How to Use Imports and Catalogs in Stacks

Problem

As infrastructure grows, we end up with hundreds or thousands of settings for components and stack configurations. If we copy and paste these settings everywhere, it’s error-prone and not DRY. What we really want to do is to define a sane set of defaults and override those defaults when we need them to change.

Solution

tip

Use the import together with the catalog convention to write DRY configurations you can re-use any number of times.

Using a component catalog, you can define the default values for all instances of a component across your stacks.

It is also important to note that you can provide default values for multiple instances of a component in a single stack using the component inheritance pattern via the component attribute.

# stacks/catalog/s3/bucket.yaml
components:
  terraform:
    s3-bucket:
      vars:
        # By convention, leave the component disabled in the catalog configuration (you can enable each inherited components individually)
        enabled: false
        user_enabled: false
        acl: private
        grants: null
        versioning_enabled: true

info

The import works by deep merging all files in the order they are defined using the Mergo library.

Then inside of a stack configuration (uw2-dev for example), we can import the catalog/s3/bucket component configuration into our stack and use the s3-bucket component defined therein.

# stacks/uw2-dev.yaml
import:
  - catalog/s3/bucket

components:
  terraform:
    public-images:
      component: s3-bucket       # Inherit all the settings from the `s3-bucket` component
      vars:
        enabled: true            # Enable the component
        acl: public              # Override the ACL and make this a public bucket
        name: public-images      # Give it a unique name

    private-artifacts:
      component: s3-bucket       # Inherit all the settings from the `s3-bucket` component
      vars:
        enabled: true            # Enable the component
        name: private-artifacts  # Give it a unique name

    # ...

In the above example, we’re able to utilize the default settings provided via the s3-bucket base component from the catalog, while also creating multiple instances of the same component and providing our own overrides. This enables maximum reuse of global component configuration with minimal configuration.

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