fix(source/service): make sure only unique targets available for futher processing

[ivankatliarchuk]

What does it do ?

• Only unique targets pushed to registry for headless services

Motivation

Partially address #4282

follow-up:

• review FQDN behaviour https://github.com/kubernetes-sigs/external-dns/blob/master/docs/tutorials/hostport.md#headless-service, as docs do not looks right to me
• resolve root domain records processing. Find an initial PR, address it or document the behavior

More

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

fixtures used in testing

---
apiVersion: v1
kind: Service
metadata:
  name: kafka
  namespace: default
  labels:
    app: kafka
  annotations:
    external-dns.alpha.kubernetes.io/hostname:  example.org
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: kafka
---
apiVersion: v1
kind: Service
metadata:
  name: kafka-2
  namespace: default
  labels:
    app: kafka
  annotations:
    external-dns.alpha.kubernetes.io/hostname:  example.org
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: kafka
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: kafka
  namespace: default
spec:
  serviceName: "kafka"
  replicas: 3
  selector:
    matchLabels:
      app: kafka
  template:
    metadata:
      labels:
        app: kafka
    spec:
      containers:
      - name: nginx
        image: registry.k8s.io/nginx-slim:0.27
        ports:
        - containerPort: 80
          name: web

smoke test before

{
  "ResourceRecordSets": [
    {
      "Name": "example.org.",
      "Type": "A",
      "TTL": 300,
      "ResourceRecords": [
        {
          "Value": "10.244.1.3"
        },
        {
          "Value": "10.244.1.4"
        },
        {
          "Value": "10.244.1.5"
        }
      ]
    },
    {
      "Name": "example.org.",
      "Type": "NS",
      "TTL": 172800,
      "ResourceRecords": [
        {
          "Value": "ns-2048.awsdns-64.com"
        },
        {
          "Value": "ns-2049.awsdns-65.net"
        },
        {
          "Value": "ns-2050.awsdns-66.org"
        },
        {
          "Value": "ns-2051.awsdns-67.co.uk"
        }
      ]
    },
    {
      "Name": "example.org.",
      "Type": "SOA",
      "TTL": 900,
      "ResourceRecords": [
        {
          "Value": "{'Value': 'ns-2048.awsdns-64.com. hostmaster.example.com. 1 7200 900 1209600 86400'}"
        }
      ]
    },
    {
      "Name": "a-kafka-0.example.org.",
      "Type": "TXT",
      "TTL": 300,
      "ResourceRecords": [
        {
          "Value": "\"heritage=external-dns,external-dns/owner=default,external-dns/resource=service/default/kafka\""
        }
      ]
    },
    {
      "Name": "a-kafka-1.example.org.",
      "Type": "TXT",
      "TTL": 300,
      "ResourceRecords": [
        {
          "Value": "\"heritage=external-dns,external-dns/owner=default,external-dns/resource=service/default/kafka\""
        }
      ]
    },
    {
      "Name": "a-kafka-2.example.org.",
      "Type": "TXT",
      "TTL": 300,
      "ResourceRecords": [
        {
          "Value": "\"heritage=external-dns,external-dns/owner=default,external-dns/resource=service/default/kafka\""
        }
      ]
    },
    {
      "Name": "kafka-0.example.org.",
      "Type": "A",
      "TTL": 300,
      "ResourceRecords": [
        {
          "Value": "10.244.1.3"
        },
        {
          "Value": "10.244.1.3"
        }
      ]
    },
    {
      "Name": "kafka-1.example.org.",
      "Type": "A",
      "TTL": 300,
      "ResourceRecords": [
        {
          "Value": "10.244.1.4"
        },
        {
          "Value": "10.244.1.4"
        }
      ]
    },
    {
      "Name": "kafka-2.example.org.",
      "Type": "A",
      "TTL": 300,
      "ResourceRecords": [
        {
          "Value": "10.244.1.5"
        },
        {
          "Value": "10.244.1.5"
        }
      ]
    }
  ]
}

smoke test after

{
  "ResourceRecordSets": [
    {
      "Name": "example.org.",
      "Type": "A",
      "TTL": 300,
      "ResourceRecords": [
        {
          "Value": "10.244.1.3"
        },
        {
          "Value": "10.244.1.4"
        },
        {
          "Value": "10.244.1.5"
        }
      ]
    },
    {
      "Name": "example.org.",
      "Type": "NS",
      "TTL": 172800,
      "ResourceRecords": [
        {
          "Value": "ns-2048.awsdns-64.com"
        },
        {
          "Value": "ns-2049.awsdns-65.net"
        },
        {
          "Value": "ns-2050.awsdns-66.org"
        },
        {
          "Value": "ns-2051.awsdns-67.co.uk"
        }
      ]
    },
    {
      "Name": "example.org.",
      "Type": "SOA",
      "TTL": 900,
      "ResourceRecords": [
        {
          "Value": "{'Value': 'ns-2048.awsdns-64.com. hostmaster.example.com. 1 7200 900 1209600 86400'}"
        }
      ]
    },
    {
      "Name": "a-kafka-0.example.org.",
      "Type": "TXT",
      "TTL": 300,
      "ResourceRecords": [
        {
          "Value": "\"heritage=external-dns,external-dns/owner=default,external-dns/resource=service/default/kafka\""
        }
      ]
    },
    {
      "Name": "a-kafka-1.example.org.",
      "Type": "TXT",
      "TTL": 300,
      "ResourceRecords": [
        {
          "Value": "\"heritage=external-dns,external-dns/owner=default,external-dns/resource=service/default/kafka\""
        }
      ]
    },
    {
      "Name": "a-kafka-2.example.org.",
      "Type": "TXT",
      "TTL": 300,
      "ResourceRecords": [
        {
          "Value": "\"heritage=external-dns,external-dns/owner=default,external-dns/resource=service/default/kafka\""
        }
      ]
    },
    {
      "Name": "kafka-0.example.org.",
      "Type": "A",
      "TTL": 300,
      "ResourceRecords": [
        {
          "Value": "10.244.1.3"
        }
      ]
    },
    {
      "Name": "kafka-1.example.org.",
      "Type": "A",
      "TTL": 300,
      "ResourceRecords": [
        {
          "Value": "10.244.1.4"
        }
      ]
    },
    {
      "Name": "kafka-2.example.org.",
      "Type": "A",
      "TTL": 300,
      "ResourceRecords": [
        {
          "Value": "10.244.1.5"
        }
      ]
    }
  ]
}

The idea is to address root domain record in follow-up

[mloiseleur]

/lgtm
@szuecs any idea where does come from this somehow unexpected root record creation ?

[ivankatliarchuk]

This is the location of root record

external-dns/source/service.go

Line 360 in 5c42ed0

headlessDomains := []string{hostname}

. I think it should be <service-name>.hostname But not sure

[ivankatliarchuk]

This is a PR #1005 when headless was added, there is no discussions or questioning around root domain records.

[ivankatliarchuk]

Found an issue related #2832

[ivankatliarchuk]

I'm going to merge and open a fix for root domain bug.

[ivankatliarchuk]

/approve

[k8s-ci-robot]

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