Using CRD Source for DNS Records

This tutorial describes how to use the CRD source with ExternalDNS to manage DNS records. The CRD source allows you to define your desired DNS records declaratively using DNSEndpoint custom resources.

Default Targets and CRD Targets

ExternalDNS has a --default-targets flag that can be used to specify a default set of targets for all created DNS records. The behavior of how these default targets interact with targets specified in a DNSEndpoint CRD has been refined.

New Behavior (default)

By default, ExternalDNS now has the following behavior:

• If a DNSEndpoint resource has targets specified in its spec.endpoints[].targets field, these targets will be used for the DNS record, overriding any targets specified via the --default-targets flag.
• If a DNSEndpoint resource has an empty targets field, the targets from the --default-targets flag will be used. This allows for creating records that point to default load balancers or IPs without explicitly listing them in every DNSEndpoint resource.

Legacy Behavior (--force-default-targets)

To maintain backward compatibility and support certain migration scenarios, the --force-default-targets flag is available.

• When --force-default-targets is used, ExternalDNS will always use the targets from --default-targets, regardless of whether the DNSEndpoint resource has targets specified or not. This flag allows for a smooth migration path to the new behavior. It allow keeping old CRD resources, allows to start removing targets from one by one resource and then remove the flag.

Examples

Let's look at how this works in practice. Assume ExternalDNS is running with --default-targets=1.2.3.4.

DNSEndpoint with Targets

Here is a DNSEndpoint with a target specified.

---
apiVersion: externaldns.k8s.io/v1alpha1
kind: DNSEndpoint
metadata:
  name: targets
  namespace: default
spec:
  endpoints:
  - dnsName: smoke-t.example.com
    recordTTL: 300
    recordType: CNAME
    targets:
      - placeholder

• Without --force-default-targets (New Behavior): A CNAME record for smoke-t.example.com will be created pointing to placeholder.
• With --force-default-targets (Legacy Behavior): A CNAME record for smoke-t.example.com will be created pointing to 1.2.3.4. The placeholder target will be ignored.

DNSEndpoint with Empty/No Targets

Here is a DNSEndpoint without any targets specified.

---
apiVersion: externaldns.k8s.io/v1alpha1
kind: DNSEndpoint
metadata:
  name: no-targets
  namespace: default
spec:
  endpoints:
  - dnsName: smoke-nt.example.com
    recordTTL: 300
    recordType: CNAME

• Without --force-default-targets (New Behavior): A CNAME record for smoke-nt.example.com will be created pointing to 1.2.3.4.
• With --force-default-targets (Legacy Behavior): A CNAME record for smoke-nt.example.com will be created pointing to 1.2.3.4.

--force-default-targets allows migration path to clean CRD resources.

DNSEndpoint with an SRV record

Here's an example of a DNSEndpoint with an SRV record:

---
apiVersion: externaldns.k8s.io/v1alpha1
kind: DNSEndpoint
metadata:
  name: test-srv
  namespace: default
spec:
  endpoints:
  - dnsName: _sip._udp.test.example.com
    recordTTL: 180
    recordType: SRV
    targets:
    - 1 50 5060 sip1-n1.test.example.com
    - 1 50 5060 sip1-n2.test.example.com

DNSEndpoint with an NAPTR record

Here's an example of a DNSEndpoint with an NAPTR record:

---
apiVersion: externaldns.k8s.io/v1alpha1
kind: DNSEndpoint
metadata:
  name: test-naptr
  namespace: default
spec:
  endpoints:
  - dnsName: test.example.com
    recordTTL: 180
    recordType: NAPTR
    targets:
    - 50 50 "S" "SIPS+D2T" "" _sips._tcp.test.example.com.
    - 100 50 "S" "SIP+D2U" "" _sip._udp.test.example.com.