as this is the default

Now run the recipe with

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chef-client --local-mode webserver.rb

Typically (if not the root user) we need to run Chef with sudo

Start and Enable the Apache Service

Update the webserver.rb file to enable the Apache service when the server boots and then start the service, this is one by way of the action list given in which the following actions on a resource will be carried out

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apt_update 'Update the apt cache daily' do
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  frequency 86_400
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  action :periodic
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end
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package 'apache2'
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service 'apache2' do
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  supports status: true
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  action [:enable, :start]
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end

Now re-run the recipe in order to start the service

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chef-client --local-mode webserver.rb

Add a Home Page

We can use the file resource to create a homepage for our site at /var/www/html/index.html with a basic hello world message. This can be added to the webserver.rb recipe as follows

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apt_update 'Update the apt cache daily' do
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  frequency 86_400
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  action :periodic
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end
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package 'apache2'
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service 'apache2' do
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  supports status: true
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  action [:enable, :start]
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end
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file '/var/www/html/index.html' do
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  content '<html>
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  <body>
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    <h1>hello world</h1>
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  </body>
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</html>'
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end

And we can run chef-client to apply it

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chef-client --local-mode webserver.rb

If we do not see any errors we can continue and make an HTTP request with curl inside the container, making a curl to localhost will by default hit port 80, we can do this from the container as follows

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curl localhost

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curl localhost:80

Furthermore we can view this on the host machine’s browser due to the port forwarding we initially set up for the container -p 8100:80 on which maps port 80 on the container to 8100 on the host. We can do this simply by visiting localhost:8100 from the host or making an HTTP request from the terminal

Summary

Chef allows us to automate and configure multiple resource types as well as carry out tasks periodically, manage installed packages, and specify actions for those packages

Making Recipes More Managable

The problem with the recipe we are currently using is that the HTML for the webpage was embedded in the recipe, this is not practical. In order to more easily reference external files we can make use of a Cookbook

Create a Cookbook

From the chef-repo directory create a cookbooks directory, in this run the use Chef to generate a Cookbook named learn_chef_apache2

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mkdir cookbooks
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chef generate cookbook cookbooks/learn_chef_apache2

The cookbooks/learn_chef_apache2 part tells chef to create a new Cookbook in the cookbooks directory called learn_chef_apache2

Thereafter install tree on the container so that we can view the directory structure and then look at the cookbooks directory

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apt-get install tree -y
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tree cookbooks

The file structure can be seen to be:

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cookbooks
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`-- learn_chef_apache2
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    |-- Berksfile
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    |-- CHANGELOG.md
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    |-- LICENSE
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    |-- README.md
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    |-- chefignore
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    |-- metadata.rb
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    |-- recipes
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    |   `-- default.rb
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    |-- spec
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    |   |-- spec_helper.rb
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    |   `-- unit
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    |       `-- recipes
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    |           `-- default_spec.rb
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    `-- test
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        `-- integration
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            `-- default
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                `-- default_test.rb

The default recipe is in the recipes/default.rb file, our recipe will be written in there

Create a Template

A new template file can be generated with the chef generate command, generate a new template called index.html as follows

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chef generate template cookbooks/learn_chef_apache2 index.html

Move the index.html content we made previously to a template file which will be added as templates/index.html.erb into which we must add the following

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<html>
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  <body>
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    <h1>hello cookbook</h1>
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  </body>
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</html>

We have added the content directly into the cookbook for the purpose of the tutorial, but realstically the application would be some set of build artifacts that will then be pulled from a build server to be deployed

Update the Recipe

Now update the recipe in the default.rb file to once again update the apt cache, start the Apache Web Server, and reference the HTML template with the following

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apt_update 'Update the apt cache daily' do
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  frequency 86_400
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  action :periodic
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end
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package 'apache2'
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service 'apache2' do
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  supports status: true
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  action [:enable, :start]
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end
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template '/var/www/html/index.html' do
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  source 'index.html.erb'
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end

Run the Cookbook

chef-client can be used to run the Cookbook, we will again use the --local-mode flag and specify the required recipes with the --runlist flag

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chef-client --local-mode --runlist 'recipe[learn_chef_apache2]'

Note the recipe[learn_chef_apache2] which specifies that we want to run the learn_chef_apache2’s default.rb recipe. This is the same as recipe[learn_chef_apache2::default]

We can check that the file was updated with

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curl localhost

And by visiting localhost:8100 on the Host