Variable interpolation of a multiple instance resource

[Nalum]

I'm creating this as a separate issue to #633.

When using the following syntax ${aws_instance.api.*.public_ip} in the local-exec provisioner it will create the following string when it's running for the second instance:

54.166.168.91
54.166.147.56B780FFEC-B661-4EB8-9236-A01737AD98B654.166.168.91

The resource is as follows:

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
}

[armon]

Hmm this is interesting... I think this should cause an error. This means that every aws_instance.api depends on every other aws_instance.api. There is no sane way for TF to handle that dependency AFAIK.

[Nalum]

Just to make sure it is clear, as reading over it again it may not have been.

The second instance creates this string: 54.166.147.56B780FFEC-B661-4EB8-9236-A01737AD98B654.166.168.91

[mitchellh]

Theoretically this is possible, but not without major internal refactoring of Terraform. In the short term, I believe we should at least validate this as an error, and I'll make this the goal of this issue.

[MerlinDMC]

For me the problem is more that the interpolation delimiter (

terraform/config/interpolate_walk.go

Line 15 in 36f225d

const InterpSplitDelim = `B780FFEC-B661-4EB8-9236-A01737AD98B6`

) made it into the output somehow ... which afaik should not be possible/happen.

I use the interpolation to get all IPs of a resource itself as well since for me it is not an error if you get the list of known IPs at the time of evaluation. (I preset cassandra seeds via ${join(",",instance.cassandra.*.private_ip)})

In the case where only the first instance is created I get a single IP and that list expands while other instances come up.

[mitchellh]

Note you can use the join function which @MerlinDMC mentioned to get the behavior you want.

[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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