Composing and deploying IaC templates (for example, AWS Serverless Application Model [AWS SAM], AWS CloudFormation, AWS Cloud Development Kit [AWS CDK])

What is Infrastructure as Code (IaC), and why is it important in AWS cloud environments?

Infrastructure as Code (IAC) is a method of provisioning and managing computing resources through machine-readable definition files, rather than physical hardware configuration or interactive configuration tools. It’s important in AWS cloud environments because it enables consistent and predictable deployments, version control of infrastructure, and the ability to scale and replicate environments quickly and with less error.

Can you explain the difference between AWS CloudFormation and AWS CDK?

AWS CloudFormation is a service that provides a common language for describing and provisioning all the infrastructure resources in AWS environments. It allows you to use JSON or YAML templates to model and provision AWS resources. AWS CDK, on the other hand, is a software development framework for defining cloud infrastructure in code and provisioning it through AWS CloudFormation. It allows developers to define cloud resources using familiar programming languages like TypeScript, Python, Java, or C#.

What are some advantages of using the AWS Serverless Application Model (AWS SAM) over direct use of AWS CloudFormation for serverless deployments?

AWS SAM is an extension of AWS CloudFormation specifically designed for serverless applications. It provides shorthand syntax to express serverless resources, which makes it easier to read, write, and maintain serverless applications. SAM also includes a command line interface (CLI) that offers additional functionality for building, testing, and deploying serverless applications.

How can you ensure your AWS CloudFormation templates adhere to best security practices?

To ensure AWS CloudFormation templates follow best security practices, one should:

• Use IAM roles with the principle of least privilege for CloudFormation and the created resources.
• Reference SecureString parameters from AWS Systems Manager Parameter Store to manage secrets.
• Incorporate AWS resource policies to restrict access as needed.
• Include encryption settings on resources that support encryption in the template.
• Use template linting tools, such as cfn-lint and cfn-nag, to identify potential security issues in the templates.

What mechanisms can you use to update a stack safely in AWS CloudFormation without causing downtime or data loss?

To update a stack safely in AWS CloudFormation without causing downtime or data loss, you can use:

• Stack policies to prevent unintentional updates to critical resources.
• UpdateRollback policy to automatically roll back changes on failure.
• Change sets to preview proposed changes before applying them.
• Deletion policies on resources to preserve or create snapshots of stateful services like databases during updates.

How would you incorporate manual approval steps in an AWS CodePipeline that involves deployment of AWS CloudFormation templates?

To incorporate manual approval steps in AWS CodePipeline, you should use the Approval action type. You can add this approval action to the pipeline stage where you want the manual intervention to occur. This will pause the pipeline execution until someone with the right permissions approves or rejects the action.

Explain the concept of Nested Stacks in AWS CloudFormation. When would you use them?

Nested Stacks in AWS CloudFormation are stacks created as part of other stacks. They allow you to isolate repeated patterns or components of your architecture into separate templates and reuse them. Nested Stacks are useful to organize your architecture into logical parts and manage them separately, which is particularly helpful when dealing with large infrastructures or when you want to share and reuse certain components across different projects.

What are AWS CloudFormation Custom Resources and when should you use them?

AWS CloudFormation Custom Resources are placeholders that invoke AWS Lambda functions to manage resource creation, update, and deletion operations. You should use them when you need to provision resources that are not natively supported by AWS CloudFormation or to add functionality to your stack that requires custom logic during the stack operation.

Describe how you would automate the deployment of infrastructure across multiple AWS accounts or regions using AWS CloudFormation.

To automate deployment across multiple AWS accounts or regions, you could:

• Use AWS Organizations along with Service Control Policies (SCPs) to manage permissions across accounts.
• Employ AWS CloudFormation StackSets, which allows you to create, update, or delete stacks across multiple accounts and regions with a single operation.
• Utilize a CI/CD pipeline with cross-account roles and triggers to execute CloudFormation templates in different accounts and regions.

Explain how you could roll back a failed deployment in AWS CloudFormation.

When a deployment fails in AWS CloudFormation, it automatically rolls back to the previous stable state if rollback configuration is not disabled. This rollback undoes any changes made during the stack update. To manually roll back a change, you can either execute a new update with a previous version of the template or use the AWS CloudFormation console or AWS CLI to continue rollback to a prior working state.

What is drift detection in AWS CloudFormation, and how is it used?

Drift detection in AWS CloudFormation is a feature that identifies configuration changes that have been made to stack resources outside of CloudFormation. This allows you to compare the expected configuration of your stack’s resources as defined in CloudFormation templates with the current configuration of those resources in the AWS environment. Drift detection is used to maintain consistency and ensure that infrastructure is as code describes it.

How do you manage secrets when using AWS CloudFormation or AWS CDK to ensure they aren’t exposed in your templates?

To manage secrets without exposing them in AWS CloudFormation or AWS CDK templates, you can use AWS Secrets Manager or the AWS Systems Manager Parameter Store to reference secrets. Secrets are stored securely, and the templates only reference those secrets by their identifiers, not including the secret values within the template itself. Access to the secrets can be controlled through IAM policies and roles, ensuring that only authorized components or users can retrieve the actual secret values.