fix(pihole): crash when multiple targets are present with pihole API V6

[codeeno]

Description

Hello,

While trying to set up external-dns (v0.17.0) with Pi-hole (v6.0.6) in my homelab I've come across the following error, placing my pod into CrashLoopBackOff state:

time="2025-05-18T20:57:16Z" level=debug msg="Endpoints generated from ingress: networking/pihole: [pihole.home 0 IN A  10.0.1.10;10.0.1.11 []]"
time="2025-05-18T20:57:16Z" level=info msg="PUT pihole.home IN A -> 10.0.1.10"
time="2025-05-18T20:57:16Z" level=debug msg="Error on request http://pihole-web.networking.svc.cluster.local/api/config/dns/hosts/10.0.1.10%3B10.0.1.11%20pihole.home"

This was with:

env:
  - name: EXTERNAL_DNS_PIHOLE_SERVER
    value: http://pihole-web.networking.svc.cluster.local
  - name: EXTERNAL_DNS_PIHOLE_API_VERSION
    value: "6"

The error happens because all targets are being passed to the generateApiUrl function, even though Pi-hole only supports one target per record and one record per domain. In my case, the targets [10.0.1.10 10.0.1.11] resulted in the API url ending in config/dns/hosts/10.0.1.10%3B10.0.1.11%20pihole.home which the V6 API does not accept.

In the previous implementation, we seemingly have only passed the first of multiple targets. This PR restores that implementation for V6.

Checklist

• Unit tests updated
• End user documentation updated

[linux-foundation-easycla]

• ✅login: codeeno / (0dfbc7e)

The committers listed above are authorized under a signed CLA.

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[k8s-ci-robot]

Hi @codeeno. Thanks for your PR.

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[ivankatliarchuk]

/ok-to-test

[mloiseleur]

@tJouve Do you think you can review this PR ? Wdyt of this approach ?

[Nic0w]

Hi,
Not sure if useful but it looks like I have a related issue :
pihole-external-dns-96bdfcc8b-2m7s4_logs.txt
Looks like external-dns is trying to push both IPv6 addresses of my loadbalancer on only one record.
That sends my pod into a CrashLoopBackoff state.

Pi-hole only supports one target per record and one record per domain.

I think pi-hole does allow multiple records per domains. At least I am able to do configure that by hand in the web interface.

[ivankatliarchuk]

This config multiple/single target should be discoverable

[tJouve]

Hello,

@codeeno Your fix look good and fix a bug.

I will just suggest to change the code to look like ( add Info message and use target := ep.Targets[0] )

        if len(ep.Targets) > 1 {
		log.Infof("Skipping : more than one target, only the first one is keep :  %s %s %s -> %s", action, ep.DNSName, ep.RecordType, ep.targets)
	}
	//
	target := ep.Targets[0]

	if p.cfg.DryRun {
		log.Infof("DRY RUN: %s %s IN %s -> %s", action, ep.DNSName, ep.RecordType, target)
		return nil
	}

	log.Infof("%s %s IN %s -> %s", action, ep.DNSName, ep.RecordType, target)

	// Get the current record
	if strings.Contains(ep.DNSName, "*") {
		return provider.NewSoftError(errors.New("UNSUPPORTED: Pihole DNS names cannot return wildcard"))
	}

	switch ep.RecordType {
	case endpoint.RecordTypeA, endpoint.RecordTypeAAAA:
		apiUrl = p.generateApiUrl(apiUrl, fmt.Sprintf("%s %s", target, ep.DNSName))
	case endpoint.RecordTypeCNAME:
		if ep.RecordTTL.IsConfigured() {
			apiUrl = p.generateApiUrl(apiUrl, fmt.Sprintf("%s,%s,%d", ep.DNSName, target, ep.RecordTTL))
		} else {
			apiUrl = p.generateApiUrl(apiUrl, fmt.Sprintf("%s,%s", ep.DNSName, target))
		}
	}

But in fact it is possible to specify multiples IP for the same A/AAA record .
This statement Pi-hole only supports one target per record and one record per domain is not correct.

This config is legit

And is resolved like that

The definition with the api in one call is not possible, but it will work with 2 different calls


Result in

{
  "config": {
    "dns": {
      "hosts": [
        "192.168.253.253 duplicate.example.net",
        "192.168.253.254 duplicate.example.net"
      ]
    }
  },
  "took": 0.000047206878662109375
}

Deletion also work (one by one):

Maybe we can support this feature by doing something like that :
Iterate over the Targets list then create / delete in separate query to the API.

if len(ep.Targets) == 0 {
		log.Infof("Skipping : missing targets  %s %s %s", action, ep.DNSName, ep.RecordType)
		return nil
	}
	// Get the current record
	if strings.Contains(ep.DNSName, "*") {
		return provider.NewSoftError(errors.New("UNSUPPORTED: Pihole DNS names cannot return wildcard"))
	}

	for _, target := range ep.Targets {
		if p.cfg.DryRun {
			log.Infof("DRY RUN: %s %s IN %s -> %s", action, ep.DNSName, ep.RecordType, target)
			return nil
		}

		log.Infof("%s %s IN %s -> %s", action, ep.DNSName, ep.RecordType, target)

		switch ep.RecordType {
		case endpoint.RecordTypeA, endpoint.RecordTypeAAAA:
			apiUrl = p.generateApiUrl(apiUrl, fmt.Sprintf("%s %s", target, ep.DNSName))
		case endpoint.RecordTypeCNAME:
			if ep.RecordTTL.IsConfigured() {
				apiUrl = p.generateApiUrl(apiUrl, fmt.Sprintf("%s,%s,%d", ep.DNSName, target, ep.RecordTTL))
			} else {
				apiUrl = p.generateApiUrl(apiUrl, fmt.Sprintf("%s,%s", ep.DNSName, target))
			}
		}

		req, err := http.NewRequestWithContext(ctx, action, apiUrl, nil)
		if err != nil {
			return err
		}

		_, err = p.do(req)
		if err != nil {
			return err
		}
	}

What do you think about this implementation ?

[hornet-dev]

I'm running into this too, and I'd prefer to see the implementation that creates A records for each IP address, rather than only create a single record for the first IP address in the list.

[ivankatliarchuk]

Hi @codeeno. Do you think you could address review suggestions?