CODEWITHSUNDEEP
interpolationterraform
Matt Canty
Matt Canty

Reputation: 2465

Converting resource to string list with Terraform interpolation

Given a .tfvars containing:

environment = "dev"
web_servers = ["192.168.0.1","192.168.0.2"]

and a node resource like:

resource "node" "web_nodes" {
  count = "${length(var.web_servers)}"
  name = "${var.environment}_web_${count.index}"
  address = "${element(var.web_servers, count.index)}"
}

I want to express the following dynamically:

resource "pool" "homepage_pool" {
  name = "homepage_${var.environment}"
  nodes = [
    "dev_web_0:443",
    "dev_web_1:443"
  ]
}

with a plan output like:

nodes.2387117855: "" => "dev_web_1:443"
nodes.3005787823: "" => "dev_web_0:443"

I think that pool.nodes should be generated using something like formatlist() or join() or a combination of the 2. Struggling to find decent examples.

The closest I can get results in a plan like:

nodes.467461356: "" => "\"/Common/preprod_web_0\","/Common/preprod_web_1\""

Upvotes: 3

Views: 5787

Answers (1)

Martin Atkins
Martin Atkins

Reputation: 74064

The formatlist function can be used in conjunction with the "splat" operator to get the result you need here.

The "splat" operator allows you to concisely create a list from a given attribute of a set of counted resource instances. Your example here it seems that you want to use the node name and a hard-coded port 443, in which case this can be expressed as follows:

resource "pool" "homepage_pool" {
  name = "homepage_${var.environment}"
  nodes = "${formatlist("%s:443", node.web_nodes.*.name)}"
}

The notation node.web_nodes.*.name means to take the name attribute of each of the instances created under the name node.web_nodes and produce a list of strings from them. formatlist then applies the given format to each element of the list in turn, appending the :443 port suffix.

Upvotes: 5

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