[FEATURE]: Support runtime outputs for Helm chart values

Feature Request

Background / Motivation

Today, we use a jungle of bash scripts to pass Cloudformation and Terraform outputs to our Helm charts. Typically, these values are indeterminate until deploy time (e.g. AWS RDS endpoint URLs). We were looking to use Garden to streamline handling these outputs.

What should the user be able to do?

A Garden user should be able to reference runtime outputs in their Helm chart values. e.g.

Terraform that creates an SNS topic

----
kind: Module
type: terraform
name: tf-infra

---
kind: Module
type: helm
.
.
.
serviceResource:
    containerModule: docker-image
dependencies:
    - tf-infra
values:
    microservice:
        appConfig:
            environment:
                SNS_TOPIC_ARN: ${runtime.services.tf-infra.outputs.sns_topic_arn}
              # or
              # SNS_TOPIC_ARN: ${providers.terraform.outputs.sns_topic_arn}
        image:
            repository: ${modules.docker-image.outputs.deployment-image-name}
            tag: ${modules.docker-image.version}

Why do they want to do this? What problem does it solve?

It allows runtime outputs from Terraform (or other modules such as exec) to be resolvable at deploy time.

Suggested Implementation(s)

• Allow the Helm module values: stanza to resolve runtime outputs.
• Add an additional setValues: stanza to the Helm module to allow runtime variables to be passed to Helm via --set at deploy time.

How important is this feature for you/your team?

🥀 Crucial, Garden is unusable for us without it

We want to take a machete to our jungle of bash. Please help! 😃

[edvald]

Just for a bit of context, the reason for the current implementation was to allow plugins like conftest-kubernetes to validate rendered charts ahead of deployment. So it’s not quite trivial to address, but it’s worth figuring out for sure.

[edvald]

Ok, this should be ready in our next release.