Section 1: CloudFormation Internals
In our first section, we will do a small refresher on CloudFormation. Later, we will dive deep into its core component – a template – and learn how to write universal, redundant, and reusable templates.
This section comprises the following chapters:
- Chapter 1, CloudFormation Refresher
- Chapter 2, Advanced Template Development
Chapter 1
CloudFormation Refresher
Cloud computing introduced a brand-new way of managing the infrastructure.
As the demand for the AWS cloud grew, the usual routine and operational tasks became troublesome. The AWS cloud allowed any type of business to rapidly grow and solve all the business needs regarding compute power; however, the need to maintain a certain stack of resources was hard.
DevOps culture brought a set of methodologies and ways of working, and one of those is called infrastructure as code. This process is about treating your infrastructure—network, virtual machines, storages, databases, and so on—as a computer program.
AWS CloudFormation was developed to solve this kind of problem.
You will already have some working knowledge of CloudFormation, but before we dive deep into learning advanced template development and how to provision at scale, use CloudFormation with CI/CD pipelines, and extend its features, let's quickly refresh our memory and look again at what CloudFormation is and how we use it.
In this chapter, we will learn the following:
- The internals of AWS CloudFormation
- Creating and updating a CloudFormation stack
- Managing permissions for CloudFormation
- Detecting unmanaged changes in our stack
Technical requirements
The code used in this chapter can be found in the book's GitHub repository at https://github.com/PacktPublishing/Mastering-AWS-CloudFormation/tree/master/Chapter1.
Check out the following video to see the Code in Action:
https://bit.ly/2WbU5Lh
Understanding the internals of AWS CloudFormation
AWS services consist of three parts:
We interact with AWS by making calls to its API services. If we want to create an EC2 instance, then we need to perform a call, ec2:RunInstances.
When we develop our template and create a stack, we invoke the cloudformation:CreateStack API method. AWS CloudFormation will receive the command along with the template, validate it, and start creating resources, making API calls to various AWS services, depending on what we have declared for it.
If the creation of any resource fails, then CloudFormation will roll back the changes and delete the resources that were created before the failure. But if there are no mistakes during the creation process, we will see our resources provisioned across the account.
If we want to make changes to our stack, then all we need to do is update the template file and invoke the cloudformation:UpdateStack API method. CloudFormation will then update only those resources that have been changed. If the update process fails, then CloudFormation will roll the changes back and return the stack to the previous, healthy, state.
Now that we have this covered, let's start creating our stack.
Creating your first stack
I'm sure you've done this before.
We begin by developing our template first. This is going to be a simple S3 bucket. I'm going to use YAML template formatting, but you may use JSON formatting if you wish:
MyBucket.yaml
AWSTemplateFormatVersion: "2010-09-09"
Description: This is my first bucket
Resources:
MyBucket:
Type: AWS::S3::Bucket
Now we just need to create the stack with awscli:
$ aws cloudformation create-stack \
--stack-name mybucket\
--template-body file://MyBucket.yaml
After a while, we will see our bucket created if we go to the AWS console or run aws s3 ls.
Now let's add some public access to our bucket:
MyBucket.yaml
AWSTemplateFormatVersion: "2010-09-09"
Description: This is my first bucket
Resources:
MyBucket:
Type: AWS::S3::Bucket
Properties:
AccessControl: PublicRead
Let's run the update operation:
$ aws cloudformation update-stack \
--stack-name mybucket \
--template-body file://MyBucket.yaml
To clean up your workspace, simply delete your stack using the following command:
$ aws cloudformation delete-stack --stack-name mybucket
Let's now look at the CloudFormation IAM permissions.
Understanding CloudFormation IAM permissions
We already know that CloudFormation performs API calls when we create or update the stack. Now the question is, does CloudFormation have the same powers as a root user?
When you work with production-grade AWS accounts, you need to control access to your environment for both humans (yourself and your coworkers) and machines (build systems, AWS resources, and so on). That is why controlling access for CloudFormation is important.
By default, when the user runs stack creation, they invoke the API method cloudformation:CreateStack. CloudFormation will use that user's access to invoke other API ...
