Top AWS CloudFormation Interview Questions (and Answers. 2023 Update)

In the article, we dive into the top AWS CloudFormation interview questions and their answers. We aim to help candidates prepare better by providing well-articulated answers with relevant code snippets where necessary. The interview questions are divided into the following three sections, with increasing difficultly or complexity:

AWS CloudFormation Interview Questions for Beginners

1. What is AWS CloudFormation and what is its relevance? (Fundamentals)

AWS CloudFormation is a service that helps you model and set up your Amazon Web Services resources so you can spend less time managing those resources and more time focusing on your applications that run in AWS. You create a template (in YAML or JSON format) that describes all the AWS resources that you want (like Amazon EC2 instances or Amazon RDS DB instances), and AWS CloudFormation takes care of provisioning and configuring those resources for you.

The relevance of AWS CloudFormation is that it provides a consistent and easy way to manage and provision resources in your AWS environment. It allows you to automate your infrastructure, leverage version control systems to keep track of changes, and reproduce your infrastructure at will, which are key benefits in a DevOps environment. It also ties into other AWS services like AWS Identity and Access Management (IAM) for access control, AWS S3 for template storage, and many others.

2. Can you explain the basic components of AWS CloudFormation? (Components, Fundamentals)

AWS CloudFormation has three main components:

  • Templates: These are the blueprints of your AWS infrastructure, written in JSON or YAML. They define the resources and properties.
  • Stacks: These are the actual collection of resources that have been provisioned and managed as a single unit from a CloudFormation template.
  • Change Sets: These allow you to preview how proposed changes to a stack might impact your resources.

3. How does CloudFormation work? (Fundamentals, Workflow)

When you create a CloudFormation stack, you start by designing a template. This template defines all the resources you want AWS to provision. You then submit this template to the CloudFormation service, and it will take care of creating all of the resources in the right order with the correct configurations.

Using CloudFormation to setup AWS Resources.
Using CloudFormation to setup AWS Resources. Image Source: AWS CloudFormation

CloudFormation also maintains the state of your stack resources, so if you need to make changes, you can update your template and CloudFormation will apply those changes in a controlled manner to the existing stack.

4. What are CloudFormation Templates? (Templates, Fundamentals)

CloudFormation Templates are the blueprint for your AWS resources. They are written in JSON or YAML and define all the AWS resources you want to provision. A CloudFormation template has several sections, such as the format version, a description, parameters, mappings, conditions, resources, and outputs.

5. How do you create a stack in AWS CloudFormation? (Stack Management, Usage)

You can create a stack in CloudFormation using the AWS Management Console, AWS CLI, or AWS SDKs. Here’s a basic example using AWS CLI:

aws cloudformation create-stack --stack-name MyStack --template-body file://template.json

This command will create a stack named “MyStack” using the template specified in the “template.json” file.

6. What is the difference between a stack and a stack set in AWS CloudFormation? (Stack Management, Fundamentals)

A stack is a collection of AWS resources that you can manage as a single unit. All the resources in a stack are defined by the stack’s AWS CloudFormation template.

A stack set on the other hand, extends the functionality of stacks to allow you to create, update, or delete stacks across multiple accounts and regions with a single operation. This is useful in an organization that has many AWS accounts and regions and wants to manage CloudFormation operations across them in a unified manner.

7. What does a typical AWS CloudFormation Template structure look like? (Templates, Fundamentals)

A typical AWS CloudFormation template contains the following main sections:

  • AWSTemplateFormatVersion: The AWS CloudFormation template version.
  • Description: A text string that describes the template.
  • Metadata: Objects that provide additional information about the template.
  • Parameters: Values to pass to your template at runtime.
  • Mappings: A mapping of keys and associated values.
  • Conditions: Conditions that control whether certain resources are created or whether certain resource properties are assigned a value.
  • Transform: For serverless applications, specifies the version of the AWS Serverless Application Model (SAM) to use.
  • Resources: Specifies the stack resources and their properties.
  • Outputs: Describes the values that are returned whenever you view your stack’s properties.

