Setting Up App Runner Custom Domain with Terraform and Route53

2024/06/15

I work as an engineer in Tokyo!

I mainly work with technologies like TypeScript and Next.js.

Today I'll show you how to configure App Runner DNS targets as A records in Route53 using Terraform!

What We Want to Achieve

App Runner provides a default domain, so you can automatically publish your application on the web once deployment is complete! It's incredibly convenient! However, in most cases, you'll want to use a custom domain instead of the default one. Of course, App Runner also supports custom domain functionality.

https://aws.amazon.com/jp/apprunner/

You can set up a custom domain by configuring the values shown in the image to the target records.

While you can certainly configure these records through the AWS Management Console, I feel that Infrastructure as Code (IaC) usage is increasing, so today I'll configure them using Terraform, which is one of the IaC tools.

Prerequisites

AWS CLI configured
Terraform environment set up
Route53 hosted zone configured

Implementation

First, we'll set up CNAME records for "Certificate Validation" (section 1 in the previous image).

resource "aws_route53_record" "cname_validation_a" {
  name    = var.cert_validation_record_name_a
  zone_id = aws_route53_zone.main_prd.zone_id
  type    = "CNAME"
  ttl     = 300
  records = [var.cert_validation_record_value_a]

  depends_on = [aws_apprunner_service.apprunner]
}
resource "aws_route53_record" "cname_validation_b" {
  name    = var.cert_validation_record_name_b
  zone_id = aws_route53_zone.main_prd.zone_id
  type    = "CNAME"
  ttl     = 300
  records = [var.cert_validation_record_value_b]

  depends_on = [aws_apprunner_service.apprunner]
}
resource "aws_route53_record" "cname_validation_c" {
  name    = var.cert_validation_record_name_c
  zone_id = aws_route53_zone.main_prd.zone_id
  type    = "CNAME"
  ttl     = 300
  records = [var.cert_validation_record_value_c]

  depends_on = [aws_apprunner_service.apprunner]
}

Setting up CNAME records should be straightforward without any particular issues.

The tricky part is "Setting up the DNS target" (section 2 in the image).

I got stuck on this DNS target part. At first, I thought "I should just register this with a CNAME record too," but I got the following error...

 Error: creating Route 53 Record: InvalidChangeBatch: [RRSet of type CNAME with DNS name <domain-name> is not permitted at apex in zone <domain-name>]

This error occurs because, due to CNAME specifications, when an NS record with the same domain name exists, they cannot coexist in the same zone.

https://blog.serverworks.co.jp/dns-cname-record-error

I had set up an NS record with the same name to use an external domain service, which caused this error.

Since DNS targets can also be configured with A records, I'll use that method instead of CNAME. Many articles show examples like this:

//Example
resource "aws_route53_record" "www" {
  zone_id = aws_route53_zone.primary.zone_id
  name    = "example.com"
  type    = "A"

  alias {
    name                   = aws_elb.main.dns_name
    zone_id                = aws_elb.main.zone_id
    evaluate_target_health = true
  }
}

Here you can see there are two zone_ids. The second zone_id represents the ID of the zone where the DNS exists. For App Runner, we need to set the ID of the hosted zone where App Runner's default domain exists. I thought "How would I know that...?" but thankfully, it's publicly available! See the URL below for details.

https://docs.aws.amazon.com/general/latest/gr/apprunner.html

As of 2024/06/15
For ap-northeast-1: Z08491812XW6IPYLR6CCA

Based on this, I configured the A record as follows:

resource "aws_route53_record" "dns_a_record" {
  name    = var.dns_record_name
  zone_id = aws_route53_zone.main_prd.zone_id
  type    = "A"

  alias {
    name = var.dns_record_value
    # NOTE: Reference https://docs.aws.amazon.com/general/latest/gr/apprunner.html
    zone_id                = "Z08491812XW6IPYLR6CCA"
    evaluate_target_health = false
  }

  depends_on = [aws_apprunner_service.apprunner]
}

If you know of a better approach, please let me know!

Thank you for reading to the end!

I tweet casually, so feel free to follow me!

cloudwatch alarm → SNS → AWS Chatbot

イベント通知されない。。😇
Chatbotのテスト送信ができてるのでそこは問題なさそう。Terraformで何か書き忘れているのか。。
— りょた@dev (@Ryo54388667) May 24, 2024

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