Can't use cache_nodes output of aws_elasticache_cluster as a list

[brikis98]

Terraform Version

Terraform v0.7.3

Affected Resource(s)

• aws_elasticache_cluster

Terraform Configuration Files

resource "aws_elasticache_cluster" "memcached" {
  cluster_id = "foo"
  engine = "memcached"

  num_cache_nodes = 3
  node_type = "cache.t2.micro"
}

output "node_addresses" {
  value = ["${aws_elasticache_cluster.memcached.cache_nodes.*.address}"]
}

Expected Behavior

I get a list of 3 node addresses as an output.

Actual Behavior

I get nothing.

Steps to Reproduce

1. terraform apply

Important Factoids

If I change the output to a hard-coded item, it works correctly:

output "node_addresses" {
  value = "${aws_elasticache_cluster.memcached.cache_nodes.0.address}"
}

But this obviously doesn't work if the number of cache nodes is controlled by a variable. I tried to work around it in various ways, but it looks like cache_nodes isn't a proper list. All the typical list operations, like join, split, and element do not work on it. Therefore, I can't find any way to dynamically return a list of node addresses or ids or to pass them onto another module (e.g. a module that adds CloudWatch alarms to each node).

References

• aws_elasticache_replication_group does not provide cache_nodes output #8788

[mattsoftware]

I am seeing this too, trying to get a list of addresses however ${join(",", aws_elasticache_cluster.main.cache_nodes.*.address)} appears to be empty

[calvinfo]

+1 we also had this problem.

The current workaround for us is using a template file, but it relies on the underlying format of AWS configuration endpoint in conjunction with the individual node endpoints which is pretty hacky:

resource "aws_elasticache_cluster" "main" {
  cluster_id = "${var.cluster_id}"
  engine = "${var.engine}"
  ...
}

resource "template_file" "hosts" {
  count = "${var.node_count}"
  template = "${file("${path.module}/template.tpl")}"

  vars {
    endpoint = "${aws_elasticache_cluster.main.configuration_endpoint}"
    count = "${format("%04d", count.index + 1)}"
  }
}

/**
 * Outputs.
 */

output "node_endpoints" { value = "${join(",", template_file.hosts.*.rendered)}" }
output "endpoint" { value = "${aws_elasticache_cluster.main.configuration_endpoint}" }

And then the template file:

${replace("${endpoint}", "cfg", "${count}")}

[mitchellh]

This is a dup of #9080 it looks like, or even potentially #8695 which was just fixed.

[calvinfo]

Woot, thank you! 🎉

[achille-roussel]

@mitchellh we're still seeing the problem occur, should we re-open?

[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.