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Best Practices

Guardian CDK codifies best practices as defined in the recommendations repo.

AWS CDK

AWS recommends best practices for developing and deploying cloud infrastructure with CDK.

Guardian CDK

Here are some recommendations for using the Guardian CDK library:

  • Use CI to run snapshot tests
  • Use CI to generate cloudformation files
  • Upload generated json files from cdk.out

Snapshot testing

Snapshot testing with Jest makes it easy to review any stack changes when developing locally and in PRs. This enables us to catch things early, creating a shorter feedback loop. npm run test-update/yarn test-update will update the snapshots. See the AWS docs on snapshot testing.

Mocking gu:cdk:version

The @guardian/cdk library follows Semantic Versioning.

GuCDK will add the gu:cdk:version tag to resources to aid usage tracking. This number changes with every version and as a result automatic version upgrade PRs (e.g. via Dependabot) will fail their snapshot tests. To reduce friction, GuCDK ships a mock that can be used with Jest, resulting in snapshots having a static value for this tag.

To use it, first, create jest.setup.js and add the global mock:

jest.mock("@guardian/cdk/lib/constants/tracking-tag");

Next, edit jest.config.js setting the setupFilesAfterEnv property:

module.exports = {
  setupFilesAfterEnv: ["./jest.setup.js"],
};

Finally, update your snapshots (jest -u).

The gu:cdk:version tag should now be:

{
  "Key": "gu:cdk:version",
  "PropagateAtLaunch": true,
  "Value": "TEST", // <-- would otherwise be the version number of @guardian/cdk in use
}

Note:

  • This mock only affects tests. The gu:cdk:version tag in the final template created from a cdk synth will have the correct value
  • This mock is automatically configured when using the GuCDK project generator

✨ With gu:cdk:version mocked, snapshot tests run during CI, you can feel confident about merging Dependabot PRs that bump @guardian/cdk once CI passes ✨.

Generating the cloudformation template

CI should generate files in the cdk.out directory (make sure to add this to .gitignore).

CDK will produce json files by default, one per stage. These should be wired into the riff-raff.yaml:

# ... other required properties
deployments:
  cloudformation:
    type: cloud-formation
    templateStagePaths:
      CODE: MyApp-CODE.template.json
      PROD: MyApp-PROD.template.json
    # ... other required properties