8. What are some common use cases for AWS CloudFormation? (Use Cases, Fundamentals)

AWS CloudFormation is typically used for:

  • Automating Deployment: Since everything is described in code, it can be version controlled and automated. This simplifies and speeds up deployment, especially in a Continuous Integration/Continuous Delivery (CI/CD) environment.
  • Managing and Updating Resources: CloudFormation allows you to manage resources as a stack. Therefore, updating or deleting a stack will automatically update or delete the corresponding resources.
  • Visualizing Resources and Dependencies: AWS provides a designer tool to visualize your CloudFormation templates, which can help with understanding the structure and dependencies of your resources.
  • Multi-Account/Multi-Region Deployment: With CloudFormation StackSets, you can manage resources across multiple accounts and regions, providing an easy way to set up complex environments.

9. What is an AWS CloudFormation Change Set? (Change Set, Usage)

A change set is a summary of proposed changes to a stack. You can create a change set by submitting changes for your stack, such as a modified template or different parameter values. AWS CloudFormation makes the changes to the stack only if you decide to execute the change set.

Change sets allow you to see how your changes might impact your running resources, especially for critical environments, before implementing them. This way, you can catch and fix any errors or potential disruptions before they affect your users.

10. Can you explain the difference between CloudFormation and Elastic Beanstalk? (Comparison, Fundamentals)

Both AWS CloudFormation and Elastic Beanstalk are orchestration tools, but they serve slightly different purposes:

  • AWS CloudFormation is designed to provision and manage complex environments at scale. It supports almost all AWS resources and provides detailed control over how they interconnect.
  • AWS Elastic Beanstalk is a Platform as a Service (PaaS) that helps developers deploy and manage applications in the AWS Cloud without worrying about the infrastructure that runs those applications. Elastic Beanstalk supports applications developed in Go, Java, .NET, Node.js, PHP, Python, and Ruby, as well as different application architecture types, including web applications, microservices, and APIs.

Therefore, Elastic Beanstalk might be better for simpler application deployments, while CloudFormation would be better for complex, multi-resource configurations.

In fact, Elastic Beanstalk uses CloudFormation under the hood to launch and manage the AWS resources needed for your application. You can even use CloudFormation to define and manage an Elastic Beanstalk environment and application.

For a deeper understanding of AWS CloudFormation and comparison with similar tools, check out our detailed comparison of CloudFormation vs CDK and Terraform vs CDK.

11. How would you update resources in a stack in AWS CloudFormation? (Stack Management, Usage)

AWS CloudFormation allows you to manage and provision AWS resources predictably and repeatedly. If you need to update the resources in a stack, you can do so by updating the stack. Here is a sample process you can follow:

  1. Navigate to the AWS CloudFormation console.
  2. Select the stack that you want to update.
  3. Choose the ‘Update’ option.
  4. In the ‘Specify template’ section, choose the ‘Replace current template’ option and then select the ‘Upload a template file’ option to upload your updated CloudFormation template.
  5. Choose the ‘Next’ button and provide any parameters required by the template.
  6. Choose the ‘Next’ button to review your changes and then the ‘Update stack’ button to update the stack with your changes.

If you’re using AWS CLI, you can use the aws cloudformation update-stack command. Here’s a sample command:

aws cloudformation update-stack --stack-name my-stack --template-body file://my-updated-stack.json --parameters ParameterKey=Param1,ParameterValue=newvalue

This command updates the ‘my-stack’ stack using the updated template file ‘my-updated-stack.json’, and sets the new parameter value for ‘Param1’.

12. What are helper scripts in AWS CloudFormation? (Helper Scripts, Usage)

AWS CloudFormation provides a set of Python scripts, known as helper scripts, that you can use to install software and start services on an Amazon EC2 instance. The helper scripts are:

  • cfn-init: Reads and interprets the metadata from the AWS::CloudFormation::Init key.
  • cfn-signal: A simple wrapper to signal an AWS CloudFormation WaitCondition, enabling you to synchronize other resources in the stack with the application being ready.
  • cfn-get-metadata: A wrapper script to retrieve metadata for a resource or path to a specific key.
  • cfn-hup: A daemon to check for updates to metadata and execute custom hooks when changes are detected.

These scripts help you to orchestrate your AWS CloudFormation deployments and make them more reliable and robust. Read more about helper scripts in our article AWS CloudFormation Best Practices.

