# How to Define Multi-string TXT Records

According to DNS-SD, detailed information about a service must be provided in 1 TXT record, as `key=value` pairs.
Different `key=value` pairs must be in separate DNS strings within the same TXT record.

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# In Route53 via Terraform

Terraform expects a list of records. Each record is a Terraform string, and becomes a TXT record. All the DNS strings
for 1 DNS Record must be crammed into 1 Terraform string.

Starting from a Terraform map `var.details`, this can be done like this:

    resource "aws_route53_record" "txt_record" {
      zone_id = "…"
      name    = "…"
      type    = "TXT"
      ttl     = "…"

      records = ["${join("\"\"", formatlist("%s=%s", keys(var.details), values(var.details)))}"]
    }

`formatlist` combines the list of `keys` of the map with the list of `values` of the map into `key=value` pairs using
the pattern `$s=%s`. The result is a list of strings, each of which is a `key=value` pair.

Submitting this like this to `records` results in a separate TXT record per `key=value` pair, which is not what we want.

To transform this list of strings into 1 Terraform string, we need to `join` the list. To make AWS Route53 understand
that the parts are separate DNS strings, each part needs to be enclosed in quotes `"…"`. In several steps, by Terraform
and AWS, quotes `"` are added in front and at the back of this joined string. What is missing are the quotes _between_
the `key=value` pairs. We can add these by using them as a weird join pattern. However, for Terraform to leave them
alone when it passes them to AWS, we need to quote them. The separator pattern thus becomes `\"\"`.

See [@ppwcode/terraform-ppwcode-modules//serviceInstance] for a packaged deal.

## In Route53 via the Web UI

In the Route53 Web UI, we can add several strings on several lines. Each separate line becomes a separate TXT record. It
is thus important to have all our `key=value` pairs on the same line in the TEXTAREA.

To have the AWS Route53 Web UI create separate DNS strings for each `key=value` pair, we need to enclose each
`key=value` pair in double quotes: `"key=value"`, concatenate them (without spaces or other separators) and keep all of
them on one line:

    "apiVersion=v6""at=2017-09-12T16:54:00Z""implVersion=v6""path=/latest""txtvers=1"

## In Dyn.com via the Web UI

None of the above works in the Dyn.com Web UI. It seems like it is impossible to create a multi-string TXT record in
Dyn.com.

A support question was posted, with no answer after a week.

[@ppwcode/terraform-ppwcode-modules//serviceinstance]:
  https://github.com/peopleware/terraform-ppwcode-modules/tree/master/serviceInstance