Default value for map variables

[phrawzty]

Hello,

As suggested by @jdotpz in the google group it would be handy if map variables were able to have a default value. Example:

variable "ec2_type" {
    default = {
        stage = "r3.large"
        prod = "r3.2xlarge"
        * = "m3.medium"
    }
}

Such that:

## defined (actual behaviour)
$environment="stage"
${lookup(var.ec2_type, var.environment)} == "r3.large"

## catch all (proposed behaviour)
$environment = "foo"
${lookup(var.ec2_type, var.environment)} == "m3.medium"

Another possible extension would be to allow for differentiating between "catch-all" and "empty / undefined" - this should be debated first, however. 😏 :

variable "ec2_type" {
    default = {
        stage = "r3.large"
        prod = "r3.2xlarge"
        default = "m3.medium"
        none = "t1.micro"
    }
}

Such that:

## defined (actual behaviour)
$environment="stage"
${lookup(var.ec2_type, var.environment)} == "r3.large"

## catch all (proposed behaviour)
$environment = "foo"
${lookup(var.ec2_type, var.environment)} == "m3.medium"

## undef (possible behaviour)
${lookup(var.ec2_type, var.environment)} == "t1.micro"

[ryangraham]

I was just looking for something like this for selecting PV versus HVM AMIs by instance_type.

[phinze]

@ryangraham you might be interested in https://github.com/terraform-community-modules/tf_aws_virttype 😀

[gozer]

👍

[jfelixetcetera]

I'd find this incredibly handy, in either the form above, or as a third parameter to lookup as described in #1505.

[arshdeeptinna]

Isn't this functionality supported sine 0.7 in the following form?

lookup(var.amis, var.env, 'Default-AMI')

[jfelixetcetera]

Yes, it got implemented but many of the PRs asking for it were updated slowly. Here's another reference, demonstrating how you can use a * or default param in a map to achieve it (with the third param in lookup). Not quite as clean as an automatic fallback, but more explicit so maybe better.

[apparentlymart]

Hi all,

As @arshdeeptinna pointed out, the lookup function now has a third argument for specifying defaults. Terraform 0.7 added the first-class index operator like var.amis[var.env], which has been generalized for the forthcoming v0.12.0 release to work with any expression rather than just with variables, so from that v0.12.0 onwards the lookup function's primary purpose will be providing a fallback value, and the index operator should be used in all other cases.

Since there's already a solution for this, I'm going to close this out. Sorry for letting this sit here for so long.

[ghost]

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.

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