Terraformのaws_route53_recordで作成したリソースの変数を取得しようとしたら、エラーが出たので解決法を載せます。
使用しているTerraform/probider awsのバージョンはTerraform v0.12.5 + provider.aws v3.4.0です。

エラー内容

Error: Invalid index

  on main.tf line 124, in resource "aws_route53_record" "example_certificate":
 124:   name      = aws_acm_certificate.example.domain_validation_options[0].resource_rcord_name

This value does not have any indices.


Error: Invalid index

  on main.tf line 125, in resource "aws_route53_record" "example_certificate":
 125:   type      = aws_acm_certificate.example.domain_validation_options[0].resource_record_type

This value does not have any indices.


Error: Invalid index

  on main.tf line 126, in resource "aws_route53_record" "example_certificate":
 126:   records   = [aws_acm_certificate.example.domain_validation_options[0].resource_record_value]

This value does not have any indices.

使用したコード

main.tf


resource "aws_acm_certificate" "example" {
  domain_name               = "xxxxxxx.com"
  subject_alternative_names = ["*.xxxxxxx.com"]
  validation_method         = "DNS"

  lifecycle {
    create_before_destroy = true
  }
}

resource "aws_route53_record" "example_certificate" {
  name      = aws_acm_certificate.example.domain_validation_options[0].resource_rcord_name
  type      = aws_acm_certificate.example.domain_validation_options[0].resource_record_type
  records   = [aws_acm_certificate.example.domain_validation_options[0].resource_record_value]
  zone_id   = data.aws_route53_zone.example.zone_id
  ttl       = 60
}

解決方法

mapのリストにうまくアクセス出来ていないかったようです。
表記方法変えたらエラーなくなりました。

main.tf

name      = aws_acm_certificate.example.domain_validation_options[0].resource_rcord_name
↓
name      = aws_acm_certificate.example.domain_validation_options.*.resource_record_name[0]

ちなみにterraform consoleを使えば対話的にリソースの確認も出来るのでデバッグに便利でした。

$ terraform console
> aws_acm_certificate.example.domain_validation_options
[
  {
    "domain_name" = "*.xxxxxxx.com"
    "resource_record_name" = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.xxxxxxx.com."
    "resource_record_type" = "CNAME"
    "resource_record_value" = "xxxxxxxxxxxxxxxxxxxxxxxxx.xxxxxxxx.acm-validations.aws."
  },
  {
    "domain_name" = "xxxxxxx.com"
    "resource_record_name" = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.xxxxxxx.com."
    "resource_record_type" = "CNAME"
    "resource_record_value" = "xxxxxxxxxxxxxxxxxxxxxxxxx.xxxxxxxx.acm-validations.aws."
  },
]
>