13. What are some of the benefits of using AWS CloudFormation? (Benefits, Fundamentals)

AWS CloudFormation provides several benefits:

  • Automated Deployment: CloudFormation provides a consistent method for deploying resources across your organization, reducing manual efforts.
  • Predictability: With CloudFormation, you can preview changes to your infrastructure and application and apply changes across your environments in a controlled and predictable manner.
  • Infrastructure as Code: CloudFormation allows you to use programming languages or a simple text file to model and provision, in an automated and secure manner, all the resources needed for your applications across all regions and accounts.
  • Version Control: CloudFormation templates can be committed to version control systems, allowing you to track changes, implement standard practices, and roll back when necessary.

14. Can you explain the “Rollback” feature in AWS CloudFormation? (Features, Stack Management)

AWS CloudFormation’s Rollback feature is a powerful tool to ensure the integrity of your deployments. When you create or update a stack and it fails, AWS CloudFormation automatically rolls back all the changes to a point before the creation or update process began.

This rollback functionality ensures that if an error occurs during the deployment, your resources return to their original state, helping to prevent situations where resources are left in an inconsistent or non-functional state.

You can also manually trigger a rollback to a previously deployed stack state if needed. This feature helps with maintaining the resilience of your application and is part of AWS CloudFormation’s robust deployment management features.

15. What is the concept of Drift in AWS CloudFormation? (Drift, Stack Management)

Drift in AWS CloudFormation refers to the difference between the expected state of resources defined in CloudFormation stacks and the actual state of those resources in the AWS environment. Drift can occur when manual changes are made to resources that are part of a CloudFormation stack outside of CloudFormation.

For instance, if you manually change the instance type of an EC2 instance that’s part of a CloudFormation stack, that change introduces drift. AWS CloudFormation provides the ability to detect such drifts. It’s a good practice to minimize drift in your AWS environment to ensure that your infrastructure is in the desired and predictable state.

Drift detection helps maintain the consistency and reliability of your AWS resources and plays a crucial role in ensuring the integrity of your deployments. If you’re interested in understanding the best practices to manage your resources and maintain a drift-free environment, do read our detailed article on AWS CloudFormation Best Practices.

AWS CloudFormation Interview Questions for Experienced

16. How do you troubleshoot an AWS CloudFormation stack failure? (Troubleshooting, Stack Management)

Troubleshooting an AWS CloudFormation stack failure generally involves several steps:

  • First, identify the error message. AWS CloudFormation provides error messages in the AWS Management Console or via the AWS CLI. This message usually points to what caused the stack operation to fail.
  • If the error message is not clear enough, consider enabling CloudFormation Stack Events. These events provide a detailed history of the stack, helping to trace the failure cause.
  • AWS CloudFormation Drift Detection can also be used to compare the current stack configuration with the one defined in the CloudFormation template. Any discrepancies might be the root cause of the failure.

AWS CloudTrail can be utilized for more in-depth auditing and troubleshooting. Remember to follow the best practices for securing your AWS environment.

17. What are nested stacks in AWS CloudFormation? (Nested Stacks, Advanced Usage)

Nested Stacks are stacks created within other stacks. They allow you to break down large CloudFormation templates into smaller, more manageable pieces. Each nested stack is created using its own CloudFormation template, which is connected to a parent stack template through an AWS::CloudFormation::Stack resource.

Example of using nested stacks in CloudFormation to deploy a full workload consisting of database, middleware and UI tiers.

Here’s an example of how to reference a nested stack in a CloudFormation template:

Resources:
  MyNestedStack:
    Type: AWS::CloudFormation::Stack
    Properties:
      TemplateURL: https://s3.amazonaws.com/cloudformation-templates-us-east-2/MyNestedStackTemplate.yml

In this code, MyNestedStack is a nested stack that is created using the template at the specified S3 URL. This approach helps in modernizing monolith applications to microservices by managing resources related to a specific service in separate stack templates.

18. What is the importance of AWS Identity and Access Management (IAM) in AWS CloudFormation? (IAM, Security)

AWS Identity and Access Management (IAM) plays a critical role in AWS CloudFormation for securing and managing access to AWS resources. IAM allows you to control who can create and manage stacks, stack sets, and other CloudFormation resources in your AWS account.

IAM policies can define permissions for CloudFormation actions. For example, you can limit a user’s actions to only creating and viewing stacks but not deleting them. This can be crucial to prevent accidental deletion of important resources.

For best practices on IAM usage with CloudFormation and other services, see AWS IAM Best Practices.

19. What are mappings in AWS CloudFormation and when would you use them? (Mappings, Templates)

Mappings in AWS CloudFormation are a way to map keys to a set of associated name-value pairs. They allow you to specify conditional parameter values in your template, based on input parameters or other static values.

Here is an example of using mappings to specify different AMI IDs for different AWS regions:

Mappings: 
  RegionMap: 
    us-east-1: 
      HVM64: "ami-0ff8a91507f77f867"
    eu-west-1: 
      HVM64: "ami-047bb4163c506cd98"

Resources:
  MyEC2Instance:
    Type: 'AWS::EC2::Instance'
    Properties:
      ImageId: !FindInMap 
        - RegionMap
        - !Ref 'AWS::Region'
        - HVM64

In this code, !FindInMap is used to retrieve the appropriate AMI ID from the RegionMap mapping based on the current region.

20. How can you include files from an Amazon S3 bucket in a CloudFormation template? (Templates, S3, Advanced Usage)

You can include files from an Amazon S3 bucket in a CloudFormation template using the AWS::Include transform. This allows you to reference other files such as scripts, configuration files, or even other CloudFormation snippets in your template.

Here’s an example of how to use AWS::Include to insert a file from S3 into your CloudFormation template:

Resources:
  MyInstance:
    Type: 'AWS::EC2::Instance'
    Properties:
      UserData:
        'Fn::Base64': 
          'Fn::Transform':
            Name: 'AWS::Include'
            Parameters:
              Location: s3://my-bucket/my-script.sh

This code inserts the contents of the my-script.sh file from the specified S3 bucket into the UserData property of an EC2 instance.

Remember to secure your S3 transfers to prevent unauthorized access, as explained in our article on Securing FTP transfers to Amazon S3.

21. How can you use parameters in a CloudFormation Template? (Templates, Parameters)

In AWS CloudFormation, parameters are a way to pass values into your CloudFormation Template. They’re helpful for making templates reusable and customizable, as they allow you to input custom values each time you create a stack.

Here’s an example of how to define a parameter in a CloudFormation template:

Parameters:
  InstanceType:
    Description: The type of EC2 instance
    Type: String
    Default: t2.micro

In this example, InstanceType is a parameter we’ve defined. When you launch the stack using this template, you can choose a different instance type. If you don’t provide a value, the default, t2.micro, will be used.

To use this parameter elsewhere in your template, you would use the Ref function:

Resources:
  MyEC2Instance:
    Type: "AWS::EC2::Instance"
    Properties:
      InstanceType: 
        Ref: InstanceType
      ...

Here, the value of InstanceType will be passed to the InstanceType property of the MyEC2Instance resource.

22. Can you explain cross-stack references in AWS CloudFormation? (Cross-Stack References, Advanced Usage)

Cross-stack references allow you to use the output values from one CloudFormation stack in another stack. This is useful in managing complex infrastructures where you want to decouple the stacks but still share some information.

To create a cross-stack reference, you first define an Output in the exporting stack:

Outputs:
  VPCID:
    Description: The ID of the VPC
    Value: 
      Ref: MyVPC

Then, you can reference this output value in another stack using the Fn::ImportValue function:

Resources:
  MySubnet:
    Type: "AWS::EC2::Subnet"
    Properties:
      VpcId: 
        Fn::ImportValue: VPCID
      ...

In this example, VPCID is an output of another stack, and we’re using its value as the VpcId for a Subnet in the current stack. To learn more about cross-stack references, check out our comprehensive article on AWS CloudFormation StackSets.

23. What is AWS CloudFormation StackSet? (StackSet, Advanced Usage)

AWS CloudFormation StackSet is a feature that allows you to create, update, or delete stacks across multiple accounts and regions with a single operation. This is particularly useful in a multi-account and multi-region AWS environment, where managing resources individually can become quite complex.

The StackSet takes care of the order of operations across accounts and regions and retries failed operations. It’s a great tool for centralizing management and achieving consistent configuration across your AWS environment. We dive deep into the concept of StackSets in our AWS CloudFormation StackSets article.

24. What are Conditions in a CloudFormation Template and how are they used? (Templates, Conditions)

Conditions in a CloudFormation Template are used to control the creation of resources or the setting of properties based on runtime inputs. They help in creating more flexible and configurable templates.

Here’s an example of how conditions can be used in a CloudFormation template:

Parameters:
  EnvironmentType:
    Description: Environment type.
    Type: String
    Default: test
    AllowedValues:
      - prod
      - test
Conditions:
  IsProduction: 
    Fn::Equals: [!Ref EnvironmentType, prod]
Resources:
  MyBucket:
    Type: 'AWS::S3::Bucket'
    Properties:
      BucketName: 
        Fn::If:
          - IsProduction
          - my-prod-bucket
          - my-test-bucket

In this template, the condition IsProduction checks if EnvironmentType is prod. If it’s prod, the BucketName will be my-prod-bucket; otherwise, it will be my-test-bucket.

25. How can you handle sensitive information such as passwords in CloudFormation? (Security, Best Practices)

Handling sensitive information securely is a critical aspect of managing infrastructure. In AWS CloudFormation, you should never hard-code sensitive information in your templates. Instead, use AWS Systems Manager Parameter Store or AWS Secrets Manager to store sensitive data and reference them in your templates.

For instance, consider a template that creates a RDS database. You can retrieve the master password from the Secrets Manager:

Resources:
  MyDB:
    Type: "AWS::RDS::DBInstance"
    Properties:
      MasterUsername: admin
      MasterUserPassword: 
        Fn::Sub: '{{resolve:secretsmanager:mySecret:SecretString:password}}'
      ...

Here, mySecret is the name of the secret in Secrets Manager which stores the database password. This approach ensures that sensitive information is never exposed in plain text, and it’s managed securely with AWS’s built-in services.

To learn more about AWS security best practices, we suggest our article on AWS Security.

26. Can you explain the use of AWS CloudFormation Import Value function? (Functions, Advanced Usage)

The AWS CloudFormation Fn::ImportValue function is a handy tool when dealing with outputs from one stack that need to be inputs in another stack. This function allows you to import values that are exported by another stack.

Here’s a simple code snippet showing how it works:

Resources:
  MyVPC:
    Type: "AWS::EC2::VPC"
    Properties: 
      CidrBlock: "10.0.0.0/16"
Outputs:
  VPCId:
    Value: !Ref MyVPC
    Export:
      Name: My-VPC-Id-Export

In the above example, the ID of MyVPC is being exported as My-VPC-Id-Export. This value can now be imported in another stack as follows:

Resources:
  MySubnet:
    Type: "AWS::EC2::Subnet"
    Properties: 
      VpcId: 
        Fn::ImportValue: My-VPC-Id-Export
      CidrBlock: "10.0.0.0/24"

Here, Fn::ImportValue is used to import the VPC ID from the other stack into the current stack as an input for the MySubnet resource.

27. What are the different states of a stack in AWS CloudFormation? (Stack Management, Advanced Usage)

AWS CloudFormation stacks pass through several states during their lifecycle. Here are the most common states:

  • CREATE_IN_PROGRESS: AWS CloudFormation is creating resources in the stack.
  • CREATE_COMPLETE: All resources have been created successfully.
  • CREATE_FAILED: Resources failed to create.
  • ROLLBACK_IN_PROGRESS: AWS CloudFormation is deleting the stack due to a failed creation or a stack update that failed.
  • ROLLBACK_COMPLETE: AWS CloudFormation finished deleting the stack after a failed stack creation or update.
  • DELETE_IN_PROGRESS, DELETE_COMPLETE, and DELETE_FAILED: AWS CloudFormation is deleting, has finished deleting, or failed to delete the stack.
  • UPDATE_IN_PROGRESS, UPDATE_COMPLETE_CLEANUP_IN_PROGRESS, UPDATE_COMPLETE, and UPDATE_ROLLBACK_IN_PROGRESS, UPDATE_ROLLBACK_FAILED, and UPDATE_ROLLBACK_COMPLETE_CLEANUP_IN_PROGRESS, UPDATE_ROLLBACK_COMPLETE: These are states related to updating an existing stack.

For a more detailed look at stack states and transitions, you can refer to the official AWS documentation.

28. How do you handle circular dependencies in CloudFormation stacks? (Troubleshooting, Stack Management)

Circular dependencies in AWS CloudFormation occur when two or more resources depend on each other, leading to a situation where AWS CloudFormation can’t determine the correct creation order of resources.

