Simplify dependency management for applets

[eladb]

When trying to use applets in 0.18.1 via a globally installed toolkit, you will get the following error:

Error: The child XXX of Program must be a Stack

This is because when the toolkit is globally installed, the copy of @aws-cdk/cdk (which defines Stack) is different than the one installed in the local node_modules. In JavaScript, instanceof is based on constructor object equality and they have to be the exact same copy in order to align.

Reported by @clareliguori

[eladb]

A workaround is to use the toolkit from a local install instead of a global install. As long as versions match, npm would de-dup the @aws-cdk/cdk module and Stack will be Stack.

For example, here is how to use the Fargate Service Applet:

$ mkdir fargate-service
$ npm i aws-cdk @aws-cdk/aws-ecs # notice that we install the toolkit locally here
$ cat > my-service.yaml <<HERE
applets:
  LoadBalancedFargateService:
    type: @aws-cdk/aws-ecs:LoadBalancedFargateServiceApplet
    properties:
      image: 'amazon/amazon-ecs-sample'
      cpu: "2048"
      memoryMiB: "1024"

HERE
$ npx cdk -a my-service.yaml synth # notice we use "npx" to invoke the cdk from the local install

[eladb]

There are a few things here to take care of:

• Stop using instanceof
• Maybe when using applets, the dependency closure should be managed by the toolkit. Would be nice if I didn't even have to install @aws-cdk/aws-ecs (but then, we might need a way to specify semver requirements). If we don't do that, we should get the user to install @aws-cdk/applet-js and use the local one and not install it globally
• The fact that the toolkit takes a dependency on the CDK framework is not a good idea in general

[rix0rrr]

The fact that the toolkit takes a dependency on the CDK framework is not a good idea in general.

True.

But the alternative is having to make a package.json and npm installing in a directory which is supposed to only contain a YAML file, which seems suboptimal as well. I was talking @SoManyHs through how to set up an applet and I couldn't in good conscience justify all the steps.

• Write your YAML (should be the one and only step)
• Write a package.json
• Install @aws-cdk/applets-js and @aws-cdk/aws-ecs.
• Create a cdk.json with the following in it:

{
  "app": "node_modules/.bin/cdk-applet-js template.yml"
}

• Finally you get to run cdk deploy

The single cdk.json makes it impossible to have multiple applet files in the same directory and access them easily (Yes, we can have multiple stacks in one file, but I think there's value in organizing into files).

We need to simplify this process.

[eladb]

I agree that we need to simplify but I think we should think of the end-to-end experience. If we really want only a .yaml file to be needed, then all dependencies should be implicitly managed somehow, which also means we need to be able to define version requirements in the applet, and we need to figure out how to cache those dependencies so that subsequent invocations won't need to install everything every time.