Understanding the internals of AWS CloudFormation

AWS services consist of three parts:

• API
• Backend
• Storage

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.