To resolve such dependencies, it’s recommended to re-evaluate and modify the design of your infrastructure. It often involves breaking the circular dependency by rearranging or decoupling the resources. For example, if you have two resources A and B such that A depends on B and B depends on A, consider using CloudFormation’s Fn::If, Fn::Equals, and Fn::Not functions to create conditional resource properties or create separate CloudFormation templates to break the dependency cycle.

29. What is the concept of Stack Policy in AWS CloudFormation? (Stack Policy, Security)

A stack policy is a JSON document that defines the update actions that can be performed on designated resources in the stack. Stack policies provide an additional layer of security by preventing accidental updates to critical resources within a stack.

Here’s an example of a stack policy that prevents any updates to a specific DynamoDB resource:

{
  "Statement" : [
    {
      "Effect" : "Deny",
      "Action" : "Update:*",
      "Principal": "*",
      "Resource" : "LogicalResourceId/MyDynamoDBTable"
    },
    {
      "Effect" : "Allow",
      "Action" : "Update:*",
      "Principal": "*",
      "Resource" : "*"
    }
  ]
}

In the above policy, updates are denied to MyDynamoDBTable resource, while allowing updates to all other resources. You can learn more about stack policies in our article on AWS CloudFormation Security Best Practices.

30. What is the AWS CloudFormation Registry? (Registry, Advanced Usage)

The AWS CloudFormation Registry provides a centralized repository for managing and sharing CloudFormation modules and resource types within your AWS organization. You can use the registry to create, read, update, and delete resource types.

The CloudFormation Registry supports both private and public extensions. Private extensions are only visible and usable within the AWS account where they were registered, whereas public extensions can be shared across different AWS accounts.

It’s important to note that the CloudFormation Registry is different from the CloudFormation console. While the console is a user interface for managing and monitoring CloudFormation stacks, the registry is a repository for storing, sharing, and managing CloudFormation extensions.

For a detailed comparison of CloudFormation and other Infrastructure as Code (IaC) tools like AWS CDK and Terraform, you can refer to our comparison guide on CDK vs. CloudFormation or Terraform vs. CloudFormation.

AWS CloudFormation Interview Questions for Experts

31. How would you design an AWS CloudFormation template for large and complex infrastructures? (Design, Templates, Best Practices)

Designing AWS CloudFormation templates for large and complex infrastructures can be challenging due to the inherent complexities and dependencies. Here are some tips:

  • Modular Design: Build your infrastructure in a modular way. Each module can be a separate CloudFormation stack that represents a logical group of AWS resources.
  • Cross-stack References: Use cross-stack references to share outputs between stacks. This can help manage dependencies and avoid hardcoding values.
  • Nesting Stacks: For a more hierarchical approach, consider using nested stacks. This feature allows a stack to create other stacks, which can help manage larger systems and reduce repetition.

Here’s a basic example of a modular design in CloudFormation. This example creates an Amazon S3 bucket:

Resources:
  MyBucket:
    Type: "AWS::S3::Bucket"
    Properties: 
      BucketName: "example-bucket"

The Resources block defines the AWS resources that CloudFormation will create. In this case, an Amazon S3 bucket.

In a real-world scenario, your templates would include more complex resources and many different types of AWS services. You would then group related resources together in separate templates, creating a modular infrastructure design.

For more in-depth information, please refer to our guide on setting up Terraform and creating an EC2 instance using Terraform, which offers relevant tips and best practices for IaC (Infrastructure as Code).

32. Can you discuss best practices for using AWS CloudFormation at scale? (Best Practices, Scaling)

When using AWS CloudFormation at scale, several best practices can be applied:

  • Automation: As the number of CloudFormation stacks increases, automating deployments and updates becomes crucial. This can be done using AWS services like CodePipeline or third-party tools. (Related Article: Top 10 Modern Deployment Automation Tools)
  • Use AWS Service Limits: Ensure you are aware of AWS Service Limits. Design your templates in a way that they comply with these limits.
  • Effective Error Handling: Implement effective error handling strategies, including retries and back-offs.
  • Testing: Regularly test your CloudFormation templates to catch any errors early. AWS CloudFormation provides functionality to preview changes before deploying them.
  • Parallelize Resource Creation: Where possible, design your templates to allow AWS to create resources in parallel, speeding up deployment times.
  • Use StackSets for multi-region deployment: If your infrastructure spans multiple AWS regions, use AWS CloudFormation StackSets to manage your stacks across regions.

