Cross-stack references

When using the layered cake approach, it's very common to want to use outputs from one stack as inputs in another stack. For example, you may create a VPC in one stack and require its VPC ID when creating resources in another.

For a long time, one needed to provide some glue around stack creation to pass output between stacks. AWS recently introduced cross-stack references, which provide a more native way of doing this.

You can now export one or more outputs from your stack. This makes those outputs available to other stacks. Note that the name of this value needs to be unique, so it's probably a good idea to include the CloudFormation stack name in the name you're exporting to achieve this.

Once a value is exported, it becomes available to be imported in another stack using the Fn::ImportValue function—very handy!