14. Nested Stacks

Nested stacks that are part of other stacks. They allow you to isolate repeated patterns common components, etc. These are considered best practice, and to update a nested stack, you always need to update the parent.

We can output values for others stacks inside the nested stack like this:

Outputs:
  SSHGroupId:
    Value: !Ref SSHSecGroup
    Description: A meaningful description

Then we have to create a resource of the type AWS::CloudFormation::Stack, so we first upload our last stack to a S3 bucket, copy its URL and create the resource like the following. More info in the docs.

Type: AWS::CloudFormation::Stack
Properties: 
  NotificationARNs: 
    - String
  Parameters: 
    Key : Value
  Tags: 
    - Tag
  TemplateURL: String
  TimeoutInMinutes: Integer

To update a nested stack, we need to update the parent. For this, we’ll need to update a new file to a S3 Bucket and change the URL for the new one or use a “version” of the same S3 object.

These are helpful when stacks have different lifecycles. We can use the Outputs Export and Fn::ImportValue for things like VPC Id, etc.

On the other hand, nested stacks are helpful when components must be reused.