For additional insights on scaling your cloud infrastructure, you might find it useful to refer to our AWS Auto Scaling best practices guide.

33. How would you automate the deployment of AWS CloudFormation templates? (Automation, Best Practices)

Automation is a crucial part of managing CloudFormation templates. Here are some methods to automate the deployment:

  • AWS CLI: AWS Command Line Interface can be used to create and manage AWS CloudFormation stacks.
  • AWS SDKs: AWS provides Software Development Kits for various languages like Python, Java, and .NET. These can be used to automate CloudFormation operations.
  • AWS Management Console: Although not fully automated, the console provides a quick and easy way to create and manage stacks.
  • CI/CD pipelines: Integrating CloudFormation with CI/CD pipelines (such as AWS CodePipeline or Jenkins) provides automated testing and deployment.

For example, you can use the AWS CLI to deploy a CloudFormation stack:

aws cloudformation deploy --template-file /path_to_template/template.json --stack-name my-new-stack

This command creates a CloudFormation stack from the specified template file.

You might also find our guide on deployment automation tools useful, which covers more methods for automation.

34. How do you manage dependencies between multiple CloudFormation stacks? (Stack Management, Best Practices)

Dependencies between multiple AWS CloudFormation stacks can be managed using a few different approaches:

  • Cross-Stack References: This allows stacks to share resources by exporting an output value from one stack and importing it in another.
  • Nested Stacks: This allows a stack to create other stacks, which can help manage dependencies in a more hierarchical manner.
  • StackSets: These are used for deploying stacks across multiple accounts and regions, but can also be used to manage dependencies.

For more insights on managing dependencies, you might find it helpful to look at our guide on understanding Terraform workspace, which provides an in-depth understanding of dependencies in a multi-environment setup.

35. What are the limitations of AWS CloudFormation? (Limitations, Advanced Topics)

While AWS CloudFormation is a powerful service, it does come with certain limitations:

  • Template Size: The maximum size for a template that can be uploaded from an S3 Bucket is 1 MB, and from a local file is 51,200 bytes.
  • Resources and Parameters: Each template has a limit of 500 resources and 200 parameters.
  • Outputs: A single stack can have at most 200 outputs.
  • Mappings: A single mapping can have up to 200 unique keys, and a single template can include up to 200 mappings.
  • Stack Creation and Deletion: Stack creation and deletion times are limited to the AWS service quotas.

These limits can sometimes be increased by requesting a service limit increase from AWS. More information can be found in our detailed guide on AWS service limits and how to manage them.

While considering AWS CloudFormation, it’s essential to compare it with similar tools like Terraform or AWS CDK. Check out our CDK vs CloudFormation comparison and Terraform vs CDK comparison to make an informed decision.

36. How can you perform blue-green deployments using AWS CloudFormation? (Blue-Green Deployments, Advanced Usage)

Blue-green deployment is a release management strategy that reduces downtime and risk by running two identical environments, Blue and Green. At any given time, one of these environments, say Blue, is live. As you prepare a new version of your software, you do your staging on Green. When you are ready to deploy the new version, you switch the router so all incoming requests go to Green – your new live environment.

One way to perform blue-green deployments using AWS CloudFormation with the help of AWS Elastic Beanstalk. AWS Elastic Beanstalk provides a SwapEnvironmentCNAMEs action which swaps the CNAMEs for two environments.

Below is a CloudFormation template example to swap environment CNAMEs using the AWS CLI command within an AWS::CloudFormation::Init metadata block.

Resources:
  MyInstance:
    Type: 'AWS::EC2::Instance'
    Metadata:
      'AWS::CloudFormation::Init':
        configSets:
          InstallAndRun:
            - Install
            - Run
        Install:
          packages:
            yum:
              awscli: []
        Run:
          commands:
            01_swap_environment:
              command: >
                aws elasticbeanstalk swap-environment-cnames --source-environment-name my-app-v1
                --destination-environment-name my-app-v2
    Properties:
      InstanceType: t2.micro
      KeyName: my-key-pair
      ImageId: ami-0abcdef1234567890
      IamInstanceProfile: MyInstanceProfile

In this script, the CloudFormation AWS::CloudFormation::Init metadata is used to install the AWS CLI on an EC2 instance and then execute the aws elasticbeanstalk swap-environment-cnames command to swap the CNAMEs of two Elastic Beanstalk environments.

