Terraform: Using join(element(split)) fails

[FransUrbo]

I'm trying to create reverse DNS entry (https://aws.amazon.com/premiumsupport/knowledge-center/route-53-reverse-dns/) but I'm failing..

  name = "${join(".", ["${element(split(".", aws_instance.instance.private_ip), 3)}", "${var.dns-rev}"])}"

This fails with

Error reading config for aws_route53_record[resource]: parse error: syntax error

I know that the element() part works:

  name = "${element(split(".", aws_instance.instance.private_ip), 3)}}"

This will correctly give me the last part of the IP address, but I'm guessing it's the join() that fails (and there especially where I try to give it a list by creating it in place).

[apparentlymart]

Hi @FransUrbo!

As you expected, I think the [ ] syntax for creating a list literal is what's not working here. Terraform doesn't currently allow lists to be constructed like that.

Since you are joining together a known number of items here, you could potentially just use regular string interpolation syntax instead of that join:

name = "${element(split(".", aws_instance.instance.private_ip), 3)}.${var.dns-rev}"

Another option is to use the list() function to produce an inline list. It takes a variable number of string arguments and returns a string list of them all. This is currently the only way to produce a literal list, since we don't have a specific list literal syntax today.

[FransUrbo]

Worked marvelously, thanx!

You don't happen to have an idea on how to do the same for ASG instances as well?

[FransUrbo]

One way to solve this is documented in https://github.com/FransUrbo/Lambda-AWS-AutoScalingGroups-Route53.

However, it's not exactly what I want. It creates a round-robin entry, but I have the ELB for that. What I _would_ like is to have one entry per IP. But I'm starting to think that's impossible due to the restrictions of a Lambda function (must be stateless).

[pselle]

Hi @FransUrbo! It looks like your original question was resolved here, and as we're tidying up issues, I'm going to close this; you might be interested in the community forum for future questions!

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