Component: `dns-delegated`

This component is responsible for provisioning a DNS zone which delegates nameservers to the DNS zone in the primary DNS account. The primary DNS zone is expected to already be provisioned via the dns-primary component.

This component also provisions a wildcard ACM certificate for the given subdomain.

Usage

Stack Level: Global or Regional

Here's an example snippet for how to use this component. Use this component in global or regional stacks for any accounts where you host services that need DNS records on a given subdomain (e.g. delegated zone) of the root domain (e.g. primary zone).

Public Hosted Zone devplatform.example.net will be created and example.net HZ in the dns primary account will contain a record delegating DNS to the new HZ

This will create an ACM record

components:
  terraform:
    dns-delegated:
      vars:
        zone_config:
          - subdomain: devplatform
            zone_name: example.net
        request_acm_certificate: true
        dns_private_zone_enabled: false
        #  dns_soa_config configures the SOA record for the zone::
        #    - awsdns-hostmaster.amazon.com. ; AWS default value for administrator email address
        #    - 1 ; serial number, not used by AWS
        #    - 7200 ; refresh time in seconds for secondary DNS servers to refreh SOA record
        #    - 900 ; retry time in seconds for secondary DNS servers to retry failed SOA record update
        #    - 1209600 ; expire time in seconds (1209600 is 2 weeks) for secondary DNS servers to remove SOA record if they cannot refresh it
        #    - 60 ; nxdomain TTL, or time in seconds for secondary DNS servers to cache negative responses
        #    See [SOA Record Documentation](https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/SOA-NSrecords.html) for more information.
        dns_soa_config: "awsdns-hostmaster.amazon.com. 1 7200 900 1209600 60"

Private Hosted Zone devplatform.example.net will be created and example.net HZ in the dns primary account will contain a record delegating DNS to the new HZ

This will create an ACM record using a Private CA

components:
  terraform:
    dns-delegated:
      vars:
        zone_config:
          - subdomain: devplatform
            zone_name: example.net
        request_acm_certificate: true
        dns_private_zone_enabled: true
        vpc_region_abbreviation_type: short
        vpc_primary_environment_name: use2
        certificate_authority_component_name: private-ca-subordinate
        certificate_authority_stage_name: pca
        certificate_authority_environment_name: use2
        certificate_authority_component_key: subordinate

Limitations

Switching a hosted zone from public to private can cause issues because the provider will try to do an update instead of a ForceNew.

See: https://github.com/hashicorp/terraform-provider-aws/issues/7614

It's not possible to toggle between public and private so if switching from public to private and downtime is acceptable, delete the records of the hosted zone, delete the hosted zone, destroy the terraform component, and deploy with the new settings.

NOTE: With each of these workarounds, you may have an issue connecting to the service specific provider e.g. for auroro-postgres you may get an error of the host set to localhost on the postgresql provider resulting in an error. To get around this, dump the endpoint using atmos terraform show, hardcode the host input on the provider, and re-run the apply.

Workaround if downtime is fine

Delete anything using ACMs connected to previous hosted zones
Delete ACMs
Delete entries in public hosted zone
Delete hosted zone
Use atmos to destroy dns-delegated to remove the public hosted zone
Use atmos to deploy dns-delegated for the private hosted zone
Move aurora-postgres, msk, external-dns, echo-server, etc to the new hosted zone by re-deploying

Workaround if downtime is not fine

Create a new virtual component of dns-delegated with the correct private inputs (see above)
Deploy the new dns-delegated-private component
Move aurora-postgres, msk, external-dns, echo-server, etc to the new hosted zone by re-deploying

Caveats

Do not create a delegation for subdomain of a domain in a zone for which that zone is not authoritative for the subdomain (usually because you already delegated a parent subdomain). Though Amazon Route 53 will allow you to, you should not do it. For historic reasons, Route 53 Public DNS allows customers to create two NS delegations within a hosted zone which creates a conflict (and can return either set to resolvers depending on the query).

For example, in a single hosted zone with the domain name example.com, it is possible to create two NS delegations which are parent and child of each other as follows:

a.example.com. 172800 IN NS ns-1084.awsdns-07.org.
a.example.com. 172800 IN NS ns-634.awsdns-15.net.
a.example.com. 172800 IN NS ns-1831.awsdns-36.co.uk.
a.example.com. 172800 IN NS ns-190.awsdns-23.com.

b.a.example.com. 172800 IN NS ns-1178.awsdns-19.org.
b.a.example.com. 172800 IN NS ns-614.awsdns-12.net.
b.a.example.com. 172800 IN NS ns-1575.awsdns-04.co.uk.
b.a.example.com. 172800 IN NS ns-338.awsdns-42.com.

This configuration creates two discrete possible resolution paths.

If a resolver directly queries the example.com nameservers for c.b.a.example.com, it will receive the second set of nameservers.
If a resolver queries example.com for a.example.com, it will receive the first set of nameservers.

If the resolver then proceeds to query the a.example.com nameservers for c.b.a.example.com, the response is driven by the contents of the a.example.com zone, which may be different than the results returned by the b.a.example.com nameservers. c.b.a.example.com may not have an entry in the a.example.com nameservers, resulting in an error (NXDOMAIN) being returned.

From 15th May 2020, Route 53 Resolver has been enabling a modern DNS resolver standard called "QName Minimization"[*]. This change causes the resolver to more strictly use recursion path [2] described above where path [1] was common before. [*][https://tools.ietf.org/html/rfc7816](https://tools.ietf.org/html/rfc7816)

As of January 2022, you can observe the different query strategies in use by Google DNS at 8.8.8.8 (strategy 1) and Cloudflare DNS at 1.1.1.1 (strategy 2). You should verify that both DNS servers resolve your host records properly.

Takeaway

In order to ensure DNS resolution is consistent no matter the resolver, it is important to always create NS delegations only authoritative zones.

Requirements

Name	Version
terraform	>= 1.0.0
aws	>= 4.9.0

Providers

Name	Version
aws	>= 4.9.0
aws.primary	>= 4.9.0

Modules

Name	Source	Version
acm	cloudposse/acm-request-certificate/aws	0.17.0
iam_roles	../account-map/modules/iam-roles	n/a
private_ca	cloudposse/stack-config/yaml//modules/remote-state	1.5.0
this	cloudposse/label/null	0.25.0
utils	cloudposse/utils/aws	1.3.0
vpc	cloudposse/stack-config/yaml//modules/remote-state	1.5.0

Resources

Name	Type
aws_route53_record.root_ns	resource
aws_route53_record.soa	resource
aws_route53_zone.default	resource
aws_route53_zone.private	resource
aws_route53_zone_association.secondary	resource
aws_shield_protection.shield_protection	resource
aws_ssm_parameter.acm_arn	resource
aws_partition.current	data source
aws_route53_zone.root_zone	data source

Inputs

Name	Description	Type	Default	Required
additional_tag_map	Additional key-value pairs to add to each map in `tags_as_list_of_maps`. Not added to `tags` or `id`. This is for some rare cases where resources want additional configuration of tags and therefore take a list of maps with tag key, value, and additional configuration.	`map(string)`	`{}`	no
attributes	ID element. Additional attributes (e.g. `workers` or `cluster`) to add to `id`, in the order they appear in the list. New attributes are appended to the end of the list. The elements of the list are joined by the `delimiter` and treated as a single ID element.	`list(string)`	`[]`	no
aws_shield_protection_enabled	Enable or disable AWS Shield Advanced protection for Route53 Zones. If set to 'true', a subscription to AWS Shield Advanced must exist in this account.	`bool`	`false`	no
certificate_authority_component_key	Use this component key e.g. `root` or `mgmt` to read from the remote state to get the certificate_authority_arn if using an authority type of SUBORDINATE	`string`	`null`	no
certificate_authority_component_name	Use this component name to read from the remote state to get the certificate_authority_arn if using an authority type of SUBORDINATE	`string`	`null`	no
certificate_authority_enabled	Whether to use the certificate authority or not	`bool`	`false`	no
certificate_authority_environment_name	Use this environment name to read from the remote state to get the certificate_authority_arn if using an authority type of SUBORDINATE	`string`	`null`	no
certificate_authority_stage_name	Use this stage name to read from the remote state to get the certificate_authority_arn if using an authority type of SUBORDINATE	`string`	`null`	no
context	Single object for setting entire context at once. See description of individual variables for details. Leave string and numeric variables as `null` to use default value. Individual variable settings (non-null) override settings in context object, except for attributes, tags, and additional_tag_map, which are merged.	`any`	`{ "additional_tag_map": {}, "attributes": [], "delimiter": null, "descriptor_formats": {}, "enabled": true, "environment": null, "id_length_limit": null, "label_key_case": null, "label_order": [], "label_value_case": null, "labels_as_tags": [ "unset" ], "name": null, "namespace": null, "regex_replace_chars": null, "stage": null, "tags": {}, "tenant": null }`	no
delimiter	Delimiter to be used between ID elements. Defaults to `-` (hyphen). Set to `""` to use no delimiter at all.	`string`	`null`	no
descriptor_formats	Describe additional descriptors to be output in the `descriptors` output map. Map of maps. Keys are names of descriptors. Values are maps of the form `{<br/> format = string<br/> labels = list(string)<br/>}` (Type is `any` so the map values can later be enhanced to provide additional options.) `format` is a Terraform format string to be passed to the `format()` function. `labels` is a list of labels, in order, to pass to `format()` function. Label values will be normalized before being passed to `format()` so they will be identical to how they appear in `id`. Default is `{}` (`descriptors` output will be empty).	`any`	`{}`	no
dns_private_zone_enabled	Whether to set the zone to public or private	`bool`	`false`	no
dns_soa_config	Root domain name DNS SOA record: - awsdns-hostmaster.amazon.com. ; AWS default value for administrator email address - 1 ; serial number, not used by AWS - 7200 ; refresh time in seconds for secondary DNS servers to refreh SOA record - 900 ; retry time in seconds for secondary DNS servers to retry failed SOA record update - 1209600 ; expire time in seconds (1209600 is 2 weeks) for secondary DNS servers to remove SOA record if they cannot refresh it - 60 ; nxdomain TTL, or time in seconds for secondary DNS servers to cache negative responses See SOA Record Documentation for more information.	`string`	`"awsdns-hostmaster.amazon.com. 1 7200 900 1209600 60"`	no
enabled	Set to false to prevent the module from creating any resources	`bool`	`null`	no
environment	ID element. Usually used for region e.g. 'uw2', 'us-west-2', OR role 'prod', 'staging', 'dev', 'UAT'	`string`	`null`	no
id_length_limit	Limit `id` to this many characters (minimum 6). Set to `0` for unlimited length. Set to `null` for keep the existing setting, which defaults to `0`. Does not affect `id_full`.	`number`	`null`	no
label_key_case	Controls the letter case of the `tags` keys (label names) for tags generated by this module. Does not affect keys of tags passed in via the `tags` input. Possible values: `lower`, `title`, `upper`. Default value: `title`.	`string`	`null`	no
label_order	The order in which the labels (ID elements) appear in the `id`. Defaults to ["namespace", "environment", "stage", "name", "attributes"]. You can omit any of the 6 labels ("tenant" is the 6th), but at least one must be present.	`list(string)`	`null`	no
label_value_case	Controls the letter case of ID elements (labels) as included in `id`, set as tag values, and output by this module individually. Does not affect values of tags passed in via the `tags` input. Possible values: `lower`, `title`, `upper` and `none` (no transformation). Set this to `title` and set `delimiter` to `""` to yield Pascal Case IDs. Default value: `lower`.	`string`	`null`	no
labels_as_tags	Set of labels (ID elements) to include as tags in the `tags` output. Default is to include all labels. Tags with empty values will not be included in the `tags` output. Set to `[]` to suppress all generated tags. Notes: The value of the `name` tag, if included, will be the `id`, not the `name`. Unlike other `null-label` inputs, the initial setting of `labels_as_tags` cannot be changed in later chained modules. Attempts to change it will be silently ignored.	`set(string)`	`[ "default" ]`	no
name	ID element. Usually the component or solution name, e.g. 'app' or 'jenkins'. This is the only ID element not also included as a `tag`. The "name" tag is set to the full `id` string. There is no tag with the value of the `name` input.	`string`	`null`	no
namespace	ID element. Usually an abbreviation of your organization name, e.g. 'eg' or 'cp', to help ensure generated IDs are globally unique	`string`	`null`	no
regex_replace_chars	Terraform regular expression (regex) string. Characters matching the regex will be removed from the ID elements. If not set, `"/[^a-zA-Z0-9-]/"` is used to remove all characters other than hyphens, letters and digits.	`string`	`null`	no
region	AWS Region	`string`	n/a	yes
request_acm_certificate	Whether or not to create an ACM certificate	`bool`	`true`	no
stage	ID element. Usually used to indicate role, e.g. 'prod', 'staging', 'source', 'build', 'test', 'deploy', 'release'	`string`	`null`	no
tags	Additional tags (e.g. `{'BusinessUnit': 'XYZ'}`). Neither the tag keys nor the tag values will be modified by this module.	`map(string)`	`{}`	no
tenant	ID element _(Rarely used, not included by default)_. A customer identifier, indicating who this instance of a resource is for	`string`	`null`	no
vpc_primary_environment_name	The name of the environment where primary VPC is deployed	`string`	`null`	no
vpc_region_abbreviation_type	Type of VPC abbreviation (either `fixed` or `short`) to use in names. See https://github.com/cloudposse/terraform-aws-utils for details.	`string`	`"fixed"`	no
vpc_secondary_environment_names	The names of the environments where secondary VPCs are deployed	`list(string)`	`[]`	no
zone_config	Zone config	`list(object({ subdomain = string zone_name = string }))`	n/a	yes

Outputs

Name	Description
acm_ssm_parameter	The SSM parameter for the ACM cert.
certificate	The ACM certificate information.
default_dns_zone_id	Default root DNS zone ID for the cluster
default_domain_name	Default root domain name (e.g. dev.example.net) for the cluster
route53_hosted_zone_protections	List of AWS Shield Advanced Protections for Route53 Hosted Zones.
zones	Subdomain and zone config

References

cloudposse/terraform-aws-components - Cloud Posse's upstream component

Component: dns-delegated

Usage​

Limitations​

Workaround if downtime is fine​

Workaround if downtime is not fine​

Caveats​

Requirements​

Providers​

Modules​

Resources​

Inputs​

Outputs​

References​