Updating and deleting stacks in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

What happens when you update an AWS CloudFormation stack with a template that removes a resource?

You have an existing CloudFormation stack with several resources. You update the stack by uploading a new template that no longer includes one of the original resources. What is the expected behavior?

A The resource is deleted from the stack and removed from your AWS account.

B The resource remains unchanged in your AWS account but is no longer managed by the stack.

C The update fails with an error because resources cannot be removed from a stack.

D The resource is stopped but not deleted, and remains in your AWS account.

💡 Hint

Think about how CloudFormation manages resources when they are removed from the template.

When a resource is removed from a CloudFormation template during an update, CloudFormation deletes that resource from the stack and your AWS account, unless you have specified a deletion policy to retain it.

❓ Architecture

intermediate

Which AWS CloudFormation stack deletion policy prevents resource deletion when the stack is deleted?

You want to delete a CloudFormation stack but keep certain resources intact in your AWS account. Which deletion policy should you apply to those resources?

A Protect

B Snapshot

C Delete

D Retain

💡 Hint

Consider which policy tells CloudFormation to keep the resource even if the stack is deleted.

The 'Retain' deletion policy tells CloudFormation to keep the resource in your AWS account when the stack is deleted. 'Snapshot' creates a backup before deletion, 'Delete' removes the resource, and 'Protect' is not a valid deletion policy.

❓ security

advanced

What IAM permission is required to delete an AWS CloudFormation stack?

To delete a CloudFormation stack, which IAM permission must a user have?

A cloudformation:TerminateStack

B cloudformation:DeleteStack

C cloudformation:RemoveStack

D cloudformation:DestroyStack

💡 Hint

Check the exact AWS IAM action name for deleting stacks.

The correct IAM permission to delete a CloudFormation stack is 'cloudformation:DeleteStack'. The other options are not valid IAM actions.

✅ Best Practice

advanced

What is the recommended approach to update a CloudFormation stack with minimal downtime?

You need to update a CloudFormation stack that runs a web application. Which approach minimizes downtime during the update?

A Delete the stack and create a new one with the updated template immediately.

B Manually update resources outside CloudFormation to avoid stack updates.

C Use Change Sets to preview changes and update the stack during low traffic periods.

D Update the stack directly without previewing changes to speed up deployment.

💡 Hint

Think about how to safely apply changes with visibility before execution.

Using Change Sets allows you to preview the impact of changes before applying them, reducing the risk of downtime. Deleting the stack causes downtime, updating without preview risks errors, and manual updates break stack management.

🧠 Conceptual

expert

What is the effect of setting the 'DeletionPolicy' attribute to 'Snapshot' on an Amazon RDS instance in a CloudFormation stack when the stack is deleted?

You have an Amazon RDS instance defined in a CloudFormation stack with the 'DeletionPolicy' attribute set to 'Snapshot'. What happens to the RDS instance when you delete the stack?

A CloudFormation creates a snapshot of the RDS instance before deleting it.

B The RDS instance is deleted immediately without any snapshot.

C The RDS instance is retained and not deleted or snapshotted.

D The stack deletion fails with an error due to the snapshot policy.

💡 Hint

Consider what the 'Snapshot' deletion policy does for stateful resources.

Setting 'DeletionPolicy' to 'Snapshot' causes CloudFormation to create a snapshot of the resource before deleting it, preserving data. The resource is then deleted. 'Retain' would keep the resource, and deletion does not fail due to this policy.

Practice

1. What is the primary purpose of the update-stack command in AWS CloudFormation?

easy

A. To create a new stack from a template

B. To safely change existing cloud resources managed by a stack

C. To delete all resources created by a stack

D. To list all stacks in your AWS account

Solution

1. Step 1: Understand the role of update-stack

   The update-stack command is used to modify resources that are already managed by an existing CloudFormation stack.

2. Step 2: Differentiate from other commands

   Unlike delete-stack which removes resources, update-stack changes them safely without deleting the stack.

3. Final Answer:

   To safely change existing cloud resources managed by a stack -> Option B

4. Quick Check:

   update-stack = change resources safely [OK]

Hint: Update-stack changes resources; delete-stack removes them [OK]

Common Mistakes:

• Confusing update-stack with delete-stack
• Thinking update-stack creates new stacks
• Assuming update-stack lists stacks

2. Which AWS CLI command syntax correctly deletes a stack named MyAppStack?

easy

A. aws cloudformation delete-stack --stack-name MyAppStack

B. aws cloudformation update-stack --stack-name MyAppStack

C. aws cloudformation remove-stack --name MyAppStack

D. aws cloudformation destroy-stack --stack MyAppStack

Solution

1. Step 1: Identify the correct delete command

   The correct AWS CLI command to delete a stack is delete-stack with the parameter --stack-name.

2. Step 2: Verify syntax correctness

   aws cloudformation delete-stack --stack-name MyAppStack uses the exact syntax: aws cloudformation delete-stack --stack-name MyAppStack, which is valid and deployable.

3. Final Answer:

   aws cloudformation delete-stack --stack-name MyAppStack -> Option A

4. Quick Check:

   delete-stack + --stack-name = correct syntax [OK]

Hint: Delete stacks with 'delete-stack' and '--stack-name' [OK]

Common Mistakes:

• Using update-stack instead of delete-stack
• Wrong parameter names like --name or --stack
• Using non-existent commands like remove-stack or destroy-stack

3. Given this AWS CLI command sequence:

aws cloudformation update-stack --stack-name TestStack --template-body file://template.json
aws cloudformation describe-stacks --stack-name TestStack

What is the expected behavior after running these commands?

medium

A. The stack TestStack is updated with the new template, and its status is shown

B. The stack TestStack is deleted, and no status is returned

C. A new stack named TestStack is created, and its details are displayed

D. The command fails because update-stack cannot be followed by describe-stacks

Solution

1. Step 1: Understand update-stack effect

   The update-stack command modifies the existing stack named TestStack using the provided template.

2. Step 2: Describe-stacks shows current stack status

   The describe-stacks command retrieves details about TestStack, including its updated status.

3. Final Answer:

   The stack TestStack is updated with the new template, and its status is shown -> Option A

4. Quick Check:

   update-stack changes stack + describe-stacks shows status [OK]

Hint: Update then describe shows updated stack status [OK]

Common Mistakes:

• Thinking update-stack deletes the stack
• Assuming describe-stacks creates a new stack
• Believing update-stack and describe-stacks cannot be used sequentially

4. You run aws cloudformation update-stack --stack-name ProdStack --template-body file://newtemplate.json but get an error saying the stack is in UPDATE_IN_PROGRESS state. What should you do to fix this?

medium

A. Ignore the error and rerun update-stack multiple times

B. Run delete-stack immediately to remove the stack

C. Change the stack name and try update-stack again

D. Wait for the current update to finish before running update-stack again

Solution

1. Step 1: Understand stack states during update

   When a stack is in UPDATE_IN_PROGRESS, it means an update is already running and must complete before another update starts.

2. Step 2: Choose the correct action

   Waiting for the current update to finish avoids conflicts and errors. Deleting or renaming the stack is unnecessary and may cause data loss or confusion.

3. Final Answer:

   Wait for the current update to finish before running update-stack again -> Option D

4. Quick Check:

   UPDATE_IN_PROGRESS means wait before next update [OK]

Hint: Wait for update to finish before next update [OK]

Common Mistakes:

• Trying to delete stack during update
• Renaming stack instead of waiting
• Ignoring error and retrying immediately

5. You want to update a stack but also ensure that if the update fails, the stack rolls back to its previous state automatically. Which AWS CloudFormation option should you avoid using with update-stack to achieve this?

hard

A. --rollback-configuration

B. --no-rollback

C. --disable-rollback

D. --enable-rollback

Solution

1. Step 1: Understand rollback behavior in update-stack

   By default, CloudFormation rolls back stack updates on failure. The --disable-rollback option disables this behavior.

2. Step 2: Identify the correct option to keep rollback enabled

   To ensure rollback happens automatically on failure, you should NOT disable rollback. Therefore, do not use --disable-rollback. The default behavior is rollback enabled, so omit this option or explicitly avoid disabling rollback.

3. Step 3: Analyze options

   --rollback-configuration is for configuring alarms, --enable-rollback and --no-rollback are not valid AWS CLI options.

4. Final Answer:

   --disable-rollback disables rollback; omit it to keep rollback enabled -> Option C

5. Quick Check:

   Omit --disable-rollback to keep rollback on failure [OK]

Hint: Do not use --disable-rollback to keep rollback active [OK]

Common Mistakes:

• Using non-existent --enable-rollback option
• Confusing disable-rollback disables rollback
• Assuming rollback is off by default