Add support for Terraform Variables

[skorfmann]

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Description

It would be good to support Terraform variables as first class construct. This will be helpful for hybrid approaches and for creating a Terraform module from constructs.

[vmarchaud]

I'm not sure i understand correctly, but does this issue means that we can't use terraform variable right now using CDK ?

[skorfmann]

I'm not sure i understand correctly, but does this issue means that we can't use terraform variable right now using CDK ?

There's no explicit construct to support variables at the moment. Variables still can be supported via escape hatches. See this for a full example.

Here an excerpt:

stack.addOverride('variable', {
  tags: {
    description: "Tags for the instance",
    type: "map(string)"
  },
  instance_type: {
    description: "Instance type",
    type: "string"
  }
})

[vmarchaud]

@skorfmann Thanks for the quick answer, i believe adding this into the readme would be helpful to people looking to migrate to CDK :)

[skorfmann]

@skorfmann Thanks for the quick answer, i believe adding this into the readme would be helpful to people looking to migrate to CDK :)

No, worries. Adding this to the docs would make sense, yes 👍

Out of curiosity, could you elaborate on your use-case for variables?

[vmarchaud]

Sure, here is some options (in TS) on the infrastructure i'm trying to migrate:

type InfrastructureToolingOptions = {
  environment: string
  gcp_credentials: string
  sva_dns: string
  project: string
  region: string

  gke: {
    pool_min: number
    pool_max: number
    pool_type: number
    version: string,
    nodes_cidr: string
    pods_cidr: string
    master_cidr: string
  }
}

There obviously some default that i'm setting in the code directly, but i like to be able to override them on the UI (and allows for non-ops to edit them too). For some variables which are secret like gcp_credentials or sva_dns they are all set inside TF Cloud as "secret"

[skorfmann]

Thanks, that's quite interesting. I had primarily modules as a use-case for this in mind. Terraform Cloud looks certainly like another very compelling use-case for this /cc @anubhavmishra

@vmarchaud how do you approach the CDK in Terraform Cloud? Commit the synthesized JSON and use this a basis for the Terraform Cloud?

[vmarchaud]

Thanks, that's quite interesting. I had primarily modules as a use-case for this in mind.

Well after seeing your examples to use the variables, i believe making a module would be the easiest way to use them.

how do you approach the CDK in Terraform Cloud? Commit the synthesized JSON and use this a basis for the Terraform Cloud?

Well that's a unknown for me, from what i read i can use the RemoteState and the local apply, it should be able to read the variables on Terraform Cloud and apply them locally ?

EDIT: Worth to mention that this project (~30 resources) is quite small so its pretty much a playground to try make it works. I would like to migrate my main infrastructure (with ~200 resources) later on though

[jsteinich]

Personally I'm still split between converting variables to code/configuration files and keeping them around. We are using Terraform Atlantis, so I could add in a step to CDK synth, but that requires adding in the build dependencies.

Having variable support would be a nice stepping stone to convert existing infrastructure though.

[skorfmann]

EDIT: Worth to mention that this project (~30 resources) is quite small so its pretty much a playground to try make it works. I would like to migrate my main infrastructure (with ~200 resources) later on though

Yes, please be also aware that this project is still considered alpha with frequent (breaking) changes.

Well that's a unknown for me, from what i read i can use the RemoteState and the local apply, it should be able to read the variables on Terraform Cloud and apply them locally ?

I guess so, haven't used Terraform Cloud that much yet. The remote state is being worked on at the moment - see #241.

I thought you had Terraform Cloud hooked up to Github somehow, and it'd execute a deploy on your behalf.

[skorfmann]

Personally I'm still split between converting variables to code/configuration files and keeping them around. We are using Terraform Atlantis, so I could add in a step to CDK synth, but that requires adding in the build dependencies.

Not sure if I understand this correctly. If you wouldn't add a build step for the CDK, how would you ship it via Atlantis then?

[jsteinich]

Not sure if I understand this correctly. If you wouldn't add a build step for the CDK, how would you ship it via Atlantis then?

Just a question of whether Atlantis executes the step or something else does beforehand and passes along the synthesized JSON.

[Ivan-Razhnou1]

Hi Folks,
When do you expect this functionality to be available via npm?

[jsteinich]

When do you expect this functionality to be available via npm?

If you're using ts/js it should already be available using the @next version.

[jsteinich]

This was released in 0.0.18

[github-actions]

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