Updating and deleting stacks in AWS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a CloudFormation stack update?

A stack update is the process of changing the resources or settings in an existing CloudFormation stack to match a new template or parameters.

beginner

What happens if a stack update fails?

If a stack update fails, CloudFormation rolls back the changes to keep the stack in its previous stable state.

beginner

How do you delete a CloudFormation stack?

You delete a stack by telling CloudFormation to remove all the resources it created for that stack, cleaning up everything automatically.

intermediate

What should you check before deleting a stack?

Check if any resources are still in use or have dependencies outside the stack to avoid breaking other systems.

intermediate

Can you update a stack to remove resources?

Yes, by modifying the template to remove resources and then updating the stack, CloudFormation deletes those resources during the update.

What does CloudFormation do if a stack update fails?

A Rolls back to the previous stack state

B Leaves the stack partially updated

C Deletes the stack automatically

D Ignores the failure and continues

CloudFormation rolls back the stack to its previous stable state to avoid partial updates.

Which action deletes all resources created by a CloudFormation stack?

A Pausing the stack

B Updating the stack

C Creating a new stack

D Deleting the stack

Deleting the stack removes all resources created by that stack.

How can you remove a resource from a stack?

A Update the stack with a template that excludes the resource

B Delete the resource manually

C Pause the stack

D Rename the resource

Updating the stack with a new template that removes the resource causes CloudFormation to delete it.

Before deleting a stack, what should you verify?

A That the stack is paused

B That no resources are used elsewhere

C That the stack is updated

D That the stack has no outputs

Ensure no resources are in use outside the stack to prevent breaking dependencies.

What is the main benefit of stack updates?

A Creating new resources only

B Deleting the stack automatically

C Changing existing resources without deleting the stack

D Backing up stack data

Stack updates allow changing resources without deleting the entire stack.

Explain the process and safety mechanisms involved when updating a CloudFormation stack.

Think about how CloudFormation keeps your resources safe during changes.

Describe the steps and considerations before deleting a CloudFormation stack.

Deleting a stack is like cleaning up a project; make sure nothing important is still connected.

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