Related Reading

Top 40 AWS DevOps Interview Questions and Answers (2023 Update)

37. Can you explain AWS CloudFormation Stack Import/Export? (Stack Import/Export, Advanced Usage)

The AWS CloudFormation Stack Import/Export feature allows you to manage cross-stack references across different stacks. You can create an output value in one stack (export) and then import this output value in another stack.

The Export field in the Output section of a CloudFormation template specifies the value to export:

Outputs:
  MyBucketName:
    Description: The name of an S3 bucket
    Value: !Ref MyS3Bucket
    Export:
      Name: My-exported-bucket-name

Then, in another stack, you can use the !ImportValue function to import this exported value:

Resources:
  MyS3BucketPolicy:
    Type: 'AWS::S3::BucketPolicy'
    Properties:
      Bucket: !ImportValue My-exported-bucket-name
      ...

This allows you to share resources between stacks and re-use configurations, thus promoting resource efficiency and reducing duplication.

Understanding Terraform Workspace can provide more insight into similar management of environments in Terraform.

38. How can you use AWS CloudFormation in conjunction with AWS Service Catalog? (Service Catalog, Advanced Usage)

AWS Service Catalog allows organizations to create and manage catalogs of IT services approved for use on AWS. You can create a product in AWS Service Catalog using a CloudFormation template, which defines the AWS resources to be provisioned.

After the AWS Service Catalog product (CloudFormation template) is created, users with the necessary permissions can launch it, and a CloudFormation stack will be created accordingly. This stack manages the resources defined in the product’s CloudFormation template.

By using AWS Service Catalog and AWS CloudFormation together, you can standardize your infrastructure across your organization and simplify the provisioning process, while ensuring compliance and best practices are adhered to.

39. What is the AWS CloudFormation Stack Protection? (Stack Protection, Security)

Stack protection in AWS CloudFormation is a feature that prevents a stack from being accidentally deleted. When you enable termination protection for a stack, CloudFormation prevents the stack from being accidentally deleted. Anyone who attempts to delete a stack with termination protection enabled will encounter an error.

It is a good practice to enable stack protection, particularly for stacks that represent resources that are critical for your application or business. This ensures that these important stacks are not inadvertently deleted, thus enhancing the security and stability of your applications.

Here is how you can enable the stack protection in a CloudFormation template:

AWSTemplateFormatVersion: 2010-09-09
Resources:
  MyProtectedStack:
    Type: 'AWS::CloudFormation::Stack'
    Properties:
      TemplateURL: https://s3.amazonaws.com/cloudformation-templates-us-east-1/WordPress_Single_Instance.template
      TimeoutInMinutes: '60'
      EnableTerminationProtection: true

In this example, the EnableTerminationProtection property is set to true, indicating that the stack cannot be deleted until this protection is explicitly removed.

For more information on securing AWS resources, refer to our article on AWS EC2 Security: Security Group Facts.

40. How does AWS CloudFormation integrate with other DevOps tools? (DevOps, Integration, Advanced Usage)

AWS CloudFormation is designed to work seamlessly with other AWS services and popular DevOps tools. It provides the infrastructure needed for the continuous integration and continuous delivery (CI/CD) of applications and infrastructure.

  1. AWS CodePipeline: AWS CloudFormation can be used with AWS CodePipeline to model and automate the release process for your application.
  2. AWS CodeDeploy: AWS CloudFormation can be used to create AWS resources required by AWS CodeDeploy for application deployment.
  3. Jenkins: AWS provides plugins for Jenkins. One such plugin is AWS CloudFormation Plugin for Jenkins which allows Jenkins jobs to create or delete stacks using AWS CloudFormation.
  4. Chef, Puppet: Configuration management tools such as Chef and Puppet can be used with AWS CloudFormation to handle software and configurations on the created infrastructure.
  5. GitHub: Developers can store their AWS CloudFormation templates in a GitHub repository and version control them like any other source code.

For more details on how AWS CloudFormation fits into a DevOps workflow, you can check our article on Top Cloud Automation Tools.