provider/aws aws_elasticache_cluster: cache_nodes list behaves strangely

[tothandras]

Terraform Version

Terraform v0.9.1

Affected Resource(s)

• provider/aws:
  • aws_elasticache_cluster

Terraform Configuration Files

The relevant parts:

# this works:
output "nodes" {
  value = ["${format("%s:%s", aws_elasticache_cluster.redis.cache_nodes.0.address, aws_elasticache_cluster.redis.cache_nodes.0.port)}"]
}

# this doesn't:
# output "nodes" {
#  value = ["${formatlist("%s:%s", aws_elasticache_cluster.redis.cache_nodes.*.address, aws_elasticache_cluster.redis.cache_nodes.*.port)}"]
# }

Also:

At column 3, line 1: element: argument 1 should be type list, got type string in:

${element(aws_elasticache_cluster.redis.cache_nodes.*.port, count.index)}

Steps to Reproduce

1. terraform apply

[tothandras]

@grubernaut I'd like to contribute with a PR by fixing this bug. Can you help me where I should look for the root issue? Could it come from the resource itself or somewhere else?

[joelhandwell]

@jbardin Related with #10657 ?

[teamterraform]

Hi @tothandras! Sorry for the long silence here.

This looks like a symptom of a known limitation in Terraform 0.11 and earlier where any list containing an unknown value would itself become an unknown value and no longer be accepted as a list by the type checker.

Terraform 0.12 has addressed that by improving the representation of unknown values so that a list can contain a mixture of known and unknown elements and so that unknown values still track type information.

The handling of these language features was completely rewritten for Terraform 0.12, so if anyone is still seeing problems related to these features we'd ask that you open a new issue so we can capture (via the issue template) information about the bug as it relates to the new implementation. Thanks for reporting this, and sorry again it took so long to respond to it.

[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.

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.