revisit prefix handling

[juliocc]

Handling of the prefix variable is inconsistent across modules. For example project doesn't allow "" but gcs does.

Agree on a single pattern and use it in all modules.

[skalolazka]

To summarize the proper usage:

1. Conditional in locals to detect null and empty string
2. Default null in variables.tf
   So the ideal way is, for example, in the iam-service-account module:
   prefix = var.prefix == null || var.prefix == "" ? "" : "${var.prefix}-"
   Is my understanding correct?

[juliocc]

I would prefer validating that prefix != "" and just handling the case when prefix == null

The local for iam-service-account would end up like this:

prefix = var.prefix == null ? "" : "${var.prefix}-"

@ludoo wdyt?

[ludoo]

I would prefer validating that prefix != "" and just handling the case when prefix == null

The local for iam-service-account would end up like this:

prefix = var.prefix == null ? "" : "${var.prefix}-"

@ludoo wdyt?

yes, absolutely. Validation in the variable for empty string, and test on null in locals.

[skalolazka]

Opened #967 for the blueprints.