Variable interpolation of a multiple instance resource

[Nalum]

I have the following aws_instance resource:

resource "aws_instance" "api" {
    ami = "${lookup(var.aws-amis, var.aws-region)}"
    instance_type = "${var.aws-instance-type}"
    ebs_optimized = true
    key_name = "${lookup(var.aws-keys, var.aws-region)}"

    security_groups = [
        "${aws_security_group.api.name}"
    ]

    tags = {
        Name = "API"
    }

    provisioner "local-exec" {
        command = "echo ${aws_instance.api.*.public_ip} >> public_ips"
    }

    count = 2
}

When run this resource is creating the public_ips file with the following content:

54.204.171.92
54.204.171.92B780FFEC-B661-4EB8-9236-A01737AD98B654.146.132.10

As you can see the IP of the first instance is duplicated and there is, what I assume to be, a Terraform ID followed by the IP of the second instance.

This is causing issues for me provisioning the machines using chef. Am I doing this correctly or should I be doing it another way?

[svanharmelen]

@Nalum I assume you want to use the count.index here to get only a single IP for a specific resource right? I think (not tested) you could try something like this: ${concat("aws_instance.api.", count.index, ".public_ip")}"?

The UUID in the second string you get, is actually an internally used UUID that should not be exposed/shown. I think that could be considered a bug, but it's not really related to your issue.

[Nalum]

@svanharmelen I've just tried to use that as follows:

${concat("aws_instance.api.", count.index, ".public_ip")}

And

${${concat("aws_instance.api.", count.index, ".public_ip")}}

The first one added the following to the file:

aws_instance.api.0.public_ip
aws_instance.api.1.public_ip

And the second one gave the following error:

aws_instance.api.0 (local-exec): Executing: /bin/sh -c "echo ${aws_instance.api.0.public_ip} >> public_ips"
aws_instance.api.0 (local-exec): /bin/sh: 1: Bad substitution

I also tried this:

${lookup(concat("aws_instance.api.", count.index), "public_ip")}

But got the following error:

* lookup(concat("aws_instance.api.", count.index), "public_ip"): lookup in 'aws_instance.api.1' failed to find 'public_ip'

[svanharmelen]

@Nalum after digging some deeper I noticed this isn't supported yet... Sorry for the confusion! So this has to be added as a feature to TF and currently cannot be done...

[armon]

The way to do this would be with "${element(aws_instance.api.*.public_ip, count.index}".
The element() function is new, but will be part of the latest release!

[svanharmelen]

@armon you beat me to it 😉 Was looking to find any open issues and just found that PR #554 already fixed this and is merged into master...

[Nalum]

@armon @svanharmelen Thanks guys. Do you know when this release is due?

[svanharmelen]

@Nalum version 0.3.5 is just released and contains the new Element() function. See the CHANGELOG for more info...

[Nalum]

@svanharmelen brilliant, thank you very much.