feat(source): add unstructured source

[ivankatliarchuk]

What does it do ?

A new unstructured source that creates DNS records from any Kubernetes custom resource using Go templates.

Supporting every possible ingress or product isn’t practical. For example, it’s fairly common to have custom products, and ExternalDNS doesn’t really fit that model today, as it doesn’t provide even basic support for custom sources.

Added flags

• --unstructured-resource=
• --target-template=
• --fqd-target-template=

Motivation

We shouldn't have to wait for external-dns to add built-in support for some specific CRDs. With this source, they can point external-dns at any resource (KubeVirt VMs, Crossplane resources, MetalLB pools, etc.) and use templates to extract hostnames and targets from .spec or .status fields.

Fixes #3437
Fixes #5104
Fixes #5922

First attempt #3490. That was abandoned

More

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

I could slice this PR, move tests to another PR and 400+ lines in docs

┌──────────┬───────┐
│ Category │ Lines │
├──────────┼───────┤
│ Non-test │ +462  │
├──────────┼───────┤
│ Test     │ +1613 │
├──────────┼───────┤
│ Docs     │ +435  │
├──────────┼───────┤
│ Ratio    │ 1:3.4 │
└──────────┴───────┘

Follow-up

• add provider specific support

[coveralls]

Pull Request Test Coverage Report for Build 22279424154

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 97 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.05%) to 79.221%

---

Files with Coverage Reduction	New Missed Lines	%
apis/externaldns/types.go	1	99.62%
testutils/endpoint.go	16	71.29%
store.go	80	50.0%

Totals
Change from base Build 22254373828:	-0.05%
Covered Lines:	16249
Relevant Lines:	20511

---

💛 - Coveralls

[vflaux]

That's a nice new feature.
I don't know if other maintainers want to review it too as it's quite big? 🤔

/lgtm

[ivankatliarchuk]

I'll leave it for a week. Sure

[ivankatliarchuk]

Hi @TomyLobo are you still using external-dns? How about to try this feature?

This is related to your comment 2+ years ago #3490 (comment)

[ivankatliarchuk]

This will require golang to be installed https://github.com/kubernetes-sigs/external-dns/blob/master/CONTRIBUTING.md#how-to-test-a-pr

[ivankatliarchuk]

Hi @nazarewk how about to try this feature?

[nazarewk]

Hi @nazarewk how about to try this feature?

Unfortunately I am not working at the original place anymore and won't have access to any external-dns deployment at least for a few weeks.

I had an idea that you could maybe try to use it for the built-in resources, but through the new custom resource interface?

[ivankatliarchuk]

Not a problem. Technically this new source should work with all current and future kubernetes resources.

[Preisschild]

I've tested it with cluster-api machines.v1beta2.cluster.x-k8s.io .status.addresses. Works great. Cool feature

      --unstructured-resource=machines.v1beta2.cluster.x-k8s.io
      --label-filter=cluster.x-k8s.io/control-plane=
      --fqdn-template=< cluster domain >
      --fqdn-target-template={{ range $address := .Status.addresses }}{{ if eq $address.type "ExternalIP"}}{{ $address.address }},{{ end }}{{ end }}

Similar to this discussion: #5922

[ivankatliarchuk]

Nice one. Thank you

[vflaux]

/lgtm

[ivankatliarchuk]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ivankatliarchuk

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Details

Needs approval from an approver in each of these files:

• OWNERS [ivankatliarchuk]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment