cloudformation.md

CloudFormation

In-memory CloudFormation implementation supporting stack lifecycle management, resource introspection, cross-stack exports, and change sets.

Supported Operations

Operation	Description
CreateStack	Create a new stack from a template
UpdateStack	Update an existing stack
DeleteStack	Delete a stack and its resources
DescribeStacks	Get stack details and outputs
ListStacks	List stacks with optional status filter
DescribeStackEvents	Get the event history for a stack
DescribeStackResource	Get details of a specific resource by logical ID
ListStackResources	Paginated list of all resources in a stack
DescribeStackResources	Describe all resources in a stack
ListExports	List all exported output values across stacks
ListImports	List stacks that import a specific export
CreateChangeSet	Create a change set to preview stack changes
DescribeChangeSet	Get change set details
ExecuteChangeSet	Apply a change set to the stack
DeleteChangeSet	Delete a change set
ListChangeSets	List change sets for a stack
GetTemplate	Get the template body for a stack

Template Intrinsics

Intrinsic	Description
Ref	Reference a parameter or resource physical ID
Fn::Sub	String substitution with ${Variable} placeholders
Fn::Join	Join a list of values with a delimiter
Fn::Split	Split a string by delimiter
Fn::Select	Select a value from a list by index
Fn::FindInMap	Look up a value in the Mappings section
Fn::If	Conditional value selection based on a Conditions entry
Fn::Equals	Equality comparison for use in Conditions
Fn::And / Fn::Or / Fn::Not	Boolean operators for Conditions
Fn::ImportValue	Import a cross-stack export value

Cross-Stack Exports

When a stack output declares an Export.Name, the value becomes available to other stacks via Fn::ImportValue:

Outputs:
  VpcId:
    Value: !Ref MyVPC
    Export:
      Name: shared-vpc-id

{
  "Resources": {
    "MyInstance": {
      "Type": "AWS::EC2::Instance",
      "Properties": {
        "SubnetId": {"Fn::ImportValue": "shared-vpc-id"}
      }
    }
  }
}

Exports are removed automatically when the owning stack is deleted.

AWS CLI Examples

# Create a stack
aws --endpoint-url http://localhost:8000 cloudformation create-stack \
    --stack-name my-stack \
    --template-body '{"AWSTemplateFormatVersion":"2010-09-09","Resources":{"MyBucket":{"Type":"AWS::S3::Bucket"}}}'

# Describe stacks
aws --endpoint-url http://localhost:8000 cloudformation describe-stacks \
    --stack-name my-stack

# Describe a specific resource in a stack
aws --endpoint-url http://localhost:8000 cloudformation describe-stack-resource \
    --stack-name my-stack \
    --logical-resource-id MyBucket

# List all resources in a stack
aws --endpoint-url http://localhost:8000 cloudformation list-stack-resources \
    --stack-name my-stack

# Describe all resources in a stack
aws --endpoint-url http://localhost:8000 cloudformation describe-stack-resources \
    --stack-name my-stack

# List all cross-stack exports
aws --endpoint-url http://localhost:8000 cloudformation list-exports

# List stacks that import a specific export
aws --endpoint-url http://localhost:8000 cloudformation list-imports \
    --export-name shared-vpc-id

# Create a change set
aws --endpoint-url http://localhost:8000 cloudformation create-change-set \
    --stack-name my-stack \
    --change-set-name my-changes \
    --template-body '{"AWSTemplateFormatVersion":"2010-09-09","Resources":{"MyBucket":{"Type":"AWS::S3::Bucket"},"MyQueue":{"Type":"AWS::SQS::Queue"}}}'

# Execute the change set
aws --endpoint-url http://localhost:8000 cloudformation execute-change-set \
    --stack-name my-stack \
    --change-set-name my-changes

# Get stack events
aws --endpoint-url http://localhost:8000 cloudformation describe-stack-events \
    --stack-name my-stack

# Delete a stack
aws --endpoint-url http://localhost:8000 cloudformation delete-stack \
    --stack-name my-stack

Known Limitations

• CloudFormation StackSets and nested stacks are not supported.
• Custom resources (Lambda-backed) are not invoked.
• Stack rollback on failure is simulated but resources are not actually rolled back.