Infrastructure as code (IaC) (for example, AWS CloudFormation)

What is Infrastructure as Code (IaC), and can you explain how AWS CloudFormation fits into this concept?

Infrastructure as Code (IaC) refers to the practice of managing and provisioning computer data centers through machine-readable definition files, rather than physical hardware configuration or interactive configuration tools. AWS CloudFormation is an IaC service that allows users to define their AWS resources in a declarative way using JSON or YAML templates. With AWS CloudFormation, users can create, manage, and update resource stacks programmatically, ensuring that the infrastructure is consistent and repeatable.

How does AWS CloudFormation handle resource dependencies during stack creation or updates?

AWS CloudFormation automatically identifies and manages dependencies between resources in a template. When you create or update a stack, CloudFormation analyzes the relationship between resources and provisions or updates them in the correct order to respect dependencies. Users can also use the “DependsOn” attribute to explicitly define the creation order for specific resources that have a dependency.

Can you describe the difference between AWS CloudFormation stacks and stack sets?

An AWS CloudFormation stack is a collection of AWS resources that are managed as a single unit. It is based on a CloudFormation template which defines the resources and their relationship. A stack set, on the other hand, extends the concept of a stack by allowing you to create, update, or delete stacks across multiple accounts and regions with a single operation. This helps in maintaining consistency across complex environments that span across regions and accounts.

In AWS CloudFormation, what are the benefits of using nested stacks?

Nested stacks are stacks created as part of other stacks. The primary benefits of using nested stacks include modularity, reusability, and simplified management. Nested stacks allow architects to organize complex environments by modularizing templates into smaller, reusable components, which can be managed and updated independently. This can lead to cleaner and more maintainable code.

Explain how you would update an existing AWS CloudFormation stack without causing downtime for the current application.

To update an existing AWS CloudFormation stack without causing downtime, you can use strategies like rolling updates, blue-green deployment, or use update policies such as Auto Scaling groups’ update policies. In the case of stateless applications, you can implement updates that replace only one batch of instances at a time, maintaining the availability of the application. For stateful applications, you can use AWS CloudFormation custom resources or Lambda functions to manage complex updates and data migrations.

What is a Change Set in AWS CloudFormation, and how would you use it?

A Change Set in AWS CloudFormation is a summary of proposed changes to a stack. Before updating a stack with new resources or modified settings, a Change Set can be created to preview the changes that AWS CloudFormation will execute. It allows for reviewing the changes and confirming that they are as intended before they are actually applied, which helps to prevent unintended modifications.

How can you integrate AWS CloudFormation with other AWS services for continuous integration or continuous delivery workflows?

AWS CloudFormation can be integrated with services such as AWS CodePipeline, AWS CodeCommit, AWS CodeBuild, and AWS CodeDeploy to enable continuous integration and continuous delivery (CI/CD) workflows. By using these tools together, you can automate the process of code updates, testing, and deploying infrastructure changes, which simplifies and accelerates the release process while reducing the potential for human error.

Describe how you would manage sensitive information, such as database passwords, in an AWS CloudFormation template.

In an AWS CloudFormation template, sensitive information like database passwords should not be hardcoded. Instead, they can be managed using AWS Systems Manager Parameter Store or AWS Secrets Manager, which securely store and retrieve sensitive information. CloudFormation templates can then reference these values dynamically using the appropriate functions, such as Fn::GetAtt or Fn::Sub, ensuring that sensitive information remains secure and is not exposed in the template.

Can you explain what CloudFormation Drift Detection is, and why it’s important?

CloudFormation Drift Detection is a feature that allows users to detect whether their stack’s actual configuration differs, or has “drifted,” from the expected configuration defined in the CloudFormation template. By identifying configuration drift, you can ensure that the infrastructure is in compliance with your template’s definition, rectify unintended changes, and maintain consistency and integrity of your deployment. This is especially important for governance, compliance, and operational stability.

What would you do if a CloudFormation stack creation fails, and how can you analyze the cause of the failure?

If a CloudFormation stack creation fails, AWS CloudFormation rolls back the changes and deletes the resources that were created up to the point of failure. To analyze the cause, you can examine the events in the CloudFormation console, looking for the event marked as “ROLLBACK_IN_PROGRESS,” which indicates the point at which the failure occurred. Additionally, you can check CloudWatch logs if you have set up logging for CloudFormation. Once you identify the cause, you can correct the template and attempt to create the stack again.

Are there any limits in AWS CloudFormation that you should be aware of when architecting a solution, and how do you manage these limits?

Yes, AWS CloudFormation has several service limits, such as the number of stacks, stack layers, and parameters you can have. Understanding these limits is crucial when architecting solutions to ensure you do not exceed them. If you do hit these limits, you can request increases in some cases, optimize your templates by combining resources, or utilize nested stacks to organize resources more efficiently.

How does AWS CloudFormation provide support for blue/green deployment patterns?

AWS CloudFormation does not natively implement blue/green deployment patterns, but it can facilitate it. A blue/green deployment can be implemented by provisioning a new set of resources (the green environment) alongside the existing resources (the blue environment) in a new stack or updating an existing stack. Once the green environment is tested and validated, the traffic can be switched over from the blue environment to the green. This can be managed through DNS updates with Route 53 or load balancer settings. Afterwards, the blue environment can be decommissioned by deleting or updating the original stack.