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@guardian/cdk - v34.0.0

General Usage for @guardian/cdk

๐Ÿ–ฅ Installation

This library can be installed from NPM.

npm install --save @guardian/cdk


yarn add @guardian/cdk

We recommend using TypeScript with @guardian/cdk as type safety is wonderful!

๐ŸŸ Patterns

Patterns are high level classes which compose a number of constructs to produce standard architectures.

For example, you should be able to get all the resources you need to deploy a new lambda function from one GuLambdaStack class.

Patterns should be your default entry point to this library and can be found here.

๐Ÿ— Constructs

Constructs are lower level classes which will create one or more resources to produce one element of a stack.

For example, the GuDatabaseInstance will create an RDS instance as well as a parameter group, if required. This library defines a number of constructs which are combined to create the higher level patterns.

If there is a pattern available for your use case, prefer to use that over composing constructs yourself. We welcome feedback and/or PRs to extend the functionality of patterns.

Where you need to do something outside currently available patterns, you can use the constructs to provide some level of abstraction. In this case, consider whether it's worth defining a pattern.

Using patterns and constructs

Patterns can be imported from the top level of the library:

import { GuScheduledLambda } from "@guardian/cdk";

While constructs must be imported from their construct directory:

import { GuAutoScalingGroup } from "@guardian/cdk/lib/constructs/autoscaling";

โ˜๏ธ AWS Library Versions

Any versions of the @aws-cdk libraries that you have installed in your project must be the same version as those used in the @guardian/cdk library.

๐Ÿชก Synthesising

The cdk synth command can be used to generate cloudformation from CDK definitions. This will, by default, generate JSON in the cdk.out directory.

We recommend using TypeScript with @guardian/cdk as type safety is wonderful!

This does, however require the use of ts-node to compile on the fly. This can be done in two ways:

  1. Setting the app property in the cdk.json configuration file
  2. Passing the app flag to cdk. For example cdk synth --app="ts-node ./bin/my-app.ts"

Synthesising as YAML

For apps with a single stack, the generated YAML will also be printed in the console. You can pipe this to disk:

cdk synth --app="ts-node ./bin/my-app.ts" > cloudformation.yaml

For app with multiple stacks, you can specify a stack to see the YAML output.

๐Ÿงช Testing

It is recommended to set up Jest snapshot testing for your stack and have the test run during CI.

Snapshot tests allow you to very quickly see the changes that will be made to the generated template. This is especially useful when upgrading the version of @guardian/cdk.

๐Ÿ†™ Upgrading

The @guardian/cdk library follows Semantic Versioning.

If you have snapshot testing set up and running in CI, you should feel comfortable updating to any patch or minor release. You can use dependabot to automate this.

By default, automatic version upgrade PRs will fail their snapshot tests. This is because @guardian/cdk adds a tracking tag (gu:cdk:version) to resources with the version number of the library.

To reduce friction, @guardian/cdk ships a mock that can be used with Jest, which results in snapshots having a static value for this tag.

๐Ÿƒ Mocking gu:cdk:version

We recommend setting up a global Jest mock for gu:cdk:version. This can be done with a few config changes.

First, create jest.setup.js and add the global mock:


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

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

Finally, update your snapshots. 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 only affects tests. The gu:cdk:version tag in the final template created from a cdk synth will have the correct value.

โœจ With gu:cdk:version mocked, snapshot tests run during CI and dependabot automatically raising PRs to update @guardian/cdk, once CI passes, you can confidently merge PRs to adopt the AWS best practices encoded in @guardian/cdk โœจ.

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