feat(coredns): add annotations for groups

[farodin91]

What does it do ?

Add support for coredns groups

Motivation

• allow to give test.local a different ip than bla.test.local

More

• Yes, this PR title follows Conventional Commits
• Yes, I added unit tests
• Yes, I updated end user documentation accordingly

[k8s-ci-robot]

Hi @farodin91. Thanks for your PR.

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[ivankatliarchuk]

To review this, you do need to provide more information about what this change is about. As well as use cases, basically as much information as possible, as not clear what we are trying to solve here

[farodin91]

@ivankatliarchuk Idea is to support https://github.com/skynetservices/skydns?tab=readme-ov-file#groups this behavior.

[farodin91]

It is also supported in https://github.com/coredns/coredns/blob/master/plugin/etcd/group_test.go#L40 coredns

[ivankatliarchuk]

Could you share a real-world use case, along with details of your Kubernetes setup for evaluation, so we could try it? Right now, it feels like just code to me and difficult to understand why it should be added.

Documentation missing a tutorial how to as well with use cases example https://github.com/kubernetes-sigs/external-dns/blob/master/docs/advanced/ttl.md#use-cases-for-external-dnsalphakubernetesiottl-annotation-and---min-ttl-flag

We should make sure a new feature doesn’t create more problems before we add it.

[farodin91]

If you create Service A with a DNS address of 'a.k8s.test.local' and an IP address of '10.0.0.1', and then create Service B with a DNS address of 'k8s.test.local' and a different IP address of '10.0.0.2', CoreDNS would currently give 'k8s.test.local' the same IP address as 'a.k8s.test.local' plus the IP of Service B. However, if you use groups, you can prevent this behaviour by assigning different groups to services A and B.

[farodin91]

I will add documentation later. I followed the example of aws for custom annotations.

[farodin91]

@ivankatliarchuk docu added.

[mloiseleur]

/ok-to-test

[ivankatliarchuk]

HI. Could you share a results of your smoke tests. Example #5828 (comment)

[farodin91]

Smoke test

Without Groups

Resources

apiVersion: v1
kind: Service
metadata:
  name: a
  namespace: pt-plat-debug
  annotations:
    external-dns.alpha.kubernetes.io/hostname: a.domain.local
spec:
  type: LoadBalancer
  externalTrafficPolicy: Cluster
  ports:
    - protocol: TCP
      port: 80
---
apiVersion: v1
kind: Service
metadata:
  name: b
  namespace: pt-plat-debug
  annotations:
    external-dns.alpha.kubernetes.io/hostname: b.domain.local
spec:
  type: LoadBalancer
  externalTrafficPolicy: Cluster
  ports:
    - protocol: TCP
      port: 80
---
apiVersion: v1
kind: Service
metadata:
  name: c
  namespace: pt-plat-debug
  annotations:
    external-dns.alpha.kubernetes.io/hostname: c.subdom.domain.local
spec:
  type: LoadBalancer
  externalTrafficPolicy: Cluster
  ports:
    - protocol: TCP
      port: 80
---
apiVersion: v1
kind: Service
metadata:
  name: d
  namespace: pt-plat-debug
  annotations:
    external-dns.alpha.kubernetes.io/hostname: d.subdom.domain.local
spec:
  type: LoadBalancer
  externalTrafficPolicy: Cluster
  ports:
    - protocol: TCP
      port: 80

nslookup

$ nslookup domain.local
Server:         10.0.0.1
Address:        10.0.0.1#53

Non-authoritative answer:
Name:   domain.local
Address: 10.0.1.4
Name:   domain.local
Address: 10.0.1.2
Name:   domain.local
Address: 10.0.1.5
Name:   domain.local
Address: 10.0.1.3

$ nslookup subdom.domain.local
Server:         10.0.0.1
Address:        10.0.0.1#53

Non-authoritative answer:
Name:   subdom.domain.local
Address: 10.0.1.5
Name:   subdom.domain.local
Address: 10.0.1.4

With Groups

Resources

apiVersion: v1
kind: Service
metadata:
  name: a
  namespace: pt-plat-debug
  annotations:
    external-dns.alpha.kubernetes.io/hostname: a.domain.local
    external-dns.alpha.kubernetes.io/coredns-group: "g1"
spec:
  type: LoadBalancer
  externalTrafficPolicy: Cluster
  ports:
    - protocol: TCP
      port: 80
---
apiVersion: v1
kind: Service
metadata:
  name: b
  namespace: pt-plat-debug
  annotations:
    external-dns.alpha.kubernetes.io/hostname: b.domain.local
    external-dns.alpha.kubernetes.io/coredns-group: "g1"
spec:
  type: LoadBalancer
  externalTrafficPolicy: Cluster
  ports:
    - protocol: TCP
      port: 80
---
apiVersion: v1
kind: Service
metadata:
  name: c
  namespace: pt-plat-debug
  annotations:
    external-dns.alpha.kubernetes.io/hostname: c.subdom.domain.local
    external-dns.alpha.kubernetes.io/coredns-group: "g2"
spec:
  type: LoadBalancer
  externalTrafficPolicy: Cluster
  ports:
    - protocol: TCP
      port: 80
---
apiVersion: v1
kind: Service
metadata:
  name: d
  namespace: pt-plat-debug
  annotations:
    external-dns.alpha.kubernetes.io/hostname: d.subdom.domain.local
    external-dns.alpha.kubernetes.io/coredns-group: "g2"
spec:
  type: LoadBalancer
  externalTrafficPolicy: Cluster
  ports:
    - protocol: TCP
      port: 80

nslookup

$ nslookup domain.local
Server:         10.0.0.1
Address:        10.0.0.1#53

Non-authoritative answer:
Name:   domain.local
Address: 10.0.1.2
Name:   domain.local
Address: 10.0.1.3

$ nslookup subdom.domain.local
Server:         10.0.0.1
Address:        10.0.0.1#53

Non-authoritative answer:
Name:   subdom.domain.local
Address: 10.0.1.5
Name:   subdom.domain.local
Address: 10.0.1.4

[ivankatliarchuk]

Missing code coverage. Rest seems ok

[farodin91]

@ivankatliarchuk rebased and test added.

[ivankatliarchuk]

/lgtm

[k8s-ci-robot]

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