Terraform: Variable references within other variable declarations

[ckelner]

This may be a duplicate, if so I apologize, I did search for some similar issue first but came up empty.

I'd like to be able to perform variable references in other variable declarations, for example:

variable "project" {}
variable "front_end_name" {}
...
project = "grid-gor-staging"
front_end_name = "${var.project}-frontend-web"

Hopefully this makes sense. I tried a few variations to get it to work, but was unsuccessful and couldn't locate any documentation that referenced any logic similar to this.

[LeftyBC]

I'm working around this with concat() in some cases, but it's not very reliable, so would love to see interpolations in variables.

[npryce]

We've run into the same problem. Being unable to define variables with interpolations means lots of implicit coupling becomes hidden around our Terraform config.

Any idea when this will be addressed?

[igoratencompass]

+1 for this request

[chazu]

+1 for this please :bow:

[geovanisouza92]

+1

[alexsomesan]

+1

[igoratencompass]

More than a year in open state, is this so difficult to implement?

[FrederikNygaardSvendsen]

+1

[GMartinez-Sisti]

+1

[purpleidea]

More than a year in open state, is this so difficult to implement?

@igoratencompass If it's not so difficult, perhaps you could help by contributing a patch? That's sort of how this works...

[daveadams]

For me, the now several-months-old locals feature addressed this need entirely (https://www.terraform.io/docs/configuration/locals.html). Might it be time to close this issue?

[cpanato]

+1

[hernanc]

+1

[faithlinpaul]

+1

[apparentlymart]

Hi all! Sorry we missed this on a previous cleanup pass due to it using an outdated labeling scheme.

As @daveadams pointed out, Local Values are intended to address this use-case, separately from Input Variables which exist only to accept data from _outside_ the module.

The documentation page shows some examples of mixing variables and locals to provide default patterns that a caller can optionally override.

[steinybot]

I don't think local values address this completely.

I want to define an input variable where the default value will use another input variable unless it is defined itself.

[hashibot[bot]]

I'm going to lock this issue because it has been closed for _30 days_ ⏳. This helps our maintainers find and focus on the active issues.

If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.