dns-delegated

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

If you are deploying a root zone (e.g example.com) rather than a subdomain delegated from a root zone (e.g prod.example.com), and only a single account needs to manage or update the zone you are deploying, then you should use dns-primary instead to deploy that root zone into the target account. See Why not use dns-delegated for all vanity domains? for more details on that.

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

This component should only be deployed globally, which is to say once per account. See Why should the dns-delegated component be deployed globally rather than regionally? for details on why.

Note that once you delegate a subdomain (e.g. prod.example.com) to an account, that account can deploy multiple levels of sub-subdomains (e.g. api.use1.prod.example.com) without further configuration, although you will need to create additional TLS certificates, as the wildcard in a wildcard TLS certificate only matches a single level. You can use our acm component for that.

Usage

Stack Level: Global

Here's an example snippet for how to use this component. Use this component in global 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 refresh 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

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.

Variables

Required Variables

region (string) required

AWS Region

zone_config required

Zone config

Type:

list(object({
subdomain = string
zone_name = string
}))

Optional Variables

aws_shield_protection_enabled (bool) optional

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.

Default value: false

certificate_authority_component_key (string) optional

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

Default value: null

certificate_authority_component_name (string) optional

Use this component name to read from the remote state to get the certificate_authority_arn if using an authority type of SUBORDINATE

Default value: null

certificate_authority_enabled (bool) optional

Whether to use the certificate authority or not

Default value: false

certificate_authority_environment_name (string) optional

Use this environment name to read from the remote state to get the certificate_authority_arn if using an authority type of SUBORDINATE

Default value: null

certificate_authority_stage_name (string) optional

Use this stage name to read from the remote state to get the certificate_authority_arn if using an authority type of SUBORDINATE

Default value: null

dns_private_zone_enabled (bool) optional

Whether to set the zone to public or private

Default value: false

dns_soa_config (string) optional

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 refresh 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.

Default value: "awsdns-hostmaster.amazon.com. 1 7200 900 1209600 60"

request_acm_certificate (bool) optional

Whether or not to create an ACM certificate

Default value: true

vpc_primary_environment_name (string) optional

The name of the environment where primary VPC is deployed

Default value: null

vpc_region_abbreviation_type (string) optional

Type of VPC abbreviation (either fixed or short) to use in names. See https://github.com/cloudposse/terraform-aws-utils for details.

Default value: "fixed"

vpc_secondary_environment_names (list(string)) optional

The names of the environments where secondary VPCs are deployed

Default value: [ ]

Context Variables

The following variables are defined in the context.tf file of this module and part of the terraform-null-label pattern.

additional_tag_map (map(string)) optional

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.

Required: No

Default value: { }

attributes (list(string)) optional

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.

Required: No

Default value: [ ]

context (any) optional

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.

Required: No

Default value:

{
  "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
}

delimiter (string) optional

Delimiter to be used between ID elements.
Defaults to - (hyphen). Set to "" to use no delimiter at all.

Required: No

Default value: null

descriptor_formats (any) optional

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).

Required: No

Default value: { }

enabled (bool) optional

Set to false to prevent the module from creating any resources
Required: No

Default value: null

environment (string) optional

ID element. Usually used for region e.g. 'uw2', 'us-west-2', OR role 'prod', 'staging', 'dev', 'UAT'
Required: No

Default value: null

id_length_limit (number) optional

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.

Required: No

Default value: null

label_key_case (string) optional

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.

Required: No

Default value: null

label_order (list(string)) optional

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.

Required: No

Default value: null

label_value_case (string) optional

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.

Required: No

Default value: null

labels_as_tags (set(string)) optional

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.

Required: No

Default value:

[
  "default"
]

name (string) optional

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.

Required: No

Default value: null

namespace (string) optional

ID element. Usually an abbreviation of your organization name, e.g. 'eg' or 'cp', to help ensure generated IDs are globally unique
Required: No

Default value: null

regex_replace_chars (string) optional

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.

Required: No

Default value: null

stage (string) optional

ID element. Usually used to indicate role, e.g. 'prod', 'staging', 'source', 'build', 'test', 'deploy', 'release'
Required: No

Default value: null

tags (map(string)) optional

Additional tags (e.g. {'BusinessUnit': 'XYZ'}).
Neither the tag keys nor the tag values will be modified by this module.

Required: No

Default value: { }

tenant (string) optional

ID element (Rarely used, not included by default). A customer identifier, indicating who this instance of a resource is for
Required: No

Default value: null

Outputs

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

Dependencies

Requirements

terraform, version: >= 1.0.0
aws, version: >= 4.9.0

Providers

aws, version: >= 4.9.0
aws, version: >= 4.9.0

Modules

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

Resources

The following resources are used by this module:

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)

Data Sources

The following data sources are used by this module:

aws_partition.current (data source)
aws_route53_zone.root_zone (data source)

References

cloudposse/terraform-aws-components - Cloud Posse's upstream component
The dns-primary component.
The acm component component for that.
Why not use dns-delegated for all vanity domains?
Why should the dns-delegated component be deployed globally rather than regionally?

Usage​

Limitations​

Workaround if downtime is fine​

Workaround if downtime is not fine​

Caveats​

Variables​

Required Variables​

Optional Variables​

Context Variables​

Outputs​

Dependencies​

Requirements​

Providers​

Modules​

Resources​

Data Sources​

References​

Usage

Limitations

Workaround if downtime is fine

Workaround if downtime is not fine

Caveats

Variables

Required Variables

Optional Variables

Context Variables

Outputs

Dependencies

Requirements

Providers

Modules

Resources

Data